stl_algo.h source code [include/c++/15.2.1/bits/stl_algo.h]

1	// Algorithm implementation -- C++ --
2
3	// Copyright (C) 2001-2025 Free Software Foundation, Inc.
4	//
5	// This file is part of the GNU ISO C++ Library. This library is free
6	// software; you can redistribute it and/or modify it under the
7	// terms of the GNU General Public License as published by the
8	// Free Software Foundation; either version 3, or (at your option)
9	// any later version.
10
11	// This library is distributed in the hope that it will be useful,
12	// but WITHOUT ANY WARRANTY; without even the implied warranty of
13	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14	// GNU General Public License for more details.
15
16	// Under Section 7 of GPL version 3, you are granted additional
17	// permissions described in the GCC Runtime Library Exception, version
18	// 3.1, as published by the Free Software Foundation.
19
20	// You should have received a copy of the GNU General Public License and
21	// a copy of the GCC Runtime Library Exception along with this program;
22	// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23	// <http://www.gnu.org/licenses/>.
24
25	/*
26	*
27	* Copyright (c) 1994
28	* Hewlett-Packard Company
29	*
30	* Permission to use, copy, modify, distribute and sell this software
31	* and its documentation for any purpose is hereby granted without fee,
32	* provided that the above copyright notice appear in all copies and
33	* that both that copyright notice and this permission notice appear
34	* in supporting documentation. Hewlett-Packard Company makes no
35	* representations about the suitability of this software for any
36	* purpose. It is provided "as is" without express or implied warranty.
37	*
38	*
39	* Copyright (c) 1996
40	* Silicon Graphics Computer Systems, Inc.
41	*
42	* Permission to use, copy, modify, distribute and sell this software
43	* and its documentation for any purpose is hereby granted without fee,
44	* provided that the above copyright notice appear in all copies and
45	* that both that copyright notice and this permission notice appear
46	* in supporting documentation. Silicon Graphics makes no
47	* representations about the suitability of this software for any
48	* purpose. It is provided "as is" without express or implied warranty.
49	*/
50
51	/* @file bits/stl_algo.h*
52	* This is an internal header file, included by other library headers.
53	* Do not attempt to use it directly. @headername{algorithm}
54	*/
55
56	#ifndef _STL_ALGO_H
57	#define _STL_ALGO_H 1
58
59	#include <bits/algorithmfwd.h>
60	#include <bits/stl_algobase.h>
61	#include <bits/stl_heap.h>
62	#include <bits/predefined_ops.h>
63
64	#if __cplusplus >= 201103L
65	#include <bits/uniform_int_dist.h>
66	#endif
67
68	#if _GLIBCXX_HOSTED
69	# include <bits/stl_tempbuf.h> // for _Temporary_buffer
70	# if (__cplusplus <= 201103L \|\| _GLIBCXX_USE_DEPRECATED)
71	# include <cstdlib> // for rand
72	# endif
73	#endif
74
75	#pragma GCC diagnostic push
76	#pragma GCC diagnostic ignored "-Wc++11-extensions" // inline namespace
77
78	// See concept_check.h for the __glibcxx__requires macros.*
79
80	namespace std _GLIBCXX_VISIBILITY(default)
81	{
82	_GLIBCXX_BEGIN_NAMESPACE_VERSION
83
84	/// Swaps the median value of __a, __b and __c under __comp to __result
85	template<typename _Iterator, typename _Compare>
86	_GLIBCXX20_CONSTEXPR
87	void
88	__move_median_to_first(_Iterator __result,_Iterator __a, _Iterator __b,
89	_Iterator __c, _Compare __comp)
90	{
91	if (__comp(__a, __b))
92	{
93	if (__comp(__b, __c))
94	std::iter_swap(__result, __b);
95	else if (__comp(__a, __c))
96	std::iter_swap(__result, __c);
97	else
98	std::iter_swap(__result, __a);
99	}
100	else if (__comp(__a, __c))
101	std::iter_swap(__result, __a);
102	else if (__comp(__b, __c))
103	std::iter_swap(__result, __c);
104	else
105	std::iter_swap(__result, __b);
106	}
107
108	/// Provided for stable_partition to use.
109	template<typename _InputIterator, typename _Predicate>
110	_GLIBCXX20_CONSTEXPR
111	inline _InputIterator
112	__find_if_not(_InputIterator __first, _InputIterator __last,
113	_Predicate __pred)
114	{
115	return std::__find_if(__first, __last,
116	__gnu_cxx::__ops::__negate(__pred));
117	}
118
119	/// Like find_if_not(), but uses and updates a count of the
120	/// remaining range length instead of comparing against an end
121	/// iterator.
122	template<typename _InputIterator, typename _Predicate, typename _Distance>
123	_GLIBCXX20_CONSTEXPR
124	_InputIterator
125	__find_if_not_n(_InputIterator __first, _Distance& __len, _Predicate __pred)
126	{
127	for (; __len; --__len, (void) ++__first)
128	if (!__pred(__first))
129	break;
130	return __first;
131	}
132
133	// set_difference
134	// set_intersection
135	// set_symmetric_difference
136	// set_union
137	// for_each
138	// find
139	// find_if
140	// find_first_of
141	// adjacent_find
142	// count
143	// count_if
144	// search
145	// search_n
146
147	/**
148	* This is an helper function for search_n overloaded for forward iterators.
149	*/
150	template<typename _ForwardIterator, typename _Integer,
151	typename _UnaryPredicate>
152	_GLIBCXX20_CONSTEXPR
153	_ForwardIterator
154	__search_n_aux(_ForwardIterator __first, _ForwardIterator __last,
155	_Integer __count, _UnaryPredicate __unary_pred,
156	std::forward_iterator_tag)
157	{
158	__first = std::__find_if(__first, __last, __unary_pred);
159	while (__first != __last)
160	{
161	typename iterator_traits<_ForwardIterator>::difference_type
162	__n = __count;
163	_ForwardIterator __i = __first;
164	++__i;
165	while (__i != __last && __n != `1` && __unary_pred(__i))
166	{
167	++__i;
168	--__n;
169	}
170	if (__n == `1`)
171	return __first;
172	if (__i == __last)
173	return __last;
174	__first = std::__find_if(++__i, __last, __unary_pred);
175	}
176	return __last;
177	}
178
179	/**
180	* This is an helper function for search_n overloaded for random access
181	* iterators.
182	*/
183	template<typename _RandomAccessIter, typename _Integer,
184	typename _UnaryPredicate>
185	_GLIBCXX20_CONSTEXPR
186	_RandomAccessIter
187	__search_n_aux(_RandomAccessIter __first, _RandomAccessIter __last,
188	_Integer __count, _UnaryPredicate __unary_pred,
189	std::random_access_iterator_tag)
190	{
191	typedef typename std::iterator_traits<_RandomAccessIter>::difference_type
192	_DistanceType;
193
194	_DistanceType __tailSize = __last - __first;
195	_DistanceType __remainder = __count;
196
197	while (__remainder <= __tailSize) // the main loop...
198	{
199	__first += __remainder;
200	__tailSize -= __remainder;
201	// __first here is always pointing to one past the last element of
202	// next possible match.
203	_RandomAccessIter __backTrack = __first;
204	while (__unary_pred(--__backTrack))
205	{
206	if (--__remainder == `0`)
207	return (__first - __count); // Success
208	}
209	__remainder = __count + `1` - (__first - __backTrack);
210	}
211	return __last; // Failure
212	}
213
214	template<typename _ForwardIterator, typename _Integer,
215	typename _UnaryPredicate>
216	_GLIBCXX20_CONSTEXPR
217	_ForwardIterator
218	__search_n(_ForwardIterator __first, _ForwardIterator __last,
219	_Integer __count,
220	_UnaryPredicate __unary_pred)
221	{
222	if (__count <= `0`)
223	return __first;
224
225	if (__count == `1`)
226	return std::__find_if(__first, __last, __unary_pred);
227
228	return std::__search_n_aux(__first, __last, __count, __unary_pred,
229	std::__iterator_category(__first));
230	}
231
232	// find_end for forward iterators.
233	template<typename _ForwardIterator1, typename _ForwardIterator2,
234	typename _BinaryPredicate>
235	_GLIBCXX20_CONSTEXPR
236	_ForwardIterator1
237	__find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
238	_ForwardIterator2 __first2, _ForwardIterator2 __last2,
239	forward_iterator_tag, forward_iterator_tag,
240	_BinaryPredicate __comp)
241	{
242	if (__first2 == __last2)
243	return __last1;
244
245	_ForwardIterator1 __result = __last1;
246	while (`1`)
247	{
248	_ForwardIterator1 __new_result
249	= std::__search(__first1, __last1, __first2, __last2, __comp);
250	if (__new_result == __last1)
251	return __result;
252	else
253	{
254	__result = __new_result;
255	__first1 = __new_result;
256	++__first1;
257	}
258	}
259	}
260
261	// find_end for bidirectional iterators (much faster).
262	template<typename _BidirectionalIterator1, typename _BidirectionalIterator2,
263	typename _BinaryPredicate>
264	_GLIBCXX20_CONSTEXPR
265	_BidirectionalIterator1
266	__find_end(_BidirectionalIterator1 __first1,
267	_BidirectionalIterator1 __last1,
268	_BidirectionalIterator2 __first2,
269	_BidirectionalIterator2 __last2,
270	bidirectional_iterator_tag, bidirectional_iterator_tag,
271	_BinaryPredicate __comp)
272	{
273	// concept requirements
274	__glibcxx_function_requires(_BidirectionalIteratorConcept<
275	_BidirectionalIterator1>)
276	__glibcxx_function_requires(_BidirectionalIteratorConcept<
277	_BidirectionalIterator2>)
278
279	typedef reverse_iterator<_BidirectionalIterator1> _RevIterator1;
280	typedef reverse_iterator<_BidirectionalIterator2> _RevIterator2;
281
282	_RevIterator1 __rlast1(__first1);
283	_RevIterator2 __rlast2(__first2);
284	_RevIterator1 __rresult = std::__search(_RevIterator1(__last1), __rlast1,
285	_RevIterator2(__last2), __rlast2,
286	__comp);
287
288	if (__rresult == __rlast1)
289	return __last1;
290	else
291	{
292	_BidirectionalIterator1 __result = __rresult.base();
293	std::advance(__result, -std::distance(__first2, __last2));
294	return __result;
295	}
296	}
297
298	/**
299	* @brief Find last matching subsequence in a sequence.
300	* @ingroup non_mutating_algorithms
301	* @param __first1 Start of range to search.
302	* @param __last1 End of range to search.
303	* @param __first2 Start of sequence to match.
304	* @param __last2 End of sequence to match.
305	* @return The last iterator @c i in the range
306	* @p [__first1,__last1-(__last2-__first2)) such that @c *(i+N) ==
307	* @p *(__first2+N) for each @c N in the range @p
308	* [0,__last2-__first2), or @p __last1 if no such iterator exists.
309	*
310	* Searches the range @p [__first1,__last1) for a sub-sequence that
311	* compares equal value-by-value with the sequence given by @p
312	* [__first2,__last2) and returns an iterator to the __first
313	* element of the sub-sequence, or @p __last1 if the sub-sequence
314	* is not found. The sub-sequence will be the last such
315	* subsequence contained in [__first1,__last1).
316	*
317	* Because the sub-sequence must lie completely within the range @p
318	* [__first1,__last1) it must start at a position less than @p
319	* __last1-(__last2-__first2) where @p __last2-__first2 is the
320	* length of the sub-sequence. This means that the returned
321	* iterator @c i will be in the range @p
322	* [__first1,__last1-(__last2-__first2))
323	*/
324	template<typename _ForwardIterator1, typename _ForwardIterator2>
325	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
326	inline _ForwardIterator1
327	find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
328	_ForwardIterator2 __first2, _ForwardIterator2 __last2)
329	{
330	// concept requirements
331	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
332	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
333	__glibcxx_function_requires(_EqualOpConcept<
334	typename iterator_traits<_ForwardIterator1>::value_type,
335	typename iterator_traits<_ForwardIterator2>::value_type>)
336	__glibcxx_requires_valid_range(__first1, __last1);
337	__glibcxx_requires_valid_range(__first2, __last2);
338
339	return std::__find_end(__first1, __last1, __first2, __last2,
340	std::__iterator_category(__first1),
341	std::__iterator_category(__first2),
342	__gnu_cxx::__ops::__iter_equal_to_iter());
343	}
344
345	/**
346	* @brief Find last matching subsequence in a sequence using a predicate.
347	* @ingroup non_mutating_algorithms
348	* @param __first1 Start of range to search.
349	* @param __last1 End of range to search.
350	* @param __first2 Start of sequence to match.
351	* @param __last2 End of sequence to match.
352	* @param __comp The predicate to use.
353	* @return The last iterator @c i in the range @p
354	* [__first1,__last1-(__last2-__first2)) such that @c
355	* predicate(*(i+N), @p (__first2+N)) is true for each @c N in the
356	* range @p [0,__last2-__first2), or @p __last1 if no such iterator
357	* exists.
358	*
359	* Searches the range @p [__first1,__last1) for a sub-sequence that
360	* compares equal value-by-value with the sequence given by @p
361	* [__first2,__last2) using comp as a predicate and returns an
362	* iterator to the first element of the sub-sequence, or @p __last1
363	* if the sub-sequence is not found. The sub-sequence will be the
364	* last such subsequence contained in [__first,__last1).
365	*
366	* Because the sub-sequence must lie completely within the range @p
367	* [__first1,__last1) it must start at a position less than @p
368	* __last1-(__last2-__first2) where @p __last2-__first2 is the
369	* length of the sub-sequence. This means that the returned
370	* iterator @c i will be in the range @p
371	* [__first1,__last1-(__last2-__first2))
372	*/
373	template<typename _ForwardIterator1, typename _ForwardIterator2,
374	typename _BinaryPredicate>
375	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
376	inline _ForwardIterator1
377	find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
378	_ForwardIterator2 __first2, _ForwardIterator2 __last2,
379	_BinaryPredicate __comp)
380	{
381	// concept requirements
382	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
383	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
384	__glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
385	typename iterator_traits<_ForwardIterator1>::value_type,
386	typename iterator_traits<_ForwardIterator2>::value_type>)
387	__glibcxx_requires_valid_range(__first1, __last1);
388	__glibcxx_requires_valid_range(__first2, __last2);
389
390	return std::__find_end(__first1, __last1, __first2, __last2,
391	std::__iterator_category(__first1),
392	std::__iterator_category(__first2),
393	__gnu_cxx::__ops::__iter_comp_iter(__comp));
394	}
395
396	#if __cplusplus >= 201103L
397	/**
398	* @brief Checks that a predicate is true for all the elements
399	* of a sequence.
400	* @ingroup non_mutating_algorithms
401	* @param __first An input iterator.
402	* @param __last An input iterator.
403	* @param __pred A predicate.
404	* @return True if the check is true, false otherwise.
405	*
406	* Returns true if @p __pred is true for each element in the range
407	* @p [__first,__last), and false otherwise.
408	*/
409	template<typename _InputIterator, typename _Predicate>
410	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
411	inline bool
412	all_of(_InputIterator __first, _InputIterator __last, _Predicate __pred)
413	{ return __last == std::find_if_not(__first, __last, __pred); }
414
415	/**
416	* @brief Checks that a predicate is false for all the elements
417	* of a sequence.
418	* @ingroup non_mutating_algorithms
419	* @param __first An input iterator.
420	* @param __last An input iterator.
421	* @param __pred A predicate.
422	* @return True if the check is true, false otherwise.
423	*
424	* Returns true if @p __pred is false for each element in the range
425	* @p [__first,__last), and false otherwise.
426	*/
427	template<typename _InputIterator, typename _Predicate>
428	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
429	inline bool
430	none_of(_InputIterator __first, _InputIterator __last, _Predicate __pred)
431	{ return __last == _GLIBCXX_STD_A::find_if(__first, __last, __pred); }
432
433	/**
434	* @brief Checks that a predicate is true for at least one element
435	* of a sequence.
436	* @ingroup non_mutating_algorithms
437	* @param __first An input iterator.
438	* @param __last An input iterator.
439	* @param __pred A predicate.
440	* @return True if the check is true, false otherwise.
441	*
442	* Returns true if an element exists in the range @p
443	* [__first,__last) such that @p __pred is true, and false
444	* otherwise.
445	*/
446	template<typename _InputIterator, typename _Predicate>
447	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
448	inline bool
449	any_of(_InputIterator __first, _InputIterator __last, _Predicate __pred)
450	{ return !std::none_of(__first, __last, __pred); }
451
452	/**
453	* @brief Find the first element in a sequence for which a
454	* predicate is false.
455	* @ingroup non_mutating_algorithms
456	* @param __first An input iterator.
457	* @param __last An input iterator.
458	* @param __pred A predicate.
459	* @return The first iterator @c i in the range @p [__first,__last)
460	* such that @p __pred(*i) is false, or @p __last if no such iterator exists.
461	*/
462	template<typename _InputIterator, typename _Predicate>
463	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
464	inline _InputIterator
465	find_if_not(_InputIterator __first, _InputIterator __last,
466	_Predicate __pred)
467	{
468	// concept requirements
469	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
470	__glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
471	typename iterator_traits<_InputIterator>::value_type>)
472	__glibcxx_requires_valid_range(__first, __last);
473	return std::__find_if_not(__first, __last,
474	__gnu_cxx::__ops::__pred_iter(__pred));
475	}
476
477	/**
478	* @brief Checks whether the sequence is partitioned.
479	* @ingroup mutating_algorithms
480	* @param __first An input iterator.
481	* @param __last An input iterator.
482	* @param __pred A predicate.
483	* @return True if the range @p [__first,__last) is partioned by @p __pred,
484	* i.e. if all elements that satisfy @p __pred appear before those that
485	* do not.
486	*/
487	template<typename _InputIterator, typename _Predicate>
488	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
489	inline bool
490	is_partitioned(_InputIterator __first, _InputIterator __last,
491	_Predicate __pred)
492	{
493	__first = std::find_if_not(__first, __last, __pred);
494	if (__first == __last)
495	return true;
496	++__first;
497	return std::none_of(__first, __last, __pred);
498	}
499
500	/**
501	* @brief Find the partition point of a partitioned range.
502	* @ingroup mutating_algorithms
503	* @param __first An iterator.
504	* @param __last Another iterator.
505	* @param __pred A predicate.
506	* @return An iterator @p mid such that @p all_of(__first, mid, __pred)
507	* and @p none_of(mid, __last, __pred) are both true.
508	*/
509	template<typename _ForwardIterator, typename _Predicate>
510	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
511	_ForwardIterator
512	partition_point(_ForwardIterator __first, _ForwardIterator __last,
513	_Predicate __pred)
514	{
515	// concept requirements
516	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
517	__glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
518	typename iterator_traits<_ForwardIterator>::value_type>)
519
520	// A specific debug-mode test will be necessary...
521	__glibcxx_requires_valid_range(__first, __last);
522
523	typedef typename iterator_traits<_ForwardIterator>::difference_type
524	_DistanceType;
525
526	_DistanceType __len = std::distance(__first, __last);
527
528	while (__len > `0`)
529	{
530	_DistanceType __half = __len >> `1`;
531	_ForwardIterator __middle = __first;
532	std::advance(__middle, __half);
533	if (__pred(*__middle))
534	{
535	__first = __middle;
536	++__first;
537	__len = __len - __half - `1`;
538	}
539	else
540	__len = __half;
541	}
542	return __first;
543	}
544	#endif
545
546	template<typename _InputIterator, typename _OutputIterator,
547	typename _Predicate>
548	_GLIBCXX20_CONSTEXPR
549	_OutputIterator
550	__remove_copy_if(_InputIterator __first, _InputIterator __last,
551	_OutputIterator __result, _Predicate __pred)
552	{
553	for (; __first != __last; ++__first)
554	if (!__pred(__first))
555	{
556	__result = __first;
557	++__result;
558	}
559	return __result;
560	}
561
562	/**
563	* @brief Copy a sequence, removing elements of a given value.
564	* @ingroup mutating_algorithms
565	* @param __first An input iterator.
566	* @param __last An input iterator.
567	* @param __result An output iterator.
568	* @param __value The value to be removed.
569	* @return An iterator designating the end of the resulting sequence.
570	*
571	* Copies each element in the range @p [__first,__last) not equal
572	* to @p __value to the range beginning at @p __result.
573	* remove_copy() is stable, so the relative order of elements that
574	* are copied is unchanged.
575	*/
576	template<typename _InputIterator, typename _OutputIterator, typename _Tp>
577	_GLIBCXX20_CONSTEXPR
578	inline _OutputIterator
579	remove_copy(_InputIterator __first, _InputIterator __last,
580	_OutputIterator __result, const _Tp& __value)
581	{
582	// concept requirements
583	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
584	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
585	typename iterator_traits<_InputIterator>::value_type>)
586	__glibcxx_function_requires(_EqualOpConcept<
587	typename iterator_traits<_InputIterator>::value_type, _Tp>)
588	__glibcxx_requires_valid_range(__first, __last);
589
590	return std::__remove_copy_if(__first, __last, __result,
591	__gnu_cxx::__ops::__iter_equals_val(__value));
592	}
593
594	/**
595	* @brief Copy a sequence, removing elements for which a predicate is true.
596	* @ingroup mutating_algorithms
597	* @param __first An input iterator.
598	* @param __last An input iterator.
599	* @param __result An output iterator.
600	* @param __pred A predicate.
601	* @return An iterator designating the end of the resulting sequence.
602	*
603	* Copies each element in the range @p [__first,__last) for which
604	* @p __pred returns false to the range beginning at @p __result.
605	*
606	* remove_copy_if() is stable, so the relative order of elements that are
607	* copied is unchanged.
608	*/
609	template<typename _InputIterator, typename _OutputIterator,
610	typename _Predicate>
611	_GLIBCXX20_CONSTEXPR
612	inline _OutputIterator
613	remove_copy_if(_InputIterator __first, _InputIterator __last,
614	_OutputIterator __result, _Predicate __pred)
615	{
616	// concept requirements
617	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
618	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
619	typename iterator_traits<_InputIterator>::value_type>)
620	__glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
621	typename iterator_traits<_InputIterator>::value_type>)
622	__glibcxx_requires_valid_range(__first, __last);
623
624	return std::__remove_copy_if(__first, __last, __result,
625	__gnu_cxx::__ops::__pred_iter(__pred));
626	}
627
628	#if __cplusplus >= 201103L
629	/**
630	* @brief Copy the elements of a sequence for which a predicate is true.
631	* @ingroup mutating_algorithms
632	* @param __first An input iterator.
633	* @param __last An input iterator.
634	* @param __result An output iterator.
635	* @param __pred A predicate.
636	* @return An iterator designating the end of the resulting sequence.
637	*
638	* Copies each element in the range @p [__first,__last) for which
639	* @p __pred returns true to the range beginning at @p __result.
640	*
641	* copy_if() is stable, so the relative order of elements that are
642	* copied is unchanged.
643	*/
644	template<typename _InputIterator, typename _OutputIterator,
645	typename _Predicate>
646	_GLIBCXX20_CONSTEXPR
647	_OutputIterator
648	copy_if(_InputIterator __first, _InputIterator __last,
649	_OutputIterator __result, _Predicate __pred)
650	{
651	// concept requirements
652	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
653	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
654	typename iterator_traits<_InputIterator>::value_type>)
655	__glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
656	typename iterator_traits<_InputIterator>::value_type>)
657	__glibcxx_requires_valid_range(__first, __last);
658
659	for (; __first != __last; ++__first)
660	if (__pred(*__first))
661	{
662	__result = __first;
663	++__result;
664	}
665	return __result;
666	}
667
668	/**
669	* @brief Copies the range [first,first+n) into [result,result+n).
670	* @ingroup mutating_algorithms
671	* @param __first An input iterator.
672	* @param __n The number of elements to copy.
673	* @param __result An output iterator.
674	* @return result+n.
675	*
676	* This inline function will boil down to a call to @c memmove whenever
677	* possible. Failing that, if random access iterators are passed, then the
678	* loop count will be known (and therefore a candidate for compiler
679	* optimizations such as unrolling).
680	*/
681	template<typename _InputIterator, typename _Size, typename _OutputIterator>
682	_GLIBCXX20_CONSTEXPR
683	inline _OutputIterator
684	copy_n(_InputIterator __first, _Size __n, _OutputIterator __result)
685	{
686	// concept requirements
687	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
688	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
689	typename iterator_traits<_InputIterator>::value_type>)
690
691	const auto __n2 = std::__size_to_integer(__n);
692	if (__n2 <= `0`)
693	return __result;
694
695	__glibcxx_requires_can_increment(__first, __n2);
696	__glibcxx_requires_can_increment(__result, __n2);
697
698	auto __res = std::__copy_n_a(std::__niter_base(__first), __n2,
699	std::__niter_base(__result), true);
700	return std::__niter_wrap(__result, std::move(__res));
701	}
702
703	/**
704	* @brief Copy the elements of a sequence to separate output sequences
705	* depending on the truth value of a predicate.
706	* @ingroup mutating_algorithms
707	* @param __first An input iterator.
708	* @param __last An input iterator.
709	* @param __out_true An output iterator.
710	* @param __out_false An output iterator.
711	* @param __pred A predicate.
712	* @return A pair designating the ends of the resulting sequences.
713	*
714	* Copies each element in the range @p [__first,__last) for which
715	* @p __pred returns true to the range beginning at @p out_true
716	* and each element for which @p __pred returns false to @p __out_false.
717	*/
718	template<typename _InputIterator, typename _OutputIterator1,
719	typename _OutputIterator2, typename _Predicate>
720	_GLIBCXX20_CONSTEXPR
721	pair<_OutputIterator1, _OutputIterator2>
722	partition_copy(_InputIterator __first, _InputIterator __last,
723	_OutputIterator1 __out_true, _OutputIterator2 __out_false,
724	_Predicate __pred)
725	{
726	// concept requirements
727	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
728	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator1,
729	typename iterator_traits<_InputIterator>::value_type>)
730	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator2,
731	typename iterator_traits<_InputIterator>::value_type>)
732	__glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
733	typename iterator_traits<_InputIterator>::value_type>)
734	__glibcxx_requires_valid_range(__first, __last);
735
736	for (; __first != __last; ++__first)
737	if (__pred(*__first))
738	{
739	__out_true = __first;
740	++__out_true;
741	}
742	else
743	{
744	__out_false = __first;
745	++__out_false;
746	}
747
748	return pair<_OutputIterator1, _OutputIterator2>(__out_true, __out_false);
749	}
750	#endif // C++11
751
752	/**
753	* @brief Remove elements from a sequence.
754	* @ingroup mutating_algorithms
755	* @param __first An input iterator.
756	* @param __last An input iterator.
757	* @param __value The value to be removed.
758	* @return An iterator designating the end of the resulting sequence.
759	*
760	* All elements equal to @p __value are removed from the range
761	* @p [__first,__last).
762	*
763	* remove() is stable, so the relative order of elements that are
764	* not removed is unchanged.
765	*
766	* Elements between the end of the resulting sequence and @p __last
767	* are still present, but their value is unspecified.
768	*/
769	template<typename _ForwardIterator, typename _Tp>
770	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
771	inline _ForwardIterator
772	remove(_ForwardIterator __first, _ForwardIterator __last,
773	const _Tp& __value)
774	{
775	// concept requirements
776	__glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
777	_ForwardIterator>)
778	__glibcxx_function_requires(_EqualOpConcept<
779	typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
780	__glibcxx_requires_valid_range(__first, __last);
781
782	return std::__remove_if(__first, __last,
783	__gnu_cxx::__ops::__iter_equals_val(__value));
784	}
785
786	/**
787	* @brief Remove elements from a sequence using a predicate.
788	* @ingroup mutating_algorithms
789	* @param __first A forward iterator.
790	* @param __last A forward iterator.
791	* @param __pred A predicate.
792	* @return An iterator designating the end of the resulting sequence.
793	*
794	* All elements for which @p __pred returns true are removed from the range
795	* @p [__first,__last).
796	*
797	* remove_if() is stable, so the relative order of elements that are
798	* not removed is unchanged.
799	*
800	* Elements between the end of the resulting sequence and @p __last
801	* are still present, but their value is unspecified.
802	*/
803	template<typename _ForwardIterator, typename _Predicate>
804	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
805	inline _ForwardIterator
806	remove_if(_ForwardIterator __first, _ForwardIterator __last,
807	_Predicate __pred)
808	{
809	// concept requirements
810	__glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
811	_ForwardIterator>)
812	__glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
813	typename iterator_traits<_ForwardIterator>::value_type>)
814	__glibcxx_requires_valid_range(__first, __last);
815
816	return std::__remove_if(__first, __last,
817	__gnu_cxx::__ops::__pred_iter(__pred));
818	}
819
820	template<typename _ForwardIterator, typename _BinaryPredicate>
821	_GLIBCXX20_CONSTEXPR
822	_ForwardIterator
823	__adjacent_find(_ForwardIterator __first, _ForwardIterator __last,
824	_BinaryPredicate __binary_pred)
825	{
826	if (__first == __last)
827	return __last;
828	_ForwardIterator __next = __first;
829	while (++__next != __last)
830	{
831	if (__binary_pred(__first, __next))
832	return __first;
833	__first = __next;
834	}
835	return __last;
836	}
837
838	template<typename _ForwardIterator, typename _BinaryPredicate>
839	_GLIBCXX20_CONSTEXPR
840	_ForwardIterator
841	__unique(_ForwardIterator __first, _ForwardIterator __last,
842	_BinaryPredicate __binary_pred)
843	{
844	// Skip the beginning, if already unique.
845	__first = std::__adjacent_find(__first, __last, __binary_pred);
846	if (__first == __last)
847	return __last;
848
849	// Do the real copy work.
850	_ForwardIterator __dest = __first;
851	++__first;
852	while (++__first != __last)
853	if (!__binary_pred(__dest, __first))
854	++__dest = _GLIBCXX_MOVE(__first);
855	return ++__dest;
856	}
857
858	/**
859	* @brief Remove consecutive duplicate values from a sequence.
860	* @ingroup mutating_algorithms
861	* @param __first A forward iterator.
862	* @param __last A forward iterator.
863	* @return An iterator designating the end of the resulting sequence.
864	*
865	* Removes all but the first element from each group of consecutive
866	* values that compare equal.
867	* unique() is stable, so the relative order of elements that are
868	* not removed is unchanged.
869	* Elements between the end of the resulting sequence and @p __last
870	* are still present, but their value is unspecified.
871	*/
872	template<typename _ForwardIterator>
873	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
874	inline _ForwardIterator
875	unique(_ForwardIterator __first, _ForwardIterator __last)
876	{
877	// concept requirements
878	__glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
879	_ForwardIterator>)
880	__glibcxx_function_requires(_EqualityComparableConcept<
881	typename iterator_traits<_ForwardIterator>::value_type>)
882	__glibcxx_requires_valid_range(__first, __last);
883
884	return std::__unique(__first, __last,
885	__gnu_cxx::__ops::__iter_equal_to_iter());
886	}
887
888	/**
889	* @brief Remove consecutive values from a sequence using a predicate.
890	* @ingroup mutating_algorithms
891	* @param __first A forward iterator.
892	* @param __last A forward iterator.
893	* @param __binary_pred A binary predicate.
894	* @return An iterator designating the end of the resulting sequence.
895	*
896	* Removes all but the first element from each group of consecutive
897	* values for which @p __binary_pred returns true.
898	* unique() is stable, so the relative order of elements that are
899	* not removed is unchanged.
900	* Elements between the end of the resulting sequence and @p __last
901	* are still present, but their value is unspecified.
902	*/
903	template<typename _ForwardIterator, typename _BinaryPredicate>
904	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
905	inline _ForwardIterator
906	unique(_ForwardIterator __first, _ForwardIterator __last,
907	_BinaryPredicate __binary_pred)
908	{
909	// concept requirements
910	__glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
911	_ForwardIterator>)
912	__glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
913	typename iterator_traits<_ForwardIterator>::value_type,
914	typename iterator_traits<_ForwardIterator>::value_type>)
915	__glibcxx_requires_valid_range(__first, __last);
916
917	return std::__unique(__first, __last,
918	__gnu_cxx::__ops::__iter_comp_iter(__binary_pred));
919	}
920
921	/**
922	* This is an uglified
923	* unique_copy(_InputIterator, _InputIterator, _OutputIterator,
924	* _BinaryPredicate)
925	* overloaded for forward iterators and output iterator as result.
926	*/
927	template<typename _ForwardIterator, typename _OutputIterator,
928	typename _BinaryPredicate>
929	_GLIBCXX20_CONSTEXPR
930	_OutputIterator
931	__unique_copy(_ForwardIterator __first, _ForwardIterator __last,
932	_OutputIterator __result, _BinaryPredicate __binary_pred,
933	forward_iterator_tag, output_iterator_tag)
934	{
935	// concept requirements -- iterators already checked
936	__glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
937	typename iterator_traits<_ForwardIterator>::value_type,
938	typename iterator_traits<_ForwardIterator>::value_type>)
939
940	_ForwardIterator __next = __first;
941	__result = __first;
942	while (++__next != __last)
943	if (!__binary_pred(__first, __next))
944	{
945	__first = __next;
946	++__result = __first;
947	}
948	return ++__result;
949	}
950
951	/**
952	* This is an uglified
953	* unique_copy(_InputIterator, _InputIterator, _OutputIterator,
954	* _BinaryPredicate)
955	* overloaded for input iterators and output iterator as result.
956	*/
957	template<typename _InputIterator, typename _OutputIterator,
958	typename _BinaryPredicate>
959	_GLIBCXX20_CONSTEXPR
960	_OutputIterator
961	__unique_copy(_InputIterator __first, _InputIterator __last,
962	_OutputIterator __result, _BinaryPredicate __binary_pred,
963	input_iterator_tag, output_iterator_tag)
964	{
965	// concept requirements -- iterators already checked
966	__glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
967	typename iterator_traits<_InputIterator>::value_type,
968	typename iterator_traits<_InputIterator>::value_type>)
969
970	typename iterator_traits<_InputIterator>::value_type __value = *__first;
971	__decltype(__gnu_cxx::__ops::__iter_comp_val(__binary_pred))
972	__rebound_pred
973	= __gnu_cxx::__ops::__iter_comp_val(__binary_pred);
974	*__result = __value;
975	while (++__first != __last)
976	if (!__rebound_pred(__first, __value))
977	{
978	__value = *__first;
979	*++__result = __value;
980	}
981	return ++__result;
982	}
983
984	/**
985	* This is an uglified
986	* unique_copy(_InputIterator, _InputIterator, _OutputIterator,
987	* _BinaryPredicate)
988	* overloaded for input iterators and forward iterator as result.
989	*/
990	template<typename _InputIterator, typename _ForwardIterator,
991	typename _BinaryPredicate>
992	_GLIBCXX20_CONSTEXPR
993	_ForwardIterator
994	__unique_copy(_InputIterator __first, _InputIterator __last,
995	_ForwardIterator __result, _BinaryPredicate __binary_pred,
996	input_iterator_tag, forward_iterator_tag)
997	{
998	// concept requirements -- iterators already checked
999	__glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
1000	typename iterator_traits<_ForwardIterator>::value_type,
1001	typename iterator_traits<_InputIterator>::value_type>)
1002	__result = __first;
1003	while (++__first != __last)
1004	if (!__binary_pred(__result, __first))
1005	++__result = __first;
1006	return ++__result;
1007	}
1008
1009	/**
1010	* This is an uglified reverse(_BidirectionalIterator,
1011	* _BidirectionalIterator)
1012	* overloaded for bidirectional iterators.
1013	*/
1014	template<typename _BidirectionalIterator>
1015	_GLIBCXX20_CONSTEXPR
1016	void
1017	__reverse(_BidirectionalIterator __first, _BidirectionalIterator __last,
1018	bidirectional_iterator_tag)
1019	{
1020	while (true)
1021	if (__first == __last \|\| __first == --__last)
1022	return;
1023	else
1024	{
1025	std::iter_swap(__first, __last);
1026	++__first;
1027	}
1028	}
1029
1030	/**
1031	* This is an uglified reverse(_BidirectionalIterator,
1032	* _BidirectionalIterator)
1033	* overloaded for random access iterators.
1034	*/
1035	template<typename _RandomAccessIterator>
1036	_GLIBCXX20_CONSTEXPR
1037	void
1038	__reverse(_RandomAccessIterator __first, _RandomAccessIterator __last,
1039	random_access_iterator_tag)
1040	{
1041	if (__first == __last)
1042	return;
1043	--__last;
1044	while (__first < __last)
1045	{
1046	std::iter_swap(__first, __last);
1047	++__first;
1048	--__last;
1049	}
1050	}
1051
1052	/**
1053	* @brief Reverse a sequence.
1054	* @ingroup mutating_algorithms
1055	* @param __first A bidirectional iterator.
1056	* @param __last A bidirectional iterator.
1057	* @return reverse() returns no value.
1058	*
1059	* Reverses the order of the elements in the range @p [__first,__last),
1060	* so that the first element becomes the last etc.
1061	* For every @c i such that @p 0<=i<=(__last-__first)/2), @p reverse()
1062	* swaps @p (__first+i) and @p (__last-(i+1))
1063	*/
1064	template<typename _BidirectionalIterator>
1065	_GLIBCXX20_CONSTEXPR
1066	inline void
1067	reverse(_BidirectionalIterator __first, _BidirectionalIterator __last)
1068	{
1069	// concept requirements
1070	__glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<
1071	_BidirectionalIterator>)
1072	__glibcxx_requires_valid_range(__first, __last);
1073	std::__reverse(__first, __last, std::__iterator_category(__first));
1074	}
1075
1076	/**
1077	* @brief Copy a sequence, reversing its elements.
1078	* @ingroup mutating_algorithms
1079	* @param __first A bidirectional iterator.
1080	* @param __last A bidirectional iterator.
1081	* @param __result An output iterator.
1082	* @return An iterator designating the end of the resulting sequence.
1083	*
1084	* Copies the elements in the range @p [__first,__last) to the
1085	* range @p [__result,__result+(__last-__first)) such that the
1086	* order of the elements is reversed. For every @c i such that @p
1087	* 0<=i<=(__last-__first), @p reverse_copy() performs the
1088	* assignment @p (__result+(__last-__first)-1-i) = (__first+i).
1089	* The ranges @p [__first,__last) and @p
1090	* [__result,__result+(__last-__first)) must not overlap.
1091	*/
1092	template<typename _BidirectionalIterator, typename _OutputIterator>
1093	_GLIBCXX20_CONSTEXPR
1094	_OutputIterator
1095	reverse_copy(_BidirectionalIterator __first, _BidirectionalIterator __last,
1096	_OutputIterator __result)
1097	{
1098	// concept requirements
1099	__glibcxx_function_requires(_BidirectionalIteratorConcept<
1100	_BidirectionalIterator>)
1101	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
1102	typename iterator_traits<_BidirectionalIterator>::value_type>)
1103	__glibcxx_requires_valid_range(__first, __last);
1104
1105	while (__first != __last)
1106	{
1107	--__last;
1108	__result = __last;
1109	++__result;
1110	}
1111	return __result;
1112	}
1113
1114	/**
1115	* This is a helper function for the rotate algorithm specialized on RAIs.
1116	* It returns the greatest common divisor of two integer values.
1117	*/
1118	template<typename _EuclideanRingElement>
1119	_GLIBCXX20_CONSTEXPR
1120	_EuclideanRingElement
1121	__gcd(_EuclideanRingElement __m, _EuclideanRingElement __n)
1122	{
1123	while (__n != `0`)
1124	{
1125	_EuclideanRingElement __t = __m % __n;
1126	__m = __n;
1127	__n = __t;
1128	}
1129	return __m;
1130	}
1131
1132	_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
1133
1134	/// This is a helper function for the rotate algorithm.
1135	template<typename _ForwardIterator>
1136	_GLIBCXX20_CONSTEXPR
1137	_ForwardIterator
1138	__rotate(_ForwardIterator __first,
1139	_ForwardIterator __middle,
1140	_ForwardIterator __last,
1141	forward_iterator_tag)
1142	{
1143	if (__first == __middle)
1144	return __last;
1145	else if (__last == __middle)
1146	return __first;
1147
1148	_ForwardIterator __first2 = __middle;
1149	do
1150	{
1151	std::iter_swap(__first, __first2);
1152	++__first;
1153	++__first2;
1154	if (__first == __middle)
1155	__middle = __first2;
1156	}
1157	while (__first2 != __last);
1158
1159	_ForwardIterator __ret = __first;
1160
1161	__first2 = __middle;
1162
1163	while (__first2 != __last)
1164	{
1165	std::iter_swap(__first, __first2);
1166	++__first;
1167	++__first2;
1168	if (__first == __middle)
1169	__middle = __first2;
1170	else if (__first2 == __last)
1171	__first2 = __middle;
1172	}
1173	return __ret;
1174	}
1175
1176	/// This is a helper function for the rotate algorithm.
1177	template<typename _BidirectionalIterator>
1178	_GLIBCXX20_CONSTEXPR
1179	_BidirectionalIterator
1180	__rotate(_BidirectionalIterator __first,
1181	_BidirectionalIterator __middle,
1182	_BidirectionalIterator __last,
1183	bidirectional_iterator_tag)
1184	{
1185	// concept requirements
1186	__glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<
1187	_BidirectionalIterator>)
1188
1189	if (__first == __middle)
1190	return __last;
1191	else if (__last == __middle)
1192	return __first;
1193
1194	std::__reverse(__first, __middle, bidirectional_iterator_tag ());
1195	std::__reverse(__middle, __last, bidirectional_iterator_tag ());
1196
1197	while (__first != __middle && __middle != __last)
1198	{
1199	std::iter_swap(__first, --__last);
1200	++__first;
1201	}
1202
1203	if (__first == __middle)
1204	{
1205	std::__reverse(__middle, __last, bidirectional_iterator_tag ());
1206	return __last;
1207	}
1208	else
1209	{
1210	std::__reverse(__first, __middle, bidirectional_iterator_tag ());
1211	return __first;
1212	}
1213	}
1214
1215	/// This is a helper function for the rotate algorithm.
1216	template<typename _RandomAccessIterator>
1217	_GLIBCXX20_CONSTEXPR
1218	_RandomAccessIterator
1219	__rotate(_RandomAccessIterator __first,
1220	_RandomAccessIterator __middle,
1221	_RandomAccessIterator __last,
1222	random_access_iterator_tag)
1223	{
1224	// concept requirements
1225	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
1226	_RandomAccessIterator>)
1227
1228	if (__first == __middle)
1229	return __last;
1230	else if (__last == __middle)
1231	return __first;
1232
1233	typedef typename iterator_traits<_RandomAccessIterator>::difference_type
1234	_Distance;
1235	typedef typename iterator_traits<_RandomAccessIterator>::value_type
1236	_ValueType;
1237
1238	#if __cplusplus >= 201103L
1239	typedef typename make_unsigned<_Distance>::type _UDistance;
1240	#else
1241	typedef _Distance _UDistance;
1242	#endif
1243
1244	_Distance __n = __last - __first;
1245	_Distance __k = __middle - __first;
1246
1247	if (__k == __n - __k)
1248	{
1249	std::swap_ranges(__first, __middle, __middle);
1250	return __middle;
1251	}
1252
1253	_RandomAccessIterator __p = __first;
1254	_RandomAccessIterator __ret = __first + (__last - __middle);
1255
1256	for (;;)
1257	{
1258	if (__k < __n - __k)
1259	{
1260	if (__is_pod(_ValueType) && __k == `1`)
1261	{
1262	_ValueType __t = _GLIBCXX_MOVE(*__p);
1263	_GLIBCXX_MOVE3(__p + `1`, __p + __n, __p);
1264	*(__p + __n - `1`) = _GLIBCXX_MOVE(__t);
1265	return __ret;
1266	}
1267	_RandomAccessIterator __q = __p + __k;
1268	for (_Distance __i = `0`; __i < __n - __k; ++ __i)
1269	{
1270	std::iter_swap(__p, __q);
1271	++__p;
1272	++__q;
1273	}
1274	__n = static_cast<_UDistance>(__n) % static_cast<_UDistance>(__k);
1275	if (__n == `0`)
1276	return __ret;
1277	std::swap(__n, __k);
1278	__k = __n - __k;
1279	}
1280	else
1281	{
1282	__k = __n - __k;
1283	if (__is_pod(_ValueType) && __k == `1`)
1284	{
1285	_ValueType __t = _GLIBCXX_MOVE(*(__p + __n - `1`));
1286	_GLIBCXX_MOVE_BACKWARD3(__p, __p + __n - `1`, __p + __n);
1287	*__p = _GLIBCXX_MOVE(__t);
1288	return __ret;
1289	}
1290	_RandomAccessIterator __q = __p + __n;
1291	__p = __q - __k;
1292	for (_Distance __i = `0`; __i < __n - __k; ++ __i)
1293	{
1294	--__p;
1295	--__q;
1296	std::iter_swap(__p, __q);
1297	}
1298	__n = static_cast<_UDistance>(__n) % static_cast<_UDistance>(__k);
1299	if (__n == `0`)
1300	return __ret;
1301	std::swap(__n, __k);
1302	}
1303	}
1304	}
1305
1306	// _GLIBCXX_RESOLVE_LIB_DEFECTS
1307	// DR 488. rotate throws away useful information
1308	/**
1309	* @brief Rotate the elements of a sequence.
1310	* @ingroup mutating_algorithms
1311	* @param __first A forward iterator.
1312	* @param __middle A forward iterator.
1313	* @param __last A forward iterator.
1314	* @return first + (last - middle).
1315	*
1316	* Rotates the elements of the range @p [__first,__last) by
1317	* @p (__middle - __first) positions so that the element at @p __middle
1318	* is moved to @p __first, the element at @p __middle+1 is moved to
1319	* @p __first+1 and so on for each element in the range
1320	* @p [__first,__last).
1321	*
1322	* This effectively swaps the ranges @p [__first,__middle) and
1323	* @p [__middle,__last).
1324	*
1325	* Performs
1326	* @p (__first+(n+(__last-__middle))%(__last-__first))=(__first+n)
1327	* for each @p n in the range @p [0,__last-__first).
1328	*/
1329	template<typename _ForwardIterator>
1330	_GLIBCXX20_CONSTEXPR
1331	inline _ForwardIterator
1332	rotate(_ForwardIterator __first, _ForwardIterator __middle,
1333	_ForwardIterator __last)
1334	{
1335	// concept requirements
1336	__glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
1337	_ForwardIterator>)
1338	__glibcxx_requires_valid_range(__first, __middle);
1339	__glibcxx_requires_valid_range(__middle, __last);
1340
1341	return std::__rotate(__first, __middle, __last,
1342	std::__iterator_category(__first));
1343	}
1344
1345	_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
1346
1347	/**
1348	* @brief Copy a sequence, rotating its elements.
1349	* @ingroup mutating_algorithms
1350	* @param __first A forward iterator.
1351	* @param __middle A forward iterator.
1352	* @param __last A forward iterator.
1353	* @param __result An output iterator.
1354	* @return An iterator designating the end of the resulting sequence.
1355	*
1356	* Copies the elements of the range @p [__first,__last) to the
1357	* range beginning at @result, rotating the copied elements by
1358	* @p (__middle-__first) positions so that the element at @p __middle
1359	* is moved to @p __result, the element at @p __middle+1 is moved
1360	* to @p __result+1 and so on for each element in the range @p
1361	* [__first,__last).
1362	*
1363	* Performs
1364	* @p (__result+(n+(__last-__middle))%(__last-__first))=(__first+n)
1365	* for each @p n in the range @p [0,__last-__first).
1366	*/
1367	template<typename _ForwardIterator, typename _OutputIterator>
1368	_GLIBCXX20_CONSTEXPR
1369	inline _OutputIterator
1370	rotate_copy(_ForwardIterator __first, _ForwardIterator __middle,
1371	_ForwardIterator __last, _OutputIterator __result)
1372	{
1373	// concept requirements
1374	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
1375	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
1376	typename iterator_traits<_ForwardIterator>::value_type>)
1377	__glibcxx_requires_valid_range(__first, __middle);
1378	__glibcxx_requires_valid_range(__middle, __last);
1379
1380	return std::copy(__first, __middle,
1381	std::copy(__middle, __last, __result));
1382	}
1383
1384	/// This is a helper function...
1385	template<typename _ForwardIterator, typename _Predicate>
1386	_GLIBCXX20_CONSTEXPR
1387	_ForwardIterator
1388	__partition(_ForwardIterator __first, _ForwardIterator __last,
1389	_Predicate __pred, forward_iterator_tag)
1390	{
1391	if (__first == __last)
1392	return __first;
1393
1394	while (__pred(*__first))
1395	if (++__first == __last)
1396	return __first;
1397
1398	_ForwardIterator __next = __first;
1399
1400	while (++__next != __last)
1401	if (__pred(*__next))
1402	{
1403	std::iter_swap(__first, __next);
1404	++__first;
1405	}
1406
1407	return __first;
1408	}
1409
1410	/// This is a helper function...
1411	template<typename _BidirectionalIterator, typename _Predicate>
1412	_GLIBCXX20_CONSTEXPR
1413	_BidirectionalIterator
1414	__partition(_BidirectionalIterator __first, _BidirectionalIterator __last,
1415	_Predicate __pred, bidirectional_iterator_tag)
1416	{
1417	while (true)
1418	{
1419	while (true)
1420	if (__first == __last)
1421	return __first;
1422	else if (__pred(*__first))
1423	++__first;
1424	else
1425	break;
1426	--__last;
1427	while (true)
1428	if (__first == __last)
1429	return __first;
1430	else if (!bool(__pred(*__last)))
1431	--__last;
1432	else
1433	break;
1434	std::iter_swap(__first, __last);
1435	++__first;
1436	}
1437	}
1438
1439	#if _GLIBCXX_HOSTED
1440	// partition
1441
1442	/// This is a helper function...
1443	/// Requires __first != __last and !__pred(__first)
1444	/// and __len == distance(__first, __last).
1445	///
1446	/// !__pred(__first) allows us to guarantee that we don't
1447	/// move-assign an element onto itself.
1448	template<typename _ForwardIterator, typename _Pointer, typename _Predicate,
1449	typename _Distance>
1450	_GLIBCXX26_CONSTEXPR
1451	_ForwardIterator
1452	__stable_partition_adaptive(_ForwardIterator __first,
1453	_ForwardIterator __last,
1454	_Predicate __pred, _Distance __len,
1455	_Pointer __buffer,
1456	_Distance __buffer_size)
1457	{
1458	if (__len == `1`)
1459	return __first;
1460
1461	if (__len <= __buffer_size)
1462	{
1463	_ForwardIterator __result1 = __first;
1464	_Pointer __result2 = __buffer;
1465
1466	// The precondition guarantees that !__pred(__first), so
1467	// move that element to the buffer before starting the loop.
1468	// This ensures that we only call __pred once per element.
1469	__result2 = _GLIBCXX_MOVE(__first);
1470	++__result2;
1471	++__first;
1472	for (; __first != __last; ++__first)
1473	if (__pred(__first))
1474	{
1475	__result1 = _GLIBCXX_MOVE(__first);
1476	++__result1;
1477	}
1478	else
1479	{
1480	__result2 = _GLIBCXX_MOVE(__first);
1481	++__result2;
1482	}
1483
1484	_GLIBCXX_MOVE3(__buffer, __result2, __result1);
1485	return __result1;
1486	}
1487
1488	_ForwardIterator __middle = __first;
1489	std::advance(__middle, __len / `2`);
1490	_ForwardIterator __left_split =
1491	std::__stable_partition_adaptive(__first, __middle, __pred,
1492	__len / `2`, __buffer,
1493	__buffer_size);
1494
1495	// Advance past true-predicate values to satisfy this
1496	// function's preconditions.
1497	_Distance __right_len = __len - __len / `2`;
1498	_ForwardIterator __right_split =
1499	std::__find_if_not_n(__middle, __right_len, __pred);
1500
1501	if (__right_len)
1502	__right_split =
1503	std::__stable_partition_adaptive(__right_split, __last, __pred,
1504	__right_len,
1505	__buffer, __buffer_size);
1506
1507	return std::rotate(__left_split, __middle, __right_split);
1508	}
1509
1510	template<typename _ForwardIterator, typename _Predicate>
1511	_GLIBCXX26_CONSTEXPR
1512	_ForwardIterator
1513	__stable_partition(_ForwardIterator __first, _ForwardIterator __last,
1514	_Predicate __pred)
1515	{
1516	__first = std::__find_if_not(__first, __last, __pred);
1517
1518	if (__first == __last)
1519	return __first;
1520
1521	typedef typename iterator_traits<_ForwardIterator>::value_type
1522	_ValueType;
1523	typedef typename iterator_traits<_ForwardIterator>::difference_type
1524	_DistanceType;
1525
1526	const _DistanceType __len = std::distance(__first, __last);
1527
1528	#if __glibcxx_constexpr_algorithms >= 202306L // >= C++26
1529	if consteval {
1530	// Simulate a _Temporary_buffer of length 1:
1531	_ValueType __buf = std::move(*__first);
1532	*__first = std::move(__buf);
1533	return std::__stable_partition_adaptive(__first, __last, __pred,
1534	__len,
1535	&__buf,
1536	_DistanceType(`1`));
1537	}
1538	#endif
1539
1540	_Temporary_buffer<_ForwardIterator, _ValueType>
1541	__buf(__first, __len);
1542	return
1543	std::__stable_partition_adaptive(__first, __last, __pred,
1544	__len,
1545	__buf.begin(),
1546	_DistanceType(__buf.size()));
1547	}
1548
1549	/**
1550	* @brief Move elements for which a predicate is true to the beginning
1551	* of a sequence, preserving relative ordering.
1552	* @ingroup mutating_algorithms
1553	* @param __first A forward iterator.
1554	* @param __last A forward iterator.
1555	* @param __pred A predicate functor.
1556	* @return An iterator @p middle such that @p __pred(i) is true for each
1557	* iterator @p i in the range @p [first,middle) and false for each @p i
1558	* in the range @p [middle,last).
1559	*
1560	* Performs the same function as @p partition() with the additional
1561	* guarantee that the relative ordering of elements in each group is
1562	* preserved, so any two elements @p x and @p y in the range
1563	* @p [__first,__last) such that @p __pred(x)==__pred(y) will have the same
1564	* relative ordering after calling @p stable_partition().
1565	*/
1566	template<typename _ForwardIterator, typename _Predicate>
1567	_GLIBCXX26_CONSTEXPR
1568	inline _ForwardIterator
1569	stable_partition(_ForwardIterator __first, _ForwardIterator __last,
1570	_Predicate __pred)
1571	{
1572	// concept requirements
1573	__glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
1574	_ForwardIterator>)
1575	__glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
1576	typename iterator_traits<_ForwardIterator>::value_type>)
1577	__glibcxx_requires_valid_range(__first, __last);
1578
1579	return std::__stable_partition(__first, __last,
1580	__gnu_cxx::__ops::__pred_iter(__pred));
1581	}
1582	#endif // HOSTED
1583
1584	/// @cond undocumented
1585
1586	/// This is a helper function for the sort routines.
1587	template<typename _RandomAccessIterator, typename _Compare>
1588	_GLIBCXX20_CONSTEXPR
1589	void
1590	__heap_select(_RandomAccessIterator __first,
1591	_RandomAccessIterator __middle,
1592	_RandomAccessIterator __last, _Compare __comp)
1593	{
1594	std::__make_heap(__first, __middle, __comp);
1595	for (_RandomAccessIterator __i = __middle; __i < __last; ++__i)
1596	if (__comp(__i, __first))
1597	std::__pop_heap(__first, __middle, __i, __comp);
1598	}
1599
1600	// partial_sort
1601
1602	template<typename _InputIterator, typename _RandomAccessIterator,
1603	typename _Compare>
1604	_GLIBCXX20_CONSTEXPR
1605	_RandomAccessIterator
1606	__partial_sort_copy(_InputIterator __first, _InputIterator __last,
1607	_RandomAccessIterator __result_first,
1608	_RandomAccessIterator __result_last,
1609	_Compare __comp)
1610	{
1611	typedef typename iterator_traits<_InputIterator>::value_type
1612	_InputValueType;
1613	typedef iterator_traits<_RandomAccessIterator> _RItTraits;
1614	typedef typename _RItTraits::difference_type _DistanceType;
1615
1616	if (__result_first == __result_last)
1617	return __result_last;
1618	_RandomAccessIterator __result_real_last = __result_first;
1619	while (__first != __last && __result_real_last != __result_last)
1620	{
1621	__result_real_last = __first;
1622	++__result_real_last;
1623	++__first;
1624	}
1625
1626	std::__make_heap(__result_first, __result_real_last, __comp);
1627	while (__first != __last)
1628	{
1629	if (__comp(__first, __result_first))
1630	std::__adjust_heap(__result_first, _DistanceType(`0`),
1631	_DistanceType(__result_real_last
1632	- __result_first),
1633	_InputValueType(*__first), __comp);
1634	++__first;
1635	}
1636	std::__sort_heap(__result_first, __result_real_last, __comp);
1637	return __result_real_last;
1638	}
1639
1640	/// @endcond
1641
1642	/**
1643	* @brief Copy the smallest elements of a sequence.
1644	* @ingroup sorting_algorithms
1645	* @param __first An iterator.
1646	* @param __last Another iterator.
1647	* @param __result_first A random-access iterator.
1648	* @param __result_last Another random-access iterator.
1649	* @return An iterator indicating the end of the resulting sequence.
1650	*
1651	* Copies and sorts the smallest `N` values from the range
1652	* `[__first, __last)` to the range beginning at `__result_first`, where
1653	* the number of elements to be copied, `N`, is the smaller of
1654	* `(__last - __first)` and `(__result_last - __result_first)`.
1655	* After the sort if `i` and `j` are iterators in the range
1656	* `[__result_first,__result_first + N)` such that `i` precedes `j` then
1657	* `j < i` is false.
1658	* The value returned is `__result_first + N`.
1659	*/
1660	template<typename _InputIterator, typename _RandomAccessIterator>
1661	_GLIBCXX20_CONSTEXPR
1662	inline _RandomAccessIterator
1663	partial_sort_copy(_InputIterator __first, _InputIterator __last,
1664	_RandomAccessIterator __result_first,
1665	_RandomAccessIterator __result_last)
1666	{
1667	#ifdef _GLIBCXX_CONCEPT_CHECKS
1668	typedef typename iterator_traits<_InputIterator>::value_type
1669	_InputValueType;
1670	typedef typename iterator_traits<_RandomAccessIterator>::value_type
1671	_OutputValueType;
1672	#endif
1673
1674	// concept requirements
1675	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
1676	__glibcxx_function_requires(_ConvertibleConcept<_InputValueType,
1677	_OutputValueType>)
1678	__glibcxx_function_requires(_LessThanOpConcept<_InputValueType,
1679	_OutputValueType>)
1680	__glibcxx_function_requires(_LessThanComparableConcept<_OutputValueType>)
1681	__glibcxx_requires_valid_range(__first, __last);
1682	__glibcxx_requires_irreflexive(__first, __last);
1683	__glibcxx_requires_valid_range(__result_first, __result_last);
1684
1685	return std::__partial_sort_copy(__first, __last,
1686	__result_first, __result_last,
1687	__gnu_cxx::__ops::__iter_less_iter());
1688	}
1689
1690	/**
1691	* @brief Copy the smallest elements of a sequence using a predicate for
1692	* comparison.
1693	* @ingroup sorting_algorithms
1694	* @param __first An input iterator.
1695	* @param __last Another input iterator.
1696	* @param __result_first A random-access iterator.
1697	* @param __result_last Another random-access iterator.
1698	* @param __comp A comparison functor.
1699	* @return An iterator indicating the end of the resulting sequence.
1700	*
1701	* Copies and sorts the smallest `N` values from the range
1702	* `[__first, __last)` to the range beginning at `result_first`, where
1703	* the number of elements to be copied, `N`, is the smaller of
1704	* `(__last - __first)` and `(__result_last - __result_first)`.
1705	* After the sort if `i` and `j` are iterators in the range
1706	* `[__result_first, __result_first + N)` such that `i` precedes `j` then
1707	* `__comp(j, i)` is false.
1708	* The value returned is `__result_first + N`.
1709	*/
1710	template<typename _InputIterator, typename _RandomAccessIterator,
1711	typename _Compare>
1712	_GLIBCXX20_CONSTEXPR
1713	inline _RandomAccessIterator
1714	partial_sort_copy(_InputIterator __first, _InputIterator __last,
1715	_RandomAccessIterator __result_first,
1716	_RandomAccessIterator __result_last,
1717	_Compare __comp)
1718	{
1719	#ifdef _GLIBCXX_CONCEPT_CHECKS
1720	typedef typename iterator_traits<_InputIterator>::value_type
1721	_InputValueType;
1722	typedef typename iterator_traits<_RandomAccessIterator>::value_type
1723	_OutputValueType;
1724	#endif
1725
1726	// concept requirements
1727	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
1728	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
1729	_RandomAccessIterator>)
1730	__glibcxx_function_requires(_ConvertibleConcept<_InputValueType,
1731	_OutputValueType>)
1732	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
1733	_InputValueType, _OutputValueType>)
1734	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
1735	_OutputValueType, _OutputValueType>)
1736	__glibcxx_requires_valid_range(__first, __last);
1737	__glibcxx_requires_irreflexive_pred(__first, __last, __comp);
1738	__glibcxx_requires_valid_range(__result_first, __result_last);
1739
1740	return std::__partial_sort_copy(__first, __last,
1741	__result_first, __result_last,
1742	__gnu_cxx::__ops::__iter_comp_iter(__comp));
1743	}
1744
1745	/// @cond undocumented
1746
1747	/// This is a helper function for the sort routine.
1748	template<typename _RandomAccessIterator, typename _Compare>
1749	_GLIBCXX20_CONSTEXPR
1750	void
1751	__unguarded_linear_insert(_RandomAccessIterator __last,
1752	_Compare __comp)
1753	{
1754	typename iterator_traits<_RandomAccessIterator>::value_type
1755	__val = _GLIBCXX_MOVE(*__last);
1756	_RandomAccessIterator __next = __last;
1757	--__next;
1758	while (__comp(__val, __next))
1759	{
1760	__last = _GLIBCXX_MOVE(__next);
1761	__last = __next;
1762	--__next;
1763	}
1764	*__last = _GLIBCXX_MOVE(__val);
1765	}
1766
1767	/// This is a helper function for the sort routine.
1768	template<typename _RandomAccessIterator, typename _Compare>
1769	_GLIBCXX20_CONSTEXPR
1770	void
1771	__insertion_sort(_RandomAccessIterator __first,
1772	_RandomAccessIterator __last, _Compare __comp)
1773	{
1774	if (__first == __last) return;
1775
1776	for (_RandomAccessIterator __i = __first + `1`; __i != __last; ++__i)
1777	{
1778	if (__comp(__i, __first))
1779	{
1780	typename iterator_traits<_RandomAccessIterator>::value_type
1781	__val = _GLIBCXX_MOVE(*__i);
1782	_GLIBCXX_MOVE_BACKWARD3(__first, __i, __i + `1`);
1783	*__first = _GLIBCXX_MOVE(__val);
1784	}
1785	else
1786	std::__unguarded_linear_insert(__i,
1787	__gnu_cxx::__ops::__val_comp_iter(__comp));
1788	}
1789	}
1790
1791	/// This is a helper function for the sort routine.
1792	template<typename _RandomAccessIterator, typename _Compare>
1793	_GLIBCXX20_CONSTEXPR
1794	inline void
1795	__unguarded_insertion_sort(_RandomAccessIterator __first,
1796	_RandomAccessIterator __last, _Compare __comp)
1797	{
1798	for (_RandomAccessIterator __i = __first; __i != __last; ++__i)
1799	std::__unguarded_linear_insert(__i,
1800	__gnu_cxx::__ops::__val_comp_iter(__comp));
1801	}
1802
1803	/**
1804	* @doctodo
1805	* This controls some aspect of the sort routines.
1806	*/
1807	enum { _S_threshold = `16` };
1808
1809	/// This is a helper function for the sort routine.
1810	template<typename _RandomAccessIterator, typename _Compare>
1811	_GLIBCXX20_CONSTEXPR
1812	void
1813	__final_insertion_sort(_RandomAccessIterator __first,
1814	_RandomAccessIterator __last, _Compare __comp)
1815	{
1816	if (__last - __first > int(_S_threshold))
1817	{
1818	std::__insertion_sort(__first, __first + int(_S_threshold), __comp);
1819	std::__unguarded_insertion_sort(__first + int(_S_threshold), __last,
1820	__comp);
1821	}
1822	else
1823	std::__insertion_sort(__first, __last, __comp);
1824	}
1825
1826	/// This is a helper function...
1827	template<typename _RandomAccessIterator, typename _Compare>
1828	_GLIBCXX20_CONSTEXPR
1829	_RandomAccessIterator
1830	__unguarded_partition(_RandomAccessIterator __first,
1831	_RandomAccessIterator __last,
1832	_RandomAccessIterator __pivot, _Compare __comp)
1833	{
1834	while (true)
1835	{
1836	while (__comp(__first, __pivot))
1837	++__first;
1838	--__last;
1839	while (__comp(__pivot, __last))
1840	--__last;
1841	if (!(__first < __last))
1842	return __first;
1843	std::iter_swap(__first, __last);
1844	++__first;
1845	}
1846	}
1847
1848	/// This is a helper function...
1849	template<typename _RandomAccessIterator, typename _Compare>
1850	_GLIBCXX20_CONSTEXPR
1851	inline _RandomAccessIterator
1852	__unguarded_partition_pivot(_RandomAccessIterator __first,
1853	_RandomAccessIterator __last, _Compare __comp)
1854	{
1855	_RandomAccessIterator __mid = __first + (__last - __first) / `2`;
1856	std::__move_median_to_first(__first, __first + `1`, __mid, __last - `1`,
1857	__comp);
1858	return std::__unguarded_partition(__first + `1`, __last, __first, __comp);
1859	}
1860
1861	template<typename _RandomAccessIterator, typename _Compare>
1862	_GLIBCXX20_CONSTEXPR
1863	inline void
1864	__partial_sort(_RandomAccessIterator __first,
1865	_RandomAccessIterator __middle,
1866	_RandomAccessIterator __last,
1867	_Compare __comp)
1868	{
1869	std::__heap_select(__first, __middle, __last, __comp);
1870	std::__sort_heap(__first, __middle, __comp);
1871	}
1872
1873	/// This is a helper function for the sort routine.
1874	template<typename _RandomAccessIterator, typename _Size, typename _Compare>
1875	_GLIBCXX20_CONSTEXPR
1876	void
1877	__introsort_loop(_RandomAccessIterator __first,
1878	_RandomAccessIterator __last,
1879	_Size __depth_limit, _Compare __comp)
1880	{
1881	while (__last - __first > int(_S_threshold))
1882	{
1883	if (__depth_limit == `0`)
1884	{
1885	std::__partial_sort(__first, __last, __last, __comp);
1886	return;
1887	}
1888	--__depth_limit;
1889	_RandomAccessIterator __cut =
1890	std::__unguarded_partition_pivot(__first, __last, __comp);
1891	std::__introsort_loop(__cut, __last, __depth_limit, __comp);
1892	__last = __cut;
1893	}
1894	}
1895
1896	// sort
1897
1898	template<typename _RandomAccessIterator, typename _Compare>
1899	_GLIBCXX20_CONSTEXPR
1900	inline void
1901	__sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
1902	_Compare __comp)
1903	{
1904	if (__first != __last)
1905	{
1906	std::__introsort_loop(__first, __last,
1907	std::__lg(__last - __first) * `2`,
1908	__comp);
1909	std::__final_insertion_sort(__first, __last, __comp);
1910	}
1911	}
1912
1913	template<typename _RandomAccessIterator, typename _Size, typename _Compare>
1914	_GLIBCXX20_CONSTEXPR
1915	void
1916	__introselect(_RandomAccessIterator __first, _RandomAccessIterator __nth,
1917	_RandomAccessIterator __last, _Size __depth_limit,
1918	_Compare __comp)
1919	{
1920	while (__last - __first > `3`)
1921	{
1922	if (__depth_limit == `0`)
1923	{
1924	std::__heap_select(__first, __nth + `1`, __last, __comp);
1925	// Place the nth largest element in its final position.
1926	std::iter_swap(__first, __nth);
1927	return;
1928	}
1929	--__depth_limit;
1930	_RandomAccessIterator __cut =
1931	std::__unguarded_partition_pivot(__first, __last, __comp);
1932	if (__cut <= __nth)
1933	__first = __cut;
1934	else
1935	__last = __cut;
1936	}
1937	std::__insertion_sort(__first, __last, __comp);
1938	}
1939
1940	/// @endcond
1941
1942	// nth_element
1943
1944	// lower_bound moved to stl_algobase.h
1945
1946	/**
1947	* @brief Finds the first position in which `__val` could be inserted
1948	* without changing the ordering.
1949	* @ingroup binary_search_algorithms
1950	* @param __first An iterator to the start of a sorted range.
1951	* @param __last A past-the-end iterator for the sorted range.
1952	* @param __val The search term.
1953	* @param __comp A functor to use for comparisons.
1954	* @return An iterator pointing to the first element _not less than_
1955	* `__val`, or `end()` if every element is less than `__val`.
1956	* @ingroup binary_search_algorithms
1957	*
1958	* The comparison function should have the same effects on ordering as
1959	* the function used for the initial sort.
1960	*/
1961	template<typename _ForwardIterator, typename _Tp, typename _Compare>
1962	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
1963	inline _ForwardIterator
1964	lower_bound(_ForwardIterator __first, _ForwardIterator __last,
1965	const _Tp& __val, _Compare __comp)
1966	{
1967	// concept requirements
1968	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
1969	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
1970	typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
1971	__glibcxx_requires_partitioned_lower_pred(__first, __last,
1972	__val, __comp);
1973
1974	return std::__lower_bound(__first, __last, __val,
1975	__gnu_cxx::__ops::__iter_comp_val(__comp));
1976	}
1977
1978	template<typename _ForwardIterator, typename _Tp, typename _Compare>
1979	_GLIBCXX20_CONSTEXPR
1980	_ForwardIterator
1981	__upper_bound(_ForwardIterator __first, _ForwardIterator __last,
1982	const _Tp& __val, _Compare __comp)
1983	{
1984	typedef typename iterator_traits<_ForwardIterator>::difference_type
1985	_DistanceType;
1986
1987	_DistanceType __len = std::distance(__first, __last);
1988
1989	while (__len > `0`)
1990	{
1991	_DistanceType __half = __len >> `1`;
1992	_ForwardIterator __middle = __first;
1993	std::advance(__middle, __half);
1994	if (__comp(__val, __middle))
1995	__len = __half;
1996	else
1997	{
1998	__first = __middle;
1999	++__first;
2000	__len = __len - __half - `1`;
2001	}
2002	}
2003	return __first;
2004	}
2005
2006	/**
2007	* @brief Finds the last position in which @p __val could be inserted
2008	* without changing the ordering.
2009	* @ingroup binary_search_algorithms
2010	* @param __first An iterator.
2011	* @param __last Another iterator.
2012	* @param __val The search term.
2013	* @return An iterator pointing to the first element greater than @p __val,
2014	* or end() if no elements are greater than @p __val.
2015	* @ingroup binary_search_algorithms
2016	*/
2017	template<typename _ForwardIterator, typename _Tp>
2018	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
2019	inline _ForwardIterator
2020	upper_bound(_ForwardIterator __first, _ForwardIterator __last,
2021	const _Tp& __val)
2022	{
2023	// concept requirements
2024	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2025	__glibcxx_function_requires(_LessThanOpConcept<
2026	_Tp, typename iterator_traits<_ForwardIterator>::value_type>)
2027	__glibcxx_requires_partitioned_upper(__first, __last, __val);
2028
2029	return std::__upper_bound(__first, __last, __val,
2030	__gnu_cxx::__ops::__val_less_iter());
2031	}
2032
2033	/**
2034	* @brief Finds the last position in which @p __val could be inserted
2035	* without changing the ordering.
2036	* @ingroup binary_search_algorithms
2037	* @param __first An iterator.
2038	* @param __last Another iterator.
2039	* @param __val The search term.
2040	* @param __comp A functor to use for comparisons.
2041	* @return An iterator pointing to the first element greater than @p __val,
2042	* or end() if no elements are greater than @p __val.
2043	* @ingroup binary_search_algorithms
2044	*
2045	* The comparison function should have the same effects on ordering as
2046	* the function used for the initial sort.
2047	*/
2048	template<typename _ForwardIterator, typename _Tp, typename _Compare>
2049	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
2050	inline _ForwardIterator
2051	upper_bound(_ForwardIterator __first, _ForwardIterator __last,
2052	const _Tp& __val, _Compare __comp)
2053	{
2054	// concept requirements
2055	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2056	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2057	_Tp, typename iterator_traits<_ForwardIterator>::value_type>)
2058	__glibcxx_requires_partitioned_upper_pred(__first, __last,
2059	__val, __comp);
2060
2061	return std::__upper_bound(__first, __last, __val,
2062	__gnu_cxx::__ops::__val_comp_iter(__comp));
2063	}
2064
2065	template<typename _ForwardIterator, typename _Tp,
2066	typename _CompareItTp, typename _CompareTpIt>
2067	_GLIBCXX20_CONSTEXPR
2068	pair<_ForwardIterator, _ForwardIterator>
2069	__equal_range(_ForwardIterator __first, _ForwardIterator __last,
2070	const _Tp& __val,
2071	_CompareItTp __comp_it_val, _CompareTpIt __comp_val_it)
2072	{
2073	typedef typename iterator_traits<_ForwardIterator>::difference_type
2074	_DistanceType;
2075
2076	_DistanceType __len = std::distance(__first, __last);
2077
2078	while (__len > `0`)
2079	{
2080	_DistanceType __half = __len >> `1`;
2081	_ForwardIterator __middle = __first;
2082	std::advance(__middle, __half);
2083	if (__comp_it_val(__middle, __val))
2084	{
2085	__first = __middle;
2086	++__first;
2087	__len = __len - __half - `1`;
2088	}
2089	else if (__comp_val_it(__val, __middle))
2090	__len = __half;
2091	else
2092	{
2093	_ForwardIterator __left
2094	= std::__lower_bound(__first, __middle, __val, __comp_it_val);
2095	std::advance(__first, __len);
2096	_ForwardIterator __right
2097	= std::__upper_bound(++__middle, __first, __val, __comp_val_it);
2098	return pair<_ForwardIterator, _ForwardIterator>(__left, __right);
2099	}
2100	}
2101	return pair<_ForwardIterator, _ForwardIterator>(__first, __first);
2102	}
2103
2104	/**
2105	* @brief Finds the largest subrange in which @p __val could be inserted
2106	* at any place in it without changing the ordering.
2107	* @ingroup binary_search_algorithms
2108	* @param __first An iterator.
2109	* @param __last Another iterator.
2110	* @param __val The search term.
2111	* @return An pair of iterators defining the subrange.
2112	* @ingroup binary_search_algorithms
2113	*
2114	* This is equivalent to
2115	* @code
2116	* std::make_pair(lower_bound(__first, __last, __val),
2117	* upper_bound(__first, __last, __val))
2118	* @endcode
2119	* but does not actually call those functions.
2120	*/
2121	template<typename _ForwardIterator, typename _Tp>
2122	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
2123	inline pair<_ForwardIterator, _ForwardIterator>
2124	equal_range(_ForwardIterator __first, _ForwardIterator __last,
2125	const _Tp& __val)
2126	{
2127	// concept requirements
2128	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2129	__glibcxx_function_requires(_LessThanOpConcept<
2130	typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
2131	__glibcxx_function_requires(_LessThanOpConcept<
2132	_Tp, typename iterator_traits<_ForwardIterator>::value_type>)
2133	__glibcxx_requires_partitioned_lower(__first, __last, __val);
2134	__glibcxx_requires_partitioned_upper(__first, __last, __val);
2135
2136	return std::__equal_range(__first, __last, __val,
2137	__gnu_cxx::__ops::__iter_less_val(),
2138	__gnu_cxx::__ops::__val_less_iter());
2139	}
2140
2141	/**
2142	* @brief Finds the largest subrange in which @p __val could be inserted
2143	* at any place in it without changing the ordering.
2144	* @param __first An iterator.
2145	* @param __last Another iterator.
2146	* @param __val The search term.
2147	* @param __comp A functor to use for comparisons.
2148	* @return An pair of iterators defining the subrange.
2149	* @ingroup binary_search_algorithms
2150	*
2151	* This is equivalent to
2152	* @code
2153	* std::make_pair(lower_bound(__first, __last, __val, __comp),
2154	* upper_bound(__first, __last, __val, __comp))
2155	* @endcode
2156	* but does not actually call those functions.
2157	*/
2158	template<typename _ForwardIterator, typename _Tp, typename _Compare>
2159	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
2160	inline pair<_ForwardIterator, _ForwardIterator>
2161	equal_range(_ForwardIterator __first, _ForwardIterator __last,
2162	const _Tp& __val, _Compare __comp)
2163	{
2164	// concept requirements
2165	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2166	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2167	typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
2168	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2169	_Tp, typename iterator_traits<_ForwardIterator>::value_type>)
2170	__glibcxx_requires_partitioned_lower_pred(__first, __last,
2171	__val, __comp);
2172	__glibcxx_requires_partitioned_upper_pred(__first, __last,
2173	__val, __comp);
2174
2175	return std::__equal_range(__first, __last, __val,
2176	__gnu_cxx::__ops::__iter_comp_val(__comp),
2177	__gnu_cxx::__ops::__val_comp_iter(__comp));
2178	}
2179
2180	/**
2181	* @brief Determines whether an element exists in a range.
2182	* @ingroup binary_search_algorithms
2183	* @param __first An iterator.
2184	* @param __last Another iterator.
2185	* @param __val The search term.
2186	* @return True if @p __val (or its equivalent) is in [@p
2187	* __first,@p __last ].
2188	*
2189	* Note that this does not actually return an iterator to @p __val. For
2190	* that, use std::find or a container's specialized find member functions.
2191	*/
2192	template<typename _ForwardIterator, typename _Tp>
2193	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
2194	bool
2195	binary_search(_ForwardIterator __first, _ForwardIterator __last,
2196	const _Tp& __val)
2197	{
2198	// concept requirements
2199	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2200	__glibcxx_function_requires(_LessThanOpConcept<
2201	_Tp, typename iterator_traits<_ForwardIterator>::value_type>)
2202	__glibcxx_requires_partitioned_lower(__first, __last, __val);
2203	__glibcxx_requires_partitioned_upper(__first, __last, __val);
2204
2205	_ForwardIterator __i
2206	= std::__lower_bound(__first, __last, __val,
2207	__gnu_cxx::__ops::__iter_less_val());
2208	return __i != __last && !(__val < *__i);
2209	}
2210
2211	/**
2212	* @brief Determines whether an element exists in a range.
2213	* @ingroup binary_search_algorithms
2214	* @param __first An iterator.
2215	* @param __last Another iterator.
2216	* @param __val The search term.
2217	* @param __comp A functor to use for comparisons.
2218	* @return True if @p __val (or its equivalent) is in @p [__first,__last].
2219	*
2220	* Note that this does not actually return an iterator to @p __val. For
2221	* that, use std::find or a container's specialized find member functions.
2222	*
2223	* The comparison function should have the same effects on ordering as
2224	* the function used for the initial sort.
2225	*/
2226	template<typename _ForwardIterator, typename _Tp, typename _Compare>
2227	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
2228	bool
2229	binary_search(_ForwardIterator __first, _ForwardIterator __last,
2230	const _Tp& __val, _Compare __comp)
2231	{
2232	// concept requirements
2233	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2234	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2235	_Tp, typename iterator_traits<_ForwardIterator>::value_type>)
2236	__glibcxx_requires_partitioned_lower_pred(__first, __last,
2237	__val, __comp);
2238	__glibcxx_requires_partitioned_upper_pred(__first, __last,
2239	__val, __comp);
2240
2241	_ForwardIterator __i
2242	= std::__lower_bound(__first, __last, __val,
2243	__gnu_cxx::__ops::__iter_comp_val(__comp));
2244	return __i != __last && !bool(__comp(__val, *__i));
2245	}
2246
2247	// merge
2248
2249	/// This is a helper function for the __merge_adaptive routines.
2250	template<typename _InputIterator1, typename _InputIterator2,
2251	typename _OutputIterator, typename _Compare>
2252	void
2253	__move_merge_adaptive(_InputIterator1 __first1, _InputIterator1 __last1,
2254	_InputIterator2 __first2, _InputIterator2 __last2,
2255	_OutputIterator __result, _Compare __comp)
2256	{
2257	while (__first1 != __last1 && __first2 != __last2)
2258	{
2259	if (__comp(__first2, __first1))
2260	{
2261	__result = _GLIBCXX_MOVE(__first2);
2262	++__first2;
2263	}
2264	else
2265	{
2266	__result = _GLIBCXX_MOVE(__first1);
2267	++__first1;
2268	}
2269	++__result;
2270	}
2271	if (__first1 != __last1)
2272	_GLIBCXX_MOVE3(__first1, __last1, __result);
2273	}
2274
2275	/// This is a helper function for the __merge_adaptive routines.
2276	template<typename _BidirectionalIterator1, typename _BidirectionalIterator2,
2277	typename _BidirectionalIterator3, typename _Compare>
2278	void
2279	__move_merge_adaptive_backward(_BidirectionalIterator1 __first1,
2280	_BidirectionalIterator1 __last1,
2281	_BidirectionalIterator2 __first2,
2282	_BidirectionalIterator2 __last2,
2283	_BidirectionalIterator3 __result,
2284	_Compare __comp)
2285	{
2286	if (__first1 == __last1)
2287	{
2288	_GLIBCXX_MOVE_BACKWARD3(__first2, __last2, __result);
2289	return;
2290	}
2291	else if (__first2 == __last2)
2292	return;
2293
2294	--__last1;
2295	--__last2;
2296	while (true)
2297	{
2298	if (__comp(__last2, __last1))
2299	{
2300	--__result = _GLIBCXX_MOVE(__last1);
2301	if (__first1 == __last1)
2302	{
2303	_GLIBCXX_MOVE_BACKWARD3(__first2, ++__last2, __result);
2304	return;
2305	}
2306	--__last1;
2307	}
2308	else
2309	{
2310	--__result = _GLIBCXX_MOVE(__last2);
2311	if (__first2 == __last2)
2312	return;
2313	--__last2;
2314	}
2315	}
2316	}
2317
2318	/// This is a helper function for the merge routines.
2319	template<typename _BidirectionalIterator1, typename _BidirectionalIterator2,
2320	typename _Distance>
2321	_BidirectionalIterator1
2322	__rotate_adaptive(_BidirectionalIterator1 __first,
2323	_BidirectionalIterator1 __middle,
2324	_BidirectionalIterator1 __last,
2325	_Distance __len1, _Distance __len2,
2326	_BidirectionalIterator2 __buffer,
2327	_Distance __buffer_size)
2328	{
2329	_BidirectionalIterator2 __buffer_end;
2330	if (__len1 > __len2 && __len2 <= __buffer_size)
2331	{
2332	if (__len2)
2333	{
2334	__buffer_end = _GLIBCXX_MOVE3(__middle, __last, __buffer);
2335	_GLIBCXX_MOVE_BACKWARD3(__first, __middle, __last);
2336	return _GLIBCXX_MOVE3(__buffer, __buffer_end, __first);
2337	}
2338	else
2339	return __first;
2340	}
2341	else if (__len1 <= __buffer_size)
2342	{
2343	if (__len1)
2344	{
2345	__buffer_end = _GLIBCXX_MOVE3(__first, __middle, __buffer);
2346	_GLIBCXX_MOVE3(__middle, __last, __first);
2347	return _GLIBCXX_MOVE_BACKWARD3(__buffer, __buffer_end, __last);
2348	}
2349	else
2350	return __last;
2351	}
2352	else
2353	return std::rotate(__first, __middle, __last);
2354	}
2355
2356	/// This is a helper function for the merge routines.
2357	template<typename _BidirectionalIterator, typename _Distance,
2358	typename _Pointer, typename _Compare>
2359	void
2360	__merge_adaptive(_BidirectionalIterator __first,
2361	_BidirectionalIterator __middle,
2362	_BidirectionalIterator __last,
2363	_Distance __len1, _Distance __len2,
2364	_Pointer __buffer, _Compare __comp)
2365	{
2366	if (__len1 <= __len2)
2367	{
2368	_Pointer __buffer_end = _GLIBCXX_MOVE3(__first, __middle, __buffer);
2369	std::__move_merge_adaptive(__buffer, __buffer_end, __middle, __last,
2370	__first, __comp);
2371	}
2372	else
2373	{
2374	_Pointer __buffer_end = _GLIBCXX_MOVE3(__middle, __last, __buffer);
2375	std::__move_merge_adaptive_backward(__first, __middle, __buffer,
2376	__buffer_end, __last, __comp);
2377	}
2378	}
2379
2380	template<typename _BidirectionalIterator, typename _Distance,
2381	typename _Pointer, typename _Compare>
2382	void
2383	__merge_adaptive_resize(_BidirectionalIterator __first,
2384	_BidirectionalIterator __middle,
2385	_BidirectionalIterator __last,
2386	_Distance __len1, _Distance __len2,
2387	_Pointer __buffer, _Distance __buffer_size,
2388	_Compare __comp)
2389	{
2390	if (__len1 <= __buffer_size \|\| __len2 <= __buffer_size)
2391	std::__merge_adaptive(__first, __middle, __last,
2392	__len1, __len2, __buffer, __comp);
2393	else
2394	{
2395	_BidirectionalIterator __first_cut = __first;
2396	_BidirectionalIterator __second_cut = __middle;
2397	_Distance __len11 = `0`;
2398	_Distance __len22 = `0`;
2399	if (__len1 > __len2)
2400	{
2401	__len11 = __len1 / `2`;
2402	std::advance(__first_cut, __len11);
2403	__second_cut
2404	= std::__lower_bound(__middle, __last, *__first_cut,
2405	__gnu_cxx::__ops::__iter_comp_val(__comp));
2406	__len22 = std::distance(__middle, __second_cut);
2407	}
2408	else
2409	{
2410	__len22 = __len2 / `2`;
2411	std::advance(__second_cut, __len22);
2412	__first_cut
2413	= std::__upper_bound(__first, __middle, *__second_cut,
2414	__gnu_cxx::__ops::__val_comp_iter(__comp));
2415	__len11 = std::distance(__first, __first_cut);
2416	}
2417
2418	_BidirectionalIterator __new_middle
2419	= std::__rotate_adaptive(__first_cut, __middle, __second_cut,
2420	_Distance(__len1 - __len11), __len22,
2421	__buffer, __buffer_size);
2422	std::__merge_adaptive_resize(__first, __first_cut, __new_middle,
2423	__len11, __len22,
2424	__buffer, __buffer_size, __comp);
2425	std::__merge_adaptive_resize(__new_middle, __second_cut, __last,
2426	_Distance(__len1 - __len11),
2427	_Distance(__len2 - __len22),
2428	__buffer, __buffer_size, __comp);
2429	}
2430	}
2431
2432	/// This is a helper function for the merge routines.
2433	template<typename _BidirectionalIterator, typename _Distance,
2434	typename _Compare>
2435	_GLIBCXX26_CONSTEXPR
2436	void
2437	__merge_without_buffer(_BidirectionalIterator __first,
2438	_BidirectionalIterator __middle,
2439	_BidirectionalIterator __last,
2440	_Distance __len1, _Distance __len2,
2441	_Compare __comp)
2442	{
2443	if (__len1 == `0` \|\| __len2 == `0`)
2444	return;
2445
2446	if (__len1 + __len2 == `2`)
2447	{
2448	if (__comp(__middle, __first))
2449	std::iter_swap(__first, __middle);
2450	return;
2451	}
2452
2453	_BidirectionalIterator __first_cut = __first;
2454	_BidirectionalIterator __second_cut = __middle;
2455	_Distance __len11 = `0`;
2456	_Distance __len22 = `0`;
2457	if (__len1 > __len2)
2458	{
2459	__len11 = __len1 / `2`;
2460	std::advance(__first_cut, __len11);
2461	__second_cut
2462	= std::__lower_bound(__middle, __last, *__first_cut,
2463	__gnu_cxx::__ops::__iter_comp_val(__comp));
2464	__len22 = std::distance(__middle, __second_cut);
2465	}
2466	else
2467	{
2468	__len22 = __len2 / `2`;
2469	std::advance(__second_cut, __len22);
2470	__first_cut
2471	= std::__upper_bound(__first, __middle, *__second_cut,
2472	__gnu_cxx::__ops::__val_comp_iter(__comp));
2473	__len11 = std::distance(__first, __first_cut);
2474	}
2475
2476	_BidirectionalIterator __new_middle
2477	= std::rotate(__first_cut, __middle, __second_cut);
2478	std::__merge_without_buffer(__first, __first_cut, __new_middle,
2479	__len11, __len22, __comp);
2480	std::__merge_without_buffer(__new_middle, __second_cut, __last,
2481	__len1 - __len11, __len2 - __len22, __comp);
2482	}
2483
2484	template<typename _BidirectionalIterator, typename _Compare>
2485	_GLIBCXX26_CONSTEXPR
2486	void
2487	__inplace_merge(_BidirectionalIterator __first,
2488	_BidirectionalIterator __middle,
2489	_BidirectionalIterator __last,
2490	_Compare __comp)
2491	{
2492	typedef typename iterator_traits<_BidirectionalIterator>::value_type
2493	_ValueType;
2494	typedef typename iterator_traits<_BidirectionalIterator>::difference_type
2495	_DistanceType;
2496
2497	if (__first == __middle \|\| __middle == __last)
2498	return;
2499
2500	const _DistanceType __len1 = std::distance(__first, __middle);
2501	const _DistanceType __len2 = std::distance(__middle, __last);
2502
2503	#if _GLIBCXX_HOSTED
2504	# if __glibcxx_constexpr_algorithms >= 202306L // >= C++26
2505	if consteval {
2506	return std::__merge_without_buffer
2507	(__first, __middle, __last, __len1, __len2, __comp);
2508	}
2509	# endif
2510	typedef _Temporary_buffer<_BidirectionalIterator, _ValueType> _TmpBuf;
2511	// __merge_adaptive will use a buffer for the smaller of
2512	// [first,middle) and [middle,last).
2513	_TmpBuf __buf(__first, std::min(__len1, __len2));
2514
2515	if (__builtin_expect(__buf.size() == __buf.requested_size(), true))
2516	std::__merge_adaptive
2517	(__first, __middle, __last, __len1, __len2, __buf.begin(), __comp);
2518	else if (__builtin_expect(__buf.begin() == `0`, false))
2519	std::__merge_without_buffer
2520	(__first, __middle, __last, __len1, __len2, __comp);
2521	else
2522	std::__merge_adaptive_resize
2523	(__first, __middle, __last, __len1, __len2, __buf.begin(),
2524	_DistanceType(__buf.size()), __comp);
2525	#else
2526	std::__merge_without_buffer
2527	(__first, __middle, __last, __len1, __len2, __comp);
2528	#endif
2529	}
2530
2531	/**
2532	* @brief Merges two sorted ranges in place.
2533	* @ingroup sorting_algorithms
2534	* @param __first An iterator.
2535	* @param __middle Another iterator.
2536	* @param __last Another iterator.
2537	* @return Nothing.
2538	*
2539	* Merges two sorted and consecutive ranges, [__first,__middle) and
2540	* [__middle,__last), and puts the result in [__first,__last). The
2541	* output will be sorted. The sort is @e stable, that is, for
2542	* equivalent elements in the two ranges, elements from the first
2543	* range will always come before elements from the second.
2544	*
2545	* If enough additional memory is available, this takes (__last-__first)-1
2546	* comparisons. Otherwise an NlogN algorithm is used, where N is
2547	* distance(__first,__last).
2548	*/
2549	template<typename _BidirectionalIterator>
2550	_GLIBCXX26_CONSTEXPR
2551	inline void
2552	inplace_merge(_BidirectionalIterator __first,
2553	_BidirectionalIterator __middle,
2554	_BidirectionalIterator __last)
2555	{
2556	// concept requirements
2557	__glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<
2558	_BidirectionalIterator>)
2559	__glibcxx_function_requires(_LessThanComparableConcept<
2560	typename iterator_traits<_BidirectionalIterator>::value_type>)
2561	__glibcxx_requires_sorted(__first, __middle);
2562	__glibcxx_requires_sorted(__middle, __last);
2563	__glibcxx_requires_irreflexive(__first, __last);
2564
2565	std::__inplace_merge(__first, __middle, __last,
2566	__gnu_cxx::__ops::__iter_less_iter());
2567	}
2568
2569	/**
2570	* @brief Merges two sorted ranges in place.
2571	* @ingroup sorting_algorithms
2572	* @param __first An iterator.
2573	* @param __middle Another iterator.
2574	* @param __last Another iterator.
2575	* @param __comp A functor to use for comparisons.
2576	* @return Nothing.
2577	*
2578	* Merges two sorted and consecutive ranges, [__first,__middle) and
2579	* [middle,last), and puts the result in [__first,__last). The output will
2580	* be sorted. The sort is @e stable, that is, for equivalent
2581	* elements in the two ranges, elements from the first range will always
2582	* come before elements from the second.
2583	*
2584	* If enough additional memory is available, this takes (__last-__first)-1
2585	* comparisons. Otherwise an NlogN algorithm is used, where N is
2586	* distance(__first,__last).
2587	*
2588	* The comparison function should have the same effects on ordering as
2589	* the function used for the initial sort.
2590	*/
2591	template<typename _BidirectionalIterator, typename _Compare>
2592	_GLIBCXX26_CONSTEXPR
2593	inline void
2594	inplace_merge(_BidirectionalIterator __first,
2595	_BidirectionalIterator __middle,
2596	_BidirectionalIterator __last,
2597	_Compare __comp)
2598	{
2599	// concept requirements
2600	__glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<
2601	_BidirectionalIterator>)
2602	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2603	typename iterator_traits<_BidirectionalIterator>::value_type,
2604	typename iterator_traits<_BidirectionalIterator>::value_type>)
2605	__glibcxx_requires_sorted_pred(__first, __middle, __comp);
2606	__glibcxx_requires_sorted_pred(__middle, __last, __comp);
2607	__glibcxx_requires_irreflexive_pred(__first, __last, __comp);
2608
2609	std::__inplace_merge(__first, __middle, __last,
2610	__gnu_cxx::__ops::__iter_comp_iter(__comp));
2611	}
2612
2613
2614	/// This is a helper function for the __merge_sort_loop routines.
2615	template<typename _InputIterator, typename _OutputIterator,
2616	typename _Compare>
2617	_OutputIterator
2618	__move_merge(_InputIterator __first1, _InputIterator __last1,
2619	_InputIterator __first2, _InputIterator __last2,
2620	_OutputIterator __result, _Compare __comp)
2621	{
2622	while (__first1 != __last1 && __first2 != __last2)
2623	{
2624	if (__comp(__first2, __first1))
2625	{
2626	__result = _GLIBCXX_MOVE(__first2);
2627	++__first2;
2628	}
2629	else
2630	{
2631	__result = _GLIBCXX_MOVE(__first1);
2632	++__first1;
2633	}
2634	++__result;
2635	}
2636	return _GLIBCXX_MOVE3(__first2, __last2,
2637	_GLIBCXX_MOVE3(__first1, __last1,
2638	__result));
2639	}
2640
2641	template<typename _RandomAccessIterator1, typename _RandomAccessIterator2,
2642	typename _Distance, typename _Compare>
2643	void
2644	__merge_sort_loop(_RandomAccessIterator1 __first,
2645	_RandomAccessIterator1 __last,
2646	_RandomAccessIterator2 __result, _Distance __step_size,
2647	_Compare __comp)
2648	{
2649	const _Distance __two_step = `2` * __step_size;
2650
2651	while (__last - __first >= __two_step)
2652	{
2653	__result = std::__move_merge(__first, __first + __step_size,
2654	__first + __step_size,
2655	__first + __two_step,
2656	__result, __comp);
2657	__first += __two_step;
2658	}
2659	__step_size = std::min(_Distance(__last - __first), __step_size);
2660
2661	std::__move_merge(__first, __first + __step_size,
2662	__first + __step_size, __last, __result, __comp);
2663	}
2664
2665	template<typename _RandomAccessIterator, typename _Distance,
2666	typename _Compare>
2667	_GLIBCXX20_CONSTEXPR
2668	void
2669	__chunk_insertion_sort(_RandomAccessIterator __first,
2670	_RandomAccessIterator __last,
2671	_Distance __chunk_size, _Compare __comp)
2672	{
2673	while (__last - __first >= __chunk_size)
2674	{
2675	std::__insertion_sort(__first, __first + __chunk_size, __comp);
2676	__first += __chunk_size;
2677	}
2678	std::__insertion_sort(__first, __last, __comp);
2679	}
2680
2681	enum { _S_chunk_size = `7` };
2682
2683	template<typename _RandomAccessIterator, typename _Pointer, typename _Compare>
2684	void
2685	__merge_sort_with_buffer(_RandomAccessIterator __first,
2686	_RandomAccessIterator __last,
2687	_Pointer __buffer, _Compare __comp)
2688	{
2689	typedef typename iterator_traits<_RandomAccessIterator>::difference_type
2690	_Distance;
2691
2692	const _Distance __len = __last - __first;
2693	const _Pointer __buffer_last = __buffer + __len;
2694
2695	_Distance __step_size = _S_chunk_size;
2696	std::__chunk_insertion_sort(__first, __last, __step_size, __comp);
2697
2698	while (__step_size < __len)
2699	{
2700	std::__merge_sort_loop(__first, __last, __buffer,
2701	__step_size, __comp);
2702	__step_size *= `2`;
2703	std::__merge_sort_loop(__buffer, __buffer_last, __first,
2704	__step_size, __comp);
2705	__step_size *= `2`;
2706	}
2707	}
2708
2709	template<typename _RandomAccessIterator, typename _Pointer, typename _Compare>
2710	void
2711	__stable_sort_adaptive(_RandomAccessIterator __first,
2712	_RandomAccessIterator __middle,
2713	_RandomAccessIterator __last,
2714	_Pointer __buffer, _Compare __comp)
2715	{
2716	std::__merge_sort_with_buffer(__first, __middle, __buffer, __comp);
2717	std::__merge_sort_with_buffer(__middle, __last, __buffer, __comp);
2718
2719	std::__merge_adaptive(__first, __middle, __last,
2720	__middle - __first, __last - __middle,
2721	__buffer, __comp);
2722	}
2723
2724	template<typename _RandomAccessIterator, typename _Pointer,
2725	typename _Distance, typename _Compare>
2726	void
2727	__stable_sort_adaptive_resize(_RandomAccessIterator __first,
2728	_RandomAccessIterator __last,
2729	_Pointer __buffer, _Distance __buffer_size,
2730	_Compare __comp)
2731	{
2732	const _Distance __len = (__last - __first + `1`) / `2`;
2733	const _RandomAccessIterator __middle = __first + __len;
2734	if (__len > __buffer_size)
2735	{
2736	std::__stable_sort_adaptive_resize(__first, __middle, __buffer,
2737	__buffer_size, __comp);
2738	std::__stable_sort_adaptive_resize(__middle, __last, __buffer,
2739	__buffer_size, __comp);
2740	std::__merge_adaptive_resize(__first, __middle, __last,
2741	_Distance(__middle - __first),
2742	_Distance(__last - __middle),
2743	__buffer, __buffer_size,
2744	__comp);
2745	}
2746	else
2747	std::__stable_sort_adaptive(__first, __middle, __last,
2748	__buffer, __comp);
2749	}
2750
2751	/// This is a helper function for the stable sorting routines.
2752	template<typename _RandomAccessIterator, typename _Compare>
2753	_GLIBCXX26_CONSTEXPR
2754	void
2755	__inplace_stable_sort(_RandomAccessIterator __first,
2756	_RandomAccessIterator __last, _Compare __comp)
2757	{
2758	if (__last - __first < `15`)
2759	{
2760	std::__insertion_sort(__first, __last, __comp);
2761	return;
2762	}
2763	_RandomAccessIterator __middle = __first + (__last - __first) / `2`;
2764	std::__inplace_stable_sort(__first, __middle, __comp);
2765	std::__inplace_stable_sort(__middle, __last, __comp);
2766	std::__merge_without_buffer(__first, __middle, __last,
2767	__middle - __first,
2768	__last - __middle,
2769	__comp);
2770	}
2771
2772	// stable_sort
2773
2774	// Set algorithms: includes, set_union, set_intersection, set_difference,
2775	// set_symmetric_difference. All of these algorithms have the precondition
2776	// that their input ranges are sorted and the postcondition that their output
2777	// ranges are sorted.
2778
2779	template<typename _InputIterator1, typename _InputIterator2,
2780	typename _Compare>
2781	_GLIBCXX20_CONSTEXPR
2782	bool
2783	__includes(_InputIterator1 __first1, _InputIterator1 __last1,
2784	_InputIterator2 __first2, _InputIterator2 __last2,
2785	_Compare __comp)
2786	{
2787	while (__first1 != __last1 && __first2 != __last2)
2788	{
2789	if (__comp(__first2, __first1))
2790	return false;
2791	if (!__comp(__first1, __first2))
2792	++__first2;
2793	++__first1;
2794	}
2795
2796	return __first2 == __last2;
2797	}
2798
2799	/**
2800	* @brief Determines whether all elements of a sequence exists in a range.
2801	* @param __first1 Start of search range.
2802	* @param __last1 End of search range.
2803	* @param __first2 Start of sequence
2804	* @param __last2 End of sequence.
2805	* @return True if each element in [__first2,__last2) is contained in order
2806	* within [__first1,__last1). False otherwise.
2807	* @ingroup set_algorithms
2808	*
2809	* This operation expects both [__first1,__last1) and
2810	* [__first2,__last2) to be sorted. Searches for the presence of
2811	* each element in [__first2,__last2) within [__first1,__last1).
2812	* The iterators over each range only move forward, so this is a
2813	* linear algorithm. If an element in [__first2,__last2) is not
2814	* found before the search iterator reaches @p __last2, false is
2815	* returned.
2816	*/
2817	template<typename _InputIterator1, typename _InputIterator2>
2818	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
2819	inline bool
2820	includes(_InputIterator1 __first1, _InputIterator1 __last1,
2821	_InputIterator2 __first2, _InputIterator2 __last2)
2822	{
2823	// concept requirements
2824	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
2825	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
2826	__glibcxx_function_requires(_LessThanOpConcept<
2827	typename iterator_traits<_InputIterator1>::value_type,
2828	typename iterator_traits<_InputIterator2>::value_type>)
2829	__glibcxx_function_requires(_LessThanOpConcept<
2830	typename iterator_traits<_InputIterator2>::value_type,
2831	typename iterator_traits<_InputIterator1>::value_type>)
2832	__glibcxx_requires_sorted_set(__first1, __last1, __first2);
2833	__glibcxx_requires_sorted_set(__first2, __last2, __first1);
2834	__glibcxx_requires_irreflexive2(__first1, __last1);
2835	__glibcxx_requires_irreflexive2(__first2, __last2);
2836
2837	return std::__includes(__first1, __last1, __first2, __last2,
2838	__gnu_cxx::__ops::__iter_less_iter());
2839	}
2840
2841	/**
2842	* @brief Determines whether all elements of a sequence exists in a range
2843	* using comparison.
2844	* @ingroup set_algorithms
2845	* @param __first1 Start of search range.
2846	* @param __last1 End of search range.
2847	* @param __first2 Start of sequence
2848	* @param __last2 End of sequence.
2849	* @param __comp Comparison function to use.
2850	* @return True if each element in [__first2,__last2) is contained
2851	* in order within [__first1,__last1) according to comp. False
2852	* otherwise. @ingroup set_algorithms
2853	*
2854	* This operation expects both [__first1,__last1) and
2855	* [__first2,__last2) to be sorted. Searches for the presence of
2856	* each element in [__first2,__last2) within [__first1,__last1),
2857	* using comp to decide. The iterators over each range only move
2858	* forward, so this is a linear algorithm. If an element in
2859	* [__first2,__last2) is not found before the search iterator
2860	* reaches @p __last2, false is returned.
2861	*/
2862	template<typename _InputIterator1, typename _InputIterator2,
2863	typename _Compare>
2864	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
2865	inline bool
2866	includes(_InputIterator1 __first1, _InputIterator1 __last1,
2867	_InputIterator2 __first2, _InputIterator2 __last2,
2868	_Compare __comp)
2869	{
2870	// concept requirements
2871	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
2872	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
2873	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2874	typename iterator_traits<_InputIterator1>::value_type,
2875	typename iterator_traits<_InputIterator2>::value_type>)
2876	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2877	typename iterator_traits<_InputIterator2>::value_type,
2878	typename iterator_traits<_InputIterator1>::value_type>)
2879	__glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
2880	__glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);
2881	__glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
2882	__glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);
2883
2884	return std::__includes(__first1, __last1, __first2, __last2,
2885	__gnu_cxx::__ops::__iter_comp_iter(__comp));
2886	}
2887
2888	// nth_element
2889	// merge
2890	// set_difference
2891	// set_intersection
2892	// set_union
2893	// stable_sort
2894	// set_symmetric_difference
2895	// min_element
2896	// max_element
2897
2898	template<typename _BidirectionalIterator, typename _Compare>
2899	_GLIBCXX20_CONSTEXPR
2900	bool
2901	__next_permutation(_BidirectionalIterator __first,
2902	_BidirectionalIterator __last, _Compare __comp)
2903	{
2904	if (__first == __last)
2905	return false;
2906	_BidirectionalIterator __i = __first;
2907	++__i;
2908	if (__i == __last)
2909	return false;
2910	__i = __last;
2911	--__i;
2912
2913	for(;;)
2914	{
2915	_BidirectionalIterator __ii = __i;
2916	--__i;
2917	if (__comp(__i, __ii))
2918	{
2919	_BidirectionalIterator __j = __last;
2920	while (!__comp(__i, --__j))
2921	{}
2922	std::iter_swap(__i, __j);
2923	std::__reverse(__ii, __last,
2924	std::__iterator_category(__first));
2925	return true;
2926	}
2927	if (__i == __first)
2928	{
2929	std::__reverse(__first, __last,
2930	std::__iterator_category(__first));
2931	return false;
2932	}
2933	}
2934	}
2935
2936	/**
2937	* @brief Permute range into the next @e dictionary ordering.
2938	* @ingroup sorting_algorithms
2939	* @param __first Start of range.
2940	* @param __last End of range.
2941	* @return False if wrapped to first permutation, true otherwise.
2942	*
2943	* Treats all permutations of the range as a set of @e dictionary sorted
2944	* sequences. Permutes the current sequence into the next one of this set.
2945	* Returns true if there are more sequences to generate. If the sequence
2946	* is the largest of the set, the smallest is generated and false returned.
2947	*/
2948	template<typename _BidirectionalIterator>
2949	_GLIBCXX20_CONSTEXPR
2950	inline bool
2951	next_permutation(_BidirectionalIterator __first,
2952	_BidirectionalIterator __last)
2953	{
2954	// concept requirements
2955	__glibcxx_function_requires(_BidirectionalIteratorConcept<
2956	_BidirectionalIterator>)
2957	__glibcxx_function_requires(_LessThanComparableConcept<
2958	typename iterator_traits<_BidirectionalIterator>::value_type>)
2959	__glibcxx_requires_valid_range(__first, __last);
2960	__glibcxx_requires_irreflexive(__first, __last);
2961
2962	return std::__next_permutation
2963	(__first, __last, __gnu_cxx::__ops::__iter_less_iter());
2964	}
2965
2966	/**
2967	* @brief Permute range into the next @e dictionary ordering using
2968	* comparison functor.
2969	* @ingroup sorting_algorithms
2970	* @param __first Start of range.
2971	* @param __last End of range.
2972	* @param __comp A comparison functor.
2973	* @return False if wrapped to first permutation, true otherwise.
2974	*
2975	* Treats all permutations of the range [__first,__last) as a set of
2976	* @e dictionary sorted sequences ordered by @p __comp. Permutes the current
2977	* sequence into the next one of this set. Returns true if there are more
2978	* sequences to generate. If the sequence is the largest of the set, the
2979	* smallest is generated and false returned.
2980	*/
2981	template<typename _BidirectionalIterator, typename _Compare>
2982	_GLIBCXX20_CONSTEXPR
2983	inline bool
2984	next_permutation(_BidirectionalIterator __first,
2985	_BidirectionalIterator __last, _Compare __comp)
2986	{
2987	// concept requirements
2988	__glibcxx_function_requires(_BidirectionalIteratorConcept<
2989	_BidirectionalIterator>)
2990	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2991	typename iterator_traits<_BidirectionalIterator>::value_type,
2992	typename iterator_traits<_BidirectionalIterator>::value_type>)
2993	__glibcxx_requires_valid_range(__first, __last);
2994	__glibcxx_requires_irreflexive_pred(__first, __last, __comp);
2995
2996	return std::__next_permutation
2997	(__first, __last, __gnu_cxx::__ops::__iter_comp_iter(__comp));
2998	}
2999
3000	template<typename _BidirectionalIterator, typename _Compare>
3001	_GLIBCXX20_CONSTEXPR
3002	bool
3003	__prev_permutation(_BidirectionalIterator __first,
3004	_BidirectionalIterator __last, _Compare __comp)
3005	{
3006	if (__first == __last)
3007	return false;
3008	_BidirectionalIterator __i = __first;
3009	++__i;
3010	if (__i == __last)
3011	return false;
3012	__i = __last;
3013	--__i;
3014
3015	for(;;)
3016	{
3017	_BidirectionalIterator __ii = __i;
3018	--__i;
3019	if (__comp(__ii, __i))
3020	{
3021	_BidirectionalIterator __j = __last;
3022	while (!__comp(--__j, __i))
3023	{}
3024	std::iter_swap(__i, __j);
3025	std::__reverse(__ii, __last,
3026	std::__iterator_category(__first));
3027	return true;
3028	}
3029	if (__i == __first)
3030	{
3031	std::__reverse(__first, __last,
3032	std::__iterator_category(__first));
3033	return false;
3034	}
3035	}
3036	}
3037
3038	/**
3039	* @brief Permute range into the previous @e dictionary ordering.
3040	* @ingroup sorting_algorithms
3041	* @param __first Start of range.
3042	* @param __last End of range.
3043	* @return False if wrapped to last permutation, true otherwise.
3044	*
3045	* Treats all permutations of the range as a set of @e dictionary sorted
3046	* sequences. Permutes the current sequence into the previous one of this
3047	* set. Returns true if there are more sequences to generate. If the
3048	* sequence is the smallest of the set, the largest is generated and false
3049	* returned.
3050	*/
3051	template<typename _BidirectionalIterator>
3052	_GLIBCXX20_CONSTEXPR
3053	inline bool
3054	prev_permutation(_BidirectionalIterator __first,
3055	_BidirectionalIterator __last)
3056	{
3057	// concept requirements
3058	__glibcxx_function_requires(_BidirectionalIteratorConcept<
3059	_BidirectionalIterator>)
3060	__glibcxx_function_requires(_LessThanComparableConcept<
3061	typename iterator_traits<_BidirectionalIterator>::value_type>)
3062	__glibcxx_requires_valid_range(__first, __last);
3063	__glibcxx_requires_irreflexive(__first, __last);
3064
3065	return std::__prev_permutation(__first, __last,
3066	__gnu_cxx::__ops::__iter_less_iter());
3067	}
3068
3069	/**
3070	* @brief Permute range into the previous @e dictionary ordering using
3071	* comparison functor.
3072	* @ingroup sorting_algorithms
3073	* @param __first Start of range.
3074	* @param __last End of range.
3075	* @param __comp A comparison functor.
3076	* @return False if wrapped to last permutation, true otherwise.
3077	*
3078	* Treats all permutations of the range [__first,__last) as a set of
3079	* @e dictionary sorted sequences ordered by @p __comp. Permutes the current
3080	* sequence into the previous one of this set. Returns true if there are
3081	* more sequences to generate. If the sequence is the smallest of the set,
3082	* the largest is generated and false returned.
3083	*/
3084	template<typename _BidirectionalIterator, typename _Compare>
3085	_GLIBCXX20_CONSTEXPR
3086	inline bool
3087	prev_permutation(_BidirectionalIterator __first,
3088	_BidirectionalIterator __last, _Compare __comp)
3089	{
3090	// concept requirements
3091	__glibcxx_function_requires(_BidirectionalIteratorConcept<
3092	_BidirectionalIterator>)
3093	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
3094	typename iterator_traits<_BidirectionalIterator>::value_type,
3095	typename iterator_traits<_BidirectionalIterator>::value_type>)
3096	__glibcxx_requires_valid_range(__first, __last);
3097	__glibcxx_requires_irreflexive_pred(__first, __last, __comp);
3098
3099	return std::__prev_permutation(__first, __last,
3100	__gnu_cxx::__ops::__iter_comp_iter(__comp));
3101	}
3102
3103	// replace
3104	// replace_if
3105
3106	template<typename _InputIterator, typename _OutputIterator,
3107	typename _Predicate, typename _Tp>
3108	_GLIBCXX20_CONSTEXPR
3109	_OutputIterator
3110	__replace_copy_if(_InputIterator __first, _InputIterator __last,
3111	_OutputIterator __result,
3112	_Predicate __pred, const _Tp& __new_value)
3113	{
3114	for (; __first != __last; ++__first, (void)++__result)
3115	if (__pred(__first))
3116	*__result = __new_value;
3117	else
3118	__result = __first;
3119	return __result;
3120	}
3121
3122	/**
3123	* @brief Copy a sequence, replacing each element of one value with another
3124	* value.
3125	* @param __first An input iterator.
3126	* @param __last An input iterator.
3127	* @param __result An output iterator.
3128	* @param __old_value The value to be replaced.
3129	* @param __new_value The replacement value.
3130	* @return The end of the output sequence, @p result+(last-first).
3131	*
3132	* Copies each element in the input range @p [__first,__last) to the
3133	* output range @p [__result,__result+(__last-__first)) replacing elements
3134	* equal to @p __old_value with @p __new_value.
3135	*/
3136	template<typename _InputIterator, typename _OutputIterator, typename _Tp>
3137	_GLIBCXX20_CONSTEXPR
3138	inline _OutputIterator
3139	replace_copy(_InputIterator __first, _InputIterator __last,
3140	_OutputIterator __result,
3141	const _Tp& __old_value, const _Tp& __new_value)
3142	{
3143	// concept requirements
3144	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3145	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
3146	typename iterator_traits<_InputIterator>::value_type>)
3147	__glibcxx_function_requires(_EqualOpConcept<
3148	typename iterator_traits<_InputIterator>::value_type, _Tp>)
3149	__glibcxx_requires_valid_range(__first, __last);
3150
3151	return std::__replace_copy_if(__first, __last, __result,
3152	__gnu_cxx::__ops::__iter_equals_val(__old_value),
3153	__new_value);
3154	}
3155
3156	/**
3157	* @brief Copy a sequence, replacing each value for which a predicate
3158	* returns true with another value.
3159	* @ingroup mutating_algorithms
3160	* @param __first An input iterator.
3161	* @param __last An input iterator.
3162	* @param __result An output iterator.
3163	* @param __pred A predicate.
3164	* @param __new_value The replacement value.
3165	* @return The end of the output sequence, @p __result+(__last-__first).
3166	*
3167	* Copies each element in the range @p [__first,__last) to the range
3168	* @p [__result,__result+(__last-__first)) replacing elements for which
3169	* @p __pred returns true with @p __new_value.
3170	*/
3171	template<typename _InputIterator, typename _OutputIterator,
3172	typename _Predicate, typename _Tp>
3173	_GLIBCXX20_CONSTEXPR
3174	inline _OutputIterator
3175	replace_copy_if(_InputIterator __first, _InputIterator __last,
3176	_OutputIterator __result,
3177	_Predicate __pred, const _Tp& __new_value)
3178	{
3179	// concept requirements
3180	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3181	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
3182	typename iterator_traits<_InputIterator>::value_type>)
3183	__glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
3184	typename iterator_traits<_InputIterator>::value_type>)
3185	__glibcxx_requires_valid_range(__first, __last);
3186
3187	return std::__replace_copy_if(__first, __last, __result,
3188	__gnu_cxx::__ops::__pred_iter(__pred),
3189	__new_value);
3190	}
3191
3192	#if __cplusplus >= 201103L
3193	/**
3194	* @brief Determines whether the elements of a sequence are sorted.
3195	* @ingroup sorting_algorithms
3196	* @param __first An iterator.
3197	* @param __last Another iterator.
3198	* @return True if the elements are sorted, false otherwise.
3199	*/
3200	template<typename _ForwardIterator>
3201	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
3202	inline bool
3203	is_sorted(_ForwardIterator __first, _ForwardIterator __last)
3204	{ return std::is_sorted_until(__first, __last) == __last; }
3205
3206	/**
3207	* @brief Determines whether the elements of a sequence are sorted
3208	* according to a comparison functor.
3209	* @ingroup sorting_algorithms
3210	* @param __first An iterator.
3211	* @param __last Another iterator.
3212	* @param __comp A comparison functor.
3213	* @return True if the elements are sorted, false otherwise.
3214	*/
3215	template<typename _ForwardIterator, typename _Compare>
3216	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
3217	inline bool
3218	is_sorted(_ForwardIterator __first, _ForwardIterator __last,
3219	_Compare __comp)
3220	{ return std::is_sorted_until(__first, __last, __comp) == __last; }
3221
3222	template<typename _ForwardIterator, typename _Compare>
3223	_GLIBCXX20_CONSTEXPR
3224	_ForwardIterator
3225	__is_sorted_until(_ForwardIterator __first, _ForwardIterator __last,
3226	_Compare __comp)
3227	{
3228	if (__first == __last)
3229	return __last;
3230
3231	_ForwardIterator __next = __first;
3232	for (++__next; __next != __last; __first = __next, (void)++__next)
3233	if (__comp(__next, __first))
3234	return __next;
3235	return __next;
3236	}
3237
3238	/**
3239	* @brief Determines the end of a sorted sequence.
3240	* @ingroup sorting_algorithms
3241	* @param __first An iterator.
3242	* @param __last Another iterator.
3243	* @return An iterator pointing to the last iterator i in [__first, __last)
3244	* for which the range [__first, i) is sorted.
3245	*/
3246	template<typename _ForwardIterator>
3247	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
3248	inline _ForwardIterator
3249	is_sorted_until(_ForwardIterator __first, _ForwardIterator __last)
3250	{
3251	// concept requirements
3252	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
3253	__glibcxx_function_requires(_LessThanComparableConcept<
3254	typename iterator_traits<_ForwardIterator>::value_type>)
3255	__glibcxx_requires_valid_range(__first, __last);
3256	__glibcxx_requires_irreflexive(__first, __last);
3257
3258	return std::__is_sorted_until(__first, __last,
3259	__gnu_cxx::__ops::__iter_less_iter());
3260	}
3261
3262	/**
3263	* @brief Determines the end of a sorted sequence using comparison functor.
3264	* @ingroup sorting_algorithms
3265	* @param __first An iterator.
3266	* @param __last Another iterator.
3267	* @param __comp A comparison functor.
3268	* @return An iterator pointing to the last iterator i in [__first, __last)
3269	* for which the range [__first, i) is sorted.
3270	*/
3271	template<typename _ForwardIterator, typename _Compare>
3272	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
3273	inline _ForwardIterator
3274	is_sorted_until(_ForwardIterator __first, _ForwardIterator __last,
3275	_Compare __comp)
3276	{
3277	// concept requirements
3278	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
3279	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
3280	typename iterator_traits<_ForwardIterator>::value_type,
3281	typename iterator_traits<_ForwardIterator>::value_type>)
3282	__glibcxx_requires_valid_range(__first, __last);
3283	__glibcxx_requires_irreflexive_pred(__first, __last, __comp);
3284
3285	return std::__is_sorted_until(__first, __last,
3286	__gnu_cxx::__ops::__iter_comp_iter(__comp));
3287	}
3288
3289	/**
3290	* @brief Determines min and max at once as an ordered pair.
3291	* @ingroup sorting_algorithms
3292	* @param __a A thing of arbitrary type.
3293	* @param __b Another thing of arbitrary type.
3294	* @return A pair(__b, __a) if __b is smaller than __a, pair(__a,
3295	* __b) otherwise.
3296	*/
3297	template<typename _Tp>
3298	_GLIBCXX_NODISCARD _GLIBCXX14_CONSTEXPR
3299	inline pair<const _Tp&, const _Tp&>
3300	minmax(const _Tp& __a, const _Tp& __b)
3301	{
3302	// concept requirements
3303	__glibcxx_function_requires(_LessThanComparableConcept<_Tp>)
3304
3305	return __b < __a ? pair<const _Tp&, const _Tp&>(__b, __a)
3306	: pair<const _Tp&, const _Tp&>(__a, __b);
3307	}
3308
3309	/**
3310	* @brief Determines min and max at once as an ordered pair.
3311	* @ingroup sorting_algorithms
3312	* @param __a A thing of arbitrary type.
3313	* @param __b Another thing of arbitrary type.
3314	* @param __comp A @link comparison_functors comparison functor @endlink.
3315	* @return A pair(__b, __a) if __b is smaller than __a, pair(__a,
3316	* __b) otherwise.
3317	*/
3318	template<typename _Tp, typename _Compare>
3319	_GLIBCXX_NODISCARD _GLIBCXX14_CONSTEXPR
3320	inline pair<const _Tp&, const _Tp&>
3321	minmax(const _Tp& __a, const _Tp& __b, _Compare __comp)
3322	{
3323	return __comp(__b, __a) ? pair<const _Tp&, const _Tp&>(__b, __a)
3324	: pair<const _Tp&, const _Tp&>(__a, __b);
3325	}
3326
3327	template<typename _ForwardIterator, typename _Compare>
3328	_GLIBCXX14_CONSTEXPR
3329	pair<_ForwardIterator, _ForwardIterator>
3330	__minmax_element(_ForwardIterator __first, _ForwardIterator __last,
3331	_Compare __comp)
3332	{
3333	_ForwardIterator __next = __first;
3334	if (__first == __last
3335	\|\| ++__next == __last)
3336	return std::make_pair(__first, __first);
3337
3338	_ForwardIterator __min{}, __max{};
3339	if (__comp(__next, __first))
3340	{
3341	__min = __next;
3342	__max = __first;
3343	}
3344	else
3345	{
3346	__min = __first;
3347	__max = __next;
3348	}
3349
3350	__first = __next;
3351	++__first;
3352
3353	while (__first != __last)
3354	{
3355	__next = __first;
3356	if (++__next == __last)
3357	{
3358	if (__comp(__first, __min))
3359	__min = __first;
3360	else if (!__comp(__first, __max))
3361	__max = __first;
3362	break;
3363	}
3364
3365	if (__comp(__next, __first))
3366	{
3367	if (__comp(__next, __min))
3368	__min = __next;
3369	if (!__comp(__first, __max))
3370	__max = __first;
3371	}
3372	else
3373	{
3374	if (__comp(__first, __min))
3375	__min = __first;
3376	if (!__comp(__next, __max))
3377	__max = __next;
3378	}
3379
3380	__first = __next;
3381	++__first;
3382	}
3383
3384	return std::make_pair(__min, __max);
3385	}
3386
3387	/**
3388	* @brief Return a pair of iterators pointing to the minimum and maximum
3389	* elements in a range.
3390	* @ingroup sorting_algorithms
3391	* @param __first Start of range.
3392	* @param __last End of range.
3393	* @return make_pair(m, M), where m is the first iterator i in
3394	* [__first, __last) such that no other element in the range is
3395	* smaller, and where M is the last iterator i in [__first, __last)
3396	* such that no other element in the range is larger.
3397	*/
3398	template<typename _ForwardIterator>
3399	_GLIBCXX_NODISCARD _GLIBCXX14_CONSTEXPR
3400	inline pair<_ForwardIterator, _ForwardIterator>
3401	minmax_element(_ForwardIterator __first, _ForwardIterator __last)
3402	{
3403	// concept requirements
3404	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
3405	__glibcxx_function_requires(_LessThanComparableConcept<
3406	typename iterator_traits<_ForwardIterator>::value_type>)
3407	__glibcxx_requires_valid_range(__first, __last);
3408	__glibcxx_requires_irreflexive(__first, __last);
3409
3410	return std::__minmax_element(__first, __last,
3411	__gnu_cxx::__ops::__iter_less_iter());
3412	}
3413
3414	/**
3415	* @brief Return a pair of iterators pointing to the minimum and maximum
3416	* elements in a range.
3417	* @ingroup sorting_algorithms
3418	* @param __first Start of range.
3419	* @param __last End of range.
3420	* @param __comp Comparison functor.
3421	* @return make_pair(m, M), where m is the first iterator i in
3422	* [__first, __last) such that no other element in the range is
3423	* smaller, and where M is the last iterator i in [__first, __last)
3424	* such that no other element in the range is larger.
3425	*/
3426	template<typename _ForwardIterator, typename _Compare>
3427	_GLIBCXX_NODISCARD _GLIBCXX14_CONSTEXPR
3428	inline pair<_ForwardIterator, _ForwardIterator>
3429	minmax_element(_ForwardIterator __first, _ForwardIterator __last,
3430	_Compare __comp)
3431	{
3432	// concept requirements
3433	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
3434	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
3435	typename iterator_traits<_ForwardIterator>::value_type,
3436	typename iterator_traits<_ForwardIterator>::value_type>)
3437	__glibcxx_requires_valid_range(__first, __last);
3438	__glibcxx_requires_irreflexive_pred(__first, __last, __comp);
3439
3440	return std::__minmax_element(__first, __last,
3441	__gnu_cxx::__ops::__iter_comp_iter(__comp));
3442	}
3443
3444	template<typename _Tp>
3445	_GLIBCXX_NODISCARD _GLIBCXX14_CONSTEXPR
3446	inline pair<_Tp, _Tp>
3447	minmax(initializer_list<_Tp> __l)
3448	{
3449	__glibcxx_requires_irreflexive(__l.begin(), __l.end());
3450	pair<const _Tp, const* _Tp*> __p =
3451	std::__minmax_element(__l.begin(), __l.end(),
3452	__gnu_cxx::__ops::__iter_less_iter());
3453	return std::make_pair(__p.first, __p.second);
3454	}
3455
3456	template<typename _Tp, typename _Compare>
3457	_GLIBCXX_NODISCARD _GLIBCXX14_CONSTEXPR
3458	inline pair<_Tp, _Tp>
3459	minmax(initializer_list<_Tp> __l, _Compare __comp)
3460	{
3461	__glibcxx_requires_irreflexive_pred(__l.begin(), __l.end(), __comp);
3462	pair<const _Tp, const* _Tp*> __p =
3463	std::__minmax_element(__l.begin(), __l.end(),
3464	__gnu_cxx::__ops::__iter_comp_iter(__comp));
3465	return std::make_pair(__p.first, __p.second);
3466	}
3467
3468	/**
3469	* @brief Checks whether a permutation of the second sequence is equal
3470	* to the first sequence.
3471	* @ingroup non_mutating_algorithms
3472	* @param __first1 Start of first range.
3473	* @param __last1 End of first range.
3474	* @param __first2 Start of second range.
3475	* @param __pred A binary predicate.
3476	* @return true if there exists a permutation of the elements in
3477	* the range [__first2, __first2 + (__last1 - __first1)),
3478	* beginning with ForwardIterator2 begin, such that
3479	* equal(__first1, __last1, __begin, __pred) returns true;
3480	* otherwise, returns false.
3481	*/
3482	template<typename _ForwardIterator1, typename _ForwardIterator2,
3483	typename _BinaryPredicate>
3484	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
3485	inline bool
3486	is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
3487	_ForwardIterator2 __first2, _BinaryPredicate __pred)
3488	{
3489	// concept requirements
3490	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
3491	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
3492	__glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
3493	typename iterator_traits<_ForwardIterator1>::value_type,
3494	typename iterator_traits<_ForwardIterator2>::value_type>)
3495	__glibcxx_requires_valid_range(__first1, __last1);
3496
3497	return std::__is_permutation(__first1, __last1, __first2,
3498	__gnu_cxx::__ops::__iter_comp_iter(__pred));
3499	}
3500
3501	#if __cplusplus > 201103L
3502	#pragma GCC diagnostic push
3503	#pragma GCC diagnostic ignored "-Wc++17-extensions" // if constexpr
3504	template<typename _ForwardIterator1, typename _ForwardIterator2,
3505	typename _BinaryPredicate>
3506	_GLIBCXX20_CONSTEXPR
3507	bool
3508	__is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
3509	_ForwardIterator2 __first2, _ForwardIterator2 __last2,
3510	_BinaryPredicate __pred)
3511	{
3512	using _Cat1
3513	= typename iterator_traits<_ForwardIterator1>::iterator_category;
3514	using _Cat2
3515	= typename iterator_traits<_ForwardIterator2>::iterator_category;
3516	using _It1_is_RA = is_same<_Cat1, random_access_iterator_tag>;
3517	using _It2_is_RA = is_same<_Cat2, random_access_iterator_tag>;
3518	constexpr bool __ra_iters = __and_<_It1_is_RA, _It2_is_RA>::value;
3519	if constexpr (__ra_iters)
3520	{
3521	if ((__last1 - __first1) != (__last2 - __first2))
3522	return false;
3523	}
3524
3525	// Efficiently compare identical prefixes: O(N) if sequences
3526	// have the same elements in the same order.
3527	for (; __first1 != __last1 && __first2 != __last2;
3528	++__first1, (void)++__first2)
3529	if (!__pred(__first1, __first2))
3530	break;
3531
3532	if constexpr (__ra_iters)
3533	{
3534	if (__first1 == __last1)
3535	return true;
3536	}
3537	else
3538	{
3539	auto __d1 = std::distance(__first1, __last1);
3540	auto __d2 = std::distance(__first2, __last2);
3541	if (__d1 == `0` && __d2 == `0`)
3542	return true;
3543	if (__d1 != __d2)
3544	return false;
3545	}
3546
3547	for (_ForwardIterator1 __scan = __first1; __scan != __last1; ++__scan)
3548	{
3549	if (__scan != std::__find_if(__first1, __scan,
3550	__gnu_cxx::__ops::__iter_comp_iter(__pred, __scan)))
3551	continue; // We've seen this one before.
3552
3553	auto __matches = std::__count_if(__first2, __last2,
3554	__gnu_cxx::__ops::__iter_comp_iter(__pred, __scan));
3555	if (`0` == __matches
3556	\|\| std::__count_if(__scan, __last1,
3557	__gnu_cxx::__ops::__iter_comp_iter(__pred, __scan))
3558	!= __matches)
3559	return false;
3560	}
3561	return true;
3562	}
3563	#pragma GCC diagnostic pop
3564
3565	/**
3566	* @brief Checks whether a permutaion of the second sequence is equal
3567	* to the first sequence.
3568	* @ingroup non_mutating_algorithms
3569	* @param __first1 Start of first range.
3570	* @param __last1 End of first range.
3571	* @param __first2 Start of second range.
3572	* @param __last2 End of first range.
3573	* @return true if there exists a permutation of the elements in the range
3574	* [__first2, __last2), beginning with ForwardIterator2 begin,
3575	* such that equal(__first1, __last1, begin) returns true;
3576	* otherwise, returns false.
3577	*/
3578	template<typename _ForwardIterator1, typename _ForwardIterator2>
3579	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
3580	inline bool
3581	is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
3582	_ForwardIterator2 __first2, _ForwardIterator2 __last2)
3583	{
3584	__glibcxx_requires_valid_range(__first1, __last1);
3585	__glibcxx_requires_valid_range(__first2, __last2);
3586
3587	return
3588	std::__is_permutation(__first1, __last1, __first2, __last2,
3589	__gnu_cxx::__ops::__iter_equal_to_iter());
3590	}
3591
3592	/**
3593	* @brief Checks whether a permutation of the second sequence is equal
3594	* to the first sequence.
3595	* @ingroup non_mutating_algorithms
3596	* @param __first1 Start of first range.
3597	* @param __last1 End of first range.
3598	* @param __first2 Start of second range.
3599	* @param __last2 End of first range.
3600	* @param __pred A binary predicate.
3601	* @return true if there exists a permutation of the elements in the range
3602	* [__first2, __last2), beginning with ForwardIterator2 begin,
3603	* such that equal(__first1, __last1, __begin, __pred) returns true;
3604	* otherwise, returns false.
3605	*/
3606	template<typename _ForwardIterator1, typename _ForwardIterator2,
3607	typename _BinaryPredicate>
3608	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
3609	inline bool
3610	is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
3611	_ForwardIterator2 __first2, _ForwardIterator2 __last2,
3612	_BinaryPredicate __pred)
3613	{
3614	__glibcxx_requires_valid_range(__first1, __last1);
3615	__glibcxx_requires_valid_range(__first2, __last2);
3616
3617	return std::__is_permutation(__first1, __last1, __first2, __last2,
3618	__gnu_cxx::__ops::__iter_comp_iter(__pred));
3619	}
3620	#endif // C++14
3621
3622	#ifdef __glibcxx_clamp // C++ >= 17
3623	/**
3624	* @brief Returns the value clamped between lo and hi.
3625	* @ingroup sorting_algorithms
3626	* @param __val A value of arbitrary type.
3627	* @param __lo A lower limit of arbitrary type.
3628	* @param __hi An upper limit of arbitrary type.
3629	* @retval `__lo` if `__val < __lo`
3630	* @retval `__hi` if `__hi < __val`
3631	* @retval `__val` otherwise.
3632	* @pre `_Tp` is LessThanComparable and `(__hi < __lo)` is false.
3633	*/
3634	template<typename _Tp>
3635	[[nodiscard]] constexpr const _Tp&
3636	clamp(const _Tp& __val, const _Tp& __lo, const _Tp& __hi)
3637	{
3638	__glibcxx_assert(!(__hi < __lo));
3639	return std::min(std::max(__val, __lo), __hi);
3640	}
3641
3642	/**
3643	* @brief Returns the value clamped between lo and hi.
3644	* @ingroup sorting_algorithms
3645	* @param __val A value of arbitrary type.
3646	* @param __lo A lower limit of arbitrary type.
3647	* @param __hi An upper limit of arbitrary type.
3648	* @param __comp A comparison functor.
3649	* @retval `__lo` if `__comp(__val, __lo)`
3650	* @retval `__hi` if `__comp(__hi, __val)`
3651	* @retval `__val` otherwise.
3652	* @pre `__comp(__hi, __lo)` is false.
3653	*/
3654	template<typename _Tp, typename _Compare>
3655	[[nodiscard]] constexpr const _Tp&
3656	clamp(const _Tp& __val, const _Tp& __lo, const _Tp& __hi, _Compare __comp)
3657	{
3658	__glibcxx_assert(!__comp(__hi, __lo));
3659	return std::min(std::max(__val, __lo, __comp), __hi, __comp);
3660	}
3661	#endif // __glibcxx_clamp
3662
3663	/**
3664	* @brief Generate two uniformly distributed integers using a
3665	* single distribution invocation.
3666	* @param __b0 The upper bound for the first integer.
3667	* @param __b1 The upper bound for the second integer.
3668	* @param __g A UniformRandomBitGenerator.
3669	* @return A pair (i, j) with i and j uniformly distributed
3670	* over [0, __b0) and [0, __b1), respectively.
3671	*
3672	* Requires: __b0 * __b1 <= __g.max() - __g.min().
3673	*
3674	* Using uniform_int_distribution with a range that is very
3675	* small relative to the range of the generator ends up wasting
3676	* potentially expensively generated randomness, since
3677	* uniform_int_distribution does not store leftover randomness
3678	* between invocations.
3679	*
3680	* If we know we want two integers in ranges that are sufficiently
3681	* small, we can compose the ranges, use a single distribution
3682	* invocation, and significantly reduce the waste.
3683	*/
3684	template<typename _IntType, typename _UniformRandomBitGenerator>
3685	pair<_IntType, _IntType>
3686	__gen_two_uniform_ints(_IntType __b0, _IntType __b1,
3687	_UniformRandomBitGenerator&& __g)
3688	{
3689	_IntType __x
3690	= uniform_int_distribution<_IntType>{`0`, (__b0 * __b1) - `1`}(__g);
3691	return std::make_pair(__x / __b1, __x % __b1);
3692	}
3693
3694	/**
3695	* @brief Shuffle the elements of a sequence using a uniform random
3696	* number generator.
3697	* @ingroup mutating_algorithms
3698	* @param __first A forward iterator.
3699	* @param __last A forward iterator.
3700	* @param __g A UniformRandomNumberGenerator (26.5.1.3).
3701	* @return Nothing.
3702	*
3703	* Reorders the elements in the range @p [__first,__last) using @p __g to
3704	* provide random numbers.
3705	*/
3706	template<typename _RandomAccessIterator,
3707	typename _UniformRandomNumberGenerator>
3708	void
3709	shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last,
3710	_UniformRandomNumberGenerator&& __g)
3711	{
3712	// concept requirements
3713	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
3714	_RandomAccessIterator>)
3715	__glibcxx_requires_valid_range(__first, __last);
3716
3717	if (__first == __last)
3718	return;
3719
3720	typedef typename iterator_traits<_RandomAccessIterator>::difference_type
3721	_DistanceType;
3722
3723	typedef typename std::make_unsigned<_DistanceType>::type __ud_type;
3724	typedef typename std::uniform_int_distribution<__ud_type> __distr_type;
3725	typedef typename __distr_type::param_type __p_type;
3726
3727	typedef typename remove_reference<_UniformRandomNumberGenerator>::type
3728	_Gen;
3729	typedef typename common_type<typename _Gen::result_type, __ud_type>::type
3730	__uc_type;
3731
3732	const __uc_type __urngrange = __g.max() - __g.min();
3733	const __uc_type __urange = __uc_type(__last - __first);
3734
3735	if (__urngrange / __urange >= __urange)
3736	// I.e. (__urngrange >= __urange __urange) but without wrap issues.*
3737	{
3738	_RandomAccessIterator __i = __first + `1`;
3739
3740	// Since we know the range isn't empty, an even number of elements
3741	// means an uneven number of elements /to swap/, in which case we
3742	// do the first one up front:
3743
3744	if ((__urange % `2`) == `0`)
3745	{
3746	__distr_type __d{`0`, `1`};
3747	std::iter_swap(__i++, __first + __d(__g));
3748	}
3749
3750	// Now we know that __last - __i is even, so we do the rest in pairs,
3751	// using a single distribution invocation to produce swap positions
3752	// for two successive elements at a time:
3753
3754	while (__i != __last)
3755	{
3756	const __uc_type __swap_range = __uc_type(__i - __first) + `1`;
3757
3758	const pair<__uc_type, __uc_type> __pospos =
3759	__gen_two_uniform_ints(__swap_range, __swap_range + `1`, __g);
3760
3761	std::iter_swap(__i++, __first + __pospos.first);
3762	std::iter_swap(__i++, __first + __pospos.second);
3763	}
3764
3765	return;
3766	}
3767
3768	__distr_type __d;
3769
3770	for (_RandomAccessIterator __i = __first + `1`; __i != __last; ++__i)
3771	std::iter_swap(__i, __first + __d(__g, __p_type(`0`, __i - __first)));
3772	}
3773	#endif // C++11
3774
3775	_GLIBCXX_BEGIN_NAMESPACE_ALGO
3776
3777	/**
3778	* @brief Apply a function to every element of a sequence.
3779	* @ingroup non_mutating_algorithms
3780	* @param __first An input iterator.
3781	* @param __last An input iterator.
3782	* @param __f A unary function object.
3783	* @return @p __f
3784	*
3785	* Applies the function object @p __f to each element in the range
3786	* @p [first,last). @p __f must not modify the order of the sequence.
3787	* If @p __f has a return value it is ignored.
3788	*/
3789	template<typename _InputIterator, typename _Function>
3790	_GLIBCXX20_CONSTEXPR
3791	_Function
3792	for_each(_InputIterator __first, _InputIterator __last, _Function __f)
3793	{
3794	// concept requirements
3795	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3796	__glibcxx_requires_valid_range(__first, __last);
3797	for (; __first != __last; ++__first)
3798	__f(*__first);
3799	return __f; // N.B. [alg.foreach] says std::move(f) but it's redundant.
3800	}
3801
3802	#if __cplusplus >= 201703L
3803	/**
3804	* @brief Apply a function to every element of a sequence.
3805	* @ingroup non_mutating_algorithms
3806	* @param __first An input iterator.
3807	* @param __n A value convertible to an integer.
3808	* @param __f A unary function object.
3809	* @return `__first+__n`
3810	*
3811	* Applies the function object `__f` to each element in the range
3812	* `[first, first+n)`. `__f` must not modify the order of the sequence.
3813	* If `__f` has a return value it is ignored.
3814	*/
3815	template<typename _InputIterator, typename _Size, typename _Function>
3816	_GLIBCXX20_CONSTEXPR
3817	_InputIterator
3818	for_each_n(_InputIterator __first, _Size __n, _Function __f)
3819	{
3820	auto __n2 = std::__size_to_integer(__n);
3821	using _Cat = typename iterator_traits<_InputIterator>::iterator_category;
3822	if constexpr (is_base_of_v<random_access_iterator_tag, _Cat>)
3823	{
3824	if (__n2 <= `0`)
3825	return __first;
3826	auto __last = __first + __n2;
3827	std::for_each(__first, __last, std::move(__f));
3828	return __last;
3829	}
3830	else
3831	{
3832	while (__n2-->`0`)
3833	{
3834	__f(*__first);
3835	++__first;
3836	}
3837	return __first;
3838	}
3839	}
3840	#endif // C++17
3841
3842	/**
3843	* @brief Find the first occurrence of a value in a sequence.
3844	* @ingroup non_mutating_algorithms
3845	* @param __first An input iterator.
3846	* @param __last An input iterator.
3847	* @param __val The value to find.
3848	* @return The first iterator @c i in the range @p [__first,__last)
3849	* such that @c *i == @p __val, or @p __last if no such iterator exists.
3850	*/
3851	template<typename _InputIterator, typename _Tp>
3852	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
3853	inline _InputIterator
3854	find(_InputIterator __first, _InputIterator __last, const _Tp& __val)
3855	{
3856	// concept requirements
3857	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3858	__glibcxx_function_requires(_EqualOpConcept<
3859	typename iterator_traits<_InputIterator>::value_type, _Tp>)
3860	__glibcxx_requires_valid_range(__first, __last);
3861
3862	#if __cpp_if_constexpr && __glibcxx_type_trait_variable_templates
3863	using _ValT = typename iterator_traits<_InputIterator>::value_type;
3864	if constexpr (__can_use_memchr_for_find<_ValT, _Tp>)
3865	if constexpr (is_pointer_v<decltype(std::__niter_base(__first))>
3866	#if __glibcxx_concepts && __glibcxx_to_address
3867	\|\| contiguous_iterator<_InputIterator>
3868	#endif
3869	)
3870	{
3871	// If conversion to the 1-byte value_type alters the value,
3872	// it would not be found by std::find using equality comparison.
3873	// We need to check this here, because otherwise something like
3874	// memchr("a", 'a'+256, 1) would give a false positive match.
3875	if (!(static_cast<_ValT>(__val) == __val))
3876	return __last;
3877	else if (!__is_constant_evaluated())
3878	{
3879	const int __ival = static_cast<int>(__val);
3880	if (auto __n = __last - __first; __n > `0`)
3881	{
3882	#if __glibcxx_concepts && __glibcxx_to_address
3883	const void* __p0 = std::to_address(__first);
3884	#else
3885	const void* __p0 = std::__niter_base(__first);
3886	#endif
3887	if (auto __p1 = __builtin_memchr(__p0, __ival, __n))
3888	return __first + ((const char)__p1 - (const* char*)__p0);
3889	}
3890	return __last;
3891	}
3892	}
3893	#endif
3894
3895	return std::__find_if(__first, __last,
3896	__gnu_cxx::__ops::__iter_equals_val(__val));
3897	}
3898
3899	/**
3900	* @brief Find the first element in a sequence for which a
3901	* predicate is true.
3902	* @ingroup non_mutating_algorithms
3903	* @param __first An input iterator.
3904	* @param __last An input iterator.
3905	* @param __pred A predicate.
3906	* @return The first iterator @c i in the range @p [__first,__last)
3907	* such that @p __pred(*i) is true, or @p __last if no such iterator exists.
3908	*/
3909	template<typename _InputIterator, typename _Predicate>
3910	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
3911	inline _InputIterator
3912	find_if(_InputIterator __first, _InputIterator __last,
3913	_Predicate __pred)
3914	{
3915	// concept requirements
3916	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3917	__glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
3918	typename iterator_traits<_InputIterator>::value_type>)
3919	__glibcxx_requires_valid_range(__first, __last);
3920
3921	return std::__find_if(__first, __last,
3922	__gnu_cxx::__ops::__pred_iter(__pred));
3923	}
3924
3925	/**
3926	* @brief Find element from a set in a sequence.
3927	* @ingroup non_mutating_algorithms
3928	* @param __first1 Start of range to search.
3929	* @param __last1 End of range to search.
3930	* @param __first2 Start of match candidates.
3931	* @param __last2 End of match candidates.
3932	* @return The first iterator @c i in the range
3933	* @p [__first1,__last1) such that @c i == @p (i2) such that i2 is an
3934	* iterator in [__first2,__last2), or @p __last1 if no such iterator exists.
3935	*
3936	* Searches the range @p [__first1,__last1) for an element that is
3937	* equal to some element in the range [__first2,__last2). If
3938	* found, returns an iterator in the range [__first1,__last1),
3939	* otherwise returns @p __last1.
3940	*/
3941	template<typename _InputIterator, typename _ForwardIterator>
3942	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
3943	_InputIterator
3944	find_first_of(_InputIterator __first1, _InputIterator __last1,
3945	_ForwardIterator __first2, _ForwardIterator __last2)
3946	{
3947	// concept requirements
3948	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3949	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
3950	__glibcxx_function_requires(_EqualOpConcept<
3951	typename iterator_traits<_InputIterator>::value_type,
3952	typename iterator_traits<_ForwardIterator>::value_type>)
3953	__glibcxx_requires_valid_range(__first1, __last1);
3954	__glibcxx_requires_valid_range(__first2, __last2);
3955
3956	for (; __first1 != __last1; ++__first1)
3957	for (_ForwardIterator __iter = __first2; __iter != __last2; ++__iter)
3958	if (__first1 == __iter)
3959	return __first1;
3960	return __last1;
3961	}
3962
3963	/**
3964	* @brief Find element from a set in a sequence using a predicate.
3965	* @ingroup non_mutating_algorithms
3966	* @param __first1 Start of range to search.
3967	* @param __last1 End of range to search.
3968	* @param __first2 Start of match candidates.
3969	* @param __last2 End of match candidates.
3970	* @param __comp Predicate to use.
3971	* @return The first iterator @c i in the range
3972	* @p [__first1,__last1) such that @c comp(i, @p (i2)) is true
3973	* and i2 is an iterator in [__first2,__last2), or @p __last1 if no
3974	* such iterator exists.
3975	*
3976
3977	* Searches the range @p [__first1,__last1) for an element that is
3978	* equal to some element in the range [__first2,__last2). If
3979	* found, returns an iterator in the range [__first1,__last1),
3980	* otherwise returns @p __last1.
3981	*/
3982	template<typename _InputIterator, typename _ForwardIterator,
3983	typename _BinaryPredicate>
3984	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
3985	_InputIterator
3986	find_first_of(_InputIterator __first1, _InputIterator __last1,
3987	_ForwardIterator __first2, _ForwardIterator __last2,
3988	_BinaryPredicate __comp)
3989	{
3990	// concept requirements
3991	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3992	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
3993	__glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
3994	typename iterator_traits<_InputIterator>::value_type,
3995	typename iterator_traits<_ForwardIterator>::value_type>)
3996	__glibcxx_requires_valid_range(__first1, __last1);
3997	__glibcxx_requires_valid_range(__first2, __last2);
3998
3999	for (; __first1 != __last1; ++__first1)
4000	for (_ForwardIterator __iter = __first2; __iter != __last2; ++__iter)
4001	if (__comp(__first1, __iter))
4002	return __first1;
4003	return __last1;
4004	}
4005
4006	/**
4007	* @brief Find two adjacent values in a sequence that are equal.
4008	* @ingroup non_mutating_algorithms
4009	* @param __first A forward iterator.
4010	* @param __last A forward iterator.
4011	* @return The first iterator @c i such that @c i and @c i+1 are both
4012	* valid iterators in @p [__first,__last) and such that @c i == @c (i+1),
4013	* or @p __last if no such iterator exists.
4014	*/
4015	template<typename _ForwardIterator>
4016	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
4017	inline _ForwardIterator
4018	adjacent_find(_ForwardIterator __first, _ForwardIterator __last)
4019	{
4020	// concept requirements
4021	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
4022	__glibcxx_function_requires(_EqualityComparableConcept<
4023	typename iterator_traits<_ForwardIterator>::value_type>)
4024	__glibcxx_requires_valid_range(__first, __last);
4025
4026	return std::__adjacent_find(__first, __last,
4027	__gnu_cxx::__ops::__iter_equal_to_iter());
4028	}
4029
4030	/**
4031	* @brief Find two adjacent values in a sequence using a predicate.
4032	* @ingroup non_mutating_algorithms
4033	* @param __first A forward iterator.
4034	* @param __last A forward iterator.
4035	* @param __binary_pred A binary predicate.
4036	* @return The first iterator @c i such that @c i and @c i+1 are both
4037	* valid iterators in @p [__first,__last) and such that
4038	* @p __binary_pred(i,(i+1)) is true, or @p __last if no such iterator
4039	* exists.
4040	*/
4041	template<typename _ForwardIterator, typename _BinaryPredicate>
4042	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
4043	inline _ForwardIterator
4044	adjacent_find(_ForwardIterator __first, _ForwardIterator __last,
4045	_BinaryPredicate __binary_pred)
4046	{
4047	// concept requirements
4048	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
4049	__glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
4050	typename iterator_traits<_ForwardIterator>::value_type,
4051	typename iterator_traits<_ForwardIterator>::value_type>)
4052	__glibcxx_requires_valid_range(__first, __last);
4053
4054	return std::__adjacent_find(__first, __last,
4055	__gnu_cxx::__ops::__iter_comp_iter(__binary_pred));
4056	}
4057
4058	/**
4059	* @brief Count the number of copies of a value in a sequence.
4060	* @ingroup non_mutating_algorithms
4061	* @param __first An input iterator.
4062	* @param __last An input iterator.
4063	* @param __value The value to be counted.
4064	* @return The number of iterators @c i in the range @p [__first,__last)
4065	* for which @c *i == @p __value
4066	*/
4067	template<typename _InputIterator, typename _Tp>
4068	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
4069	inline typename iterator_traits<_InputIterator>::difference_type
4070	count(_InputIterator __first, _InputIterator __last, const _Tp& __value)
4071	{
4072	// concept requirements
4073	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
4074	__glibcxx_function_requires(_EqualOpConcept<
4075	typename iterator_traits<_InputIterator>::value_type, _Tp>)
4076	__glibcxx_requires_valid_range(__first, __last);
4077
4078	return std::__count_if(__first, __last,
4079	__gnu_cxx::__ops::__iter_equals_val(__value));
4080	}
4081
4082	/**
4083	* @brief Count the elements of a sequence for which a predicate is true.
4084	* @ingroup non_mutating_algorithms
4085	* @param __first An input iterator.
4086	* @param __last An input iterator.
4087	* @param __pred A predicate.
4088	* @return The number of iterators @c i in the range @p [__first,__last)
4089	* for which @p __pred(*i) is true.
4090	*/
4091	template<typename _InputIterator, typename _Predicate>
4092	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
4093	inline typename iterator_traits<_InputIterator>::difference_type
4094	count_if(_InputIterator __first, _InputIterator __last, _Predicate __pred)
4095	{
4096	// concept requirements
4097	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
4098	__glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
4099	typename iterator_traits<_InputIterator>::value_type>)
4100	__glibcxx_requires_valid_range(__first, __last);
4101
4102	return std::__count_if(__first, __last,
4103	__gnu_cxx::__ops::__pred_iter(__pred));
4104	}
4105
4106	/**
4107	* @brief Search a sequence for a matching sub-sequence.
4108	* @ingroup non_mutating_algorithms
4109	* @param __first1 A forward iterator.
4110	* @param __last1 A forward iterator.
4111	* @param __first2 A forward iterator.
4112	* @param __last2 A forward iterator.
4113	* @return The first iterator @c i in the range @p
4114	* [__first1,__last1-(__last2-__first2)) such that @c *(i+N) == @p
4115	* *(__first2+N) for each @c N in the range @p
4116	* [0,__last2-__first2), or @p __last1 if no such iterator exists.
4117	*
4118	* Searches the range @p [__first1,__last1) for a sub-sequence that
4119	* compares equal value-by-value with the sequence given by @p
4120	* [__first2,__last2) and returns an iterator to the first element
4121	* of the sub-sequence, or @p __last1 if the sub-sequence is not
4122	* found.
4123	*
4124	* Because the sub-sequence must lie completely within the range @p
4125	* [__first1,__last1) it must start at a position less than @p
4126	* __last1-(__last2-__first2) where @p __last2-__first2 is the
4127	* length of the sub-sequence.
4128	*
4129	* This means that the returned iterator @c i will be in the range
4130	* @p [__first1,__last1-(__last2-__first2))
4131	*/
4132	template<typename _ForwardIterator1, typename _ForwardIterator2>
4133	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
4134	inline _ForwardIterator1
4135	search(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
4136	_ForwardIterator2 __first2, _ForwardIterator2 __last2)
4137	{
4138	// concept requirements
4139	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
4140	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
4141	__glibcxx_function_requires(_EqualOpConcept<
4142	typename iterator_traits<_ForwardIterator1>::value_type,
4143	typename iterator_traits<_ForwardIterator2>::value_type>)
4144	__glibcxx_requires_valid_range(__first1, __last1);
4145	__glibcxx_requires_valid_range(__first2, __last2);
4146
4147	return std::__search(__first1, __last1, __first2, __last2,
4148	__gnu_cxx::__ops::__iter_equal_to_iter());
4149	}
4150
4151	/**
4152	* @brief Search a sequence for a number of consecutive values.
4153	* @ingroup non_mutating_algorithms
4154	* @param __first A forward iterator.
4155	* @param __last A forward iterator.
4156	* @param __count The number of consecutive values.
4157	* @param __val The value to find.
4158	* @return The first iterator @c i in the range @p
4159	* [__first,__last-__count) such that @c *(i+N) == @p __val for
4160	* each @c N in the range @p [0,__count), or @p __last if no such
4161	* iterator exists.
4162	*
4163	* Searches the range @p [__first,__last) for @p count consecutive elements
4164	* equal to @p __val.
4165	*/
4166	template<typename _ForwardIterator, typename _Integer, typename _Tp>
4167	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
4168	inline _ForwardIterator
4169	search_n(_ForwardIterator __first, _ForwardIterator __last,
4170	_Integer __count, const _Tp& __val)
4171	{
4172	// concept requirements
4173	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
4174	__glibcxx_function_requires(_EqualOpConcept<
4175	typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
4176	__glibcxx_requires_valid_range(__first, __last);
4177
4178	return std::__search_n(__first, __last, __count,
4179	__gnu_cxx::__ops::__iter_equals_val(__val));
4180	}
4181
4182
4183	/**
4184	* @brief Search a sequence for a number of consecutive values using a
4185	* predicate.
4186	* @ingroup non_mutating_algorithms
4187	* @param __first A forward iterator.
4188	* @param __last A forward iterator.
4189	* @param __count The number of consecutive values.
4190	* @param __val The value to find.
4191	* @param __binary_pred A binary predicate.
4192	* @return The first iterator @c i in the range @p
4193	* [__first,__last-__count) such that @p
4194	* __binary_pred(*(i+N),__val) is true for each @c N in the range
4195	* @p [0,__count), or @p __last if no such iterator exists.
4196	*
4197	* Searches the range @p [__first,__last) for @p __count
4198	* consecutive elements for which the predicate returns true.
4199	*/
4200	template<typename _ForwardIterator, typename _Integer, typename _Tp,
4201	typename _BinaryPredicate>
4202	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
4203	inline _ForwardIterator
4204	search_n(_ForwardIterator __first, _ForwardIterator __last,
4205	_Integer __count, const _Tp& __val,
4206	_BinaryPredicate __binary_pred)
4207	{
4208	// concept requirements
4209	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
4210	__glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
4211	typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
4212	__glibcxx_requires_valid_range(__first, __last);
4213
4214	return std::__search_n(__first, __last, __count,
4215	__gnu_cxx::__ops::__iter_comp_val(__binary_pred, __val));
4216	}
4217
4218	#if __cplusplus >= 201703L
4219	/* @brief Search a sequence using a Searcher object.*
4220	*
4221	* @param __first A forward iterator.
4222	* @param __last A forward iterator.
4223	* @param __searcher A callable object.
4224	* @return @p __searcher(__first,__last).first
4225	*/
4226	template<typename _ForwardIterator, typename _Searcher>
4227	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
4228	inline _ForwardIterator
4229	search(_ForwardIterator __first, _ForwardIterator __last,
4230	const _Searcher& __searcher)
4231	{ return __searcher(__first, __last).first; }
4232	#endif
4233
4234	/**
4235	* @brief Perform an operation on a sequence.
4236	* @ingroup mutating_algorithms
4237	* @param __first An input iterator.
4238	* @param __last An input iterator.
4239	* @param __result An output iterator.
4240	* @param __unary_op A unary operator.
4241	* @return An output iterator equal to @p __result+(__last-__first).
4242	*
4243	* Applies the operator to each element in the input range and assigns
4244	* the results to successive elements of the output sequence.
4245	* Evaluates @p (__result+N)=unary_op((__first+N)) for each @c N in the
4246	* range @p [0,__last-__first).
4247	*
4248	* @p unary_op must not alter its argument.
4249	*/
4250	template<typename _InputIterator, typename _OutputIterator,
4251	typename _UnaryOperation>
4252	_GLIBCXX20_CONSTEXPR
4253	_OutputIterator
4254	transform(_InputIterator __first, _InputIterator __last,
4255	_OutputIterator __result, _UnaryOperation __unary_op)
4256	{
4257	// concept requirements
4258	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
4259	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4260	// "the type returned by a _UnaryOperation"
4261	__typeof__(__unary_op(*__first))>)
4262	__glibcxx_requires_valid_range(__first, __last);
4263
4264	for (; __first != __last; ++__first, (void)++__result)
4265	__result = __unary_op(__first);
4266	return __result;
4267	}
4268
4269	/**
4270	* @brief Perform an operation on corresponding elements of two sequences.
4271	* @ingroup mutating_algorithms
4272	* @param __first1 An input iterator.
4273	* @param __last1 An input iterator.
4274	* @param __first2 An input iterator.
4275	* @param __result An output iterator.
4276	* @param __binary_op A binary operator.
4277	* @return An output iterator equal to @p result+(last-first).
4278	*
4279	* Applies the operator to the corresponding elements in the two
4280	* input ranges and assigns the results to successive elements of the
4281	* output sequence.
4282	* Evaluates @p
4283	* (__result+N)=__binary_op((__first1+N),*(__first2+N)) for each
4284	* @c N in the range @p [0,__last1-__first1).
4285	*
4286	* @p binary_op must not alter either of its arguments.
4287	*/
4288	template<typename _InputIterator1, typename _InputIterator2,
4289	typename _OutputIterator, typename _BinaryOperation>
4290	_GLIBCXX20_CONSTEXPR
4291	_OutputIterator
4292	transform(_InputIterator1 __first1, _InputIterator1 __last1,
4293	_InputIterator2 __first2, _OutputIterator __result,
4294	_BinaryOperation __binary_op)
4295	{
4296	// concept requirements
4297	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
4298	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
4299	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4300	// "the type returned by a _BinaryOperation"
4301	__typeof__(__binary_op(__first1,__first2))>)
4302	__glibcxx_requires_valid_range(__first1, __last1);
4303
4304	for (; __first1 != __last1; ++__first1, (void)++__first2, ++__result)
4305	__result = __binary_op(__first1, *__first2);
4306	return __result;
4307	}
4308
4309	/**
4310	* @brief Replace each occurrence of one value in a sequence with another
4311	* value.
4312	* @ingroup mutating_algorithms
4313	* @param __first A forward iterator.
4314	* @param __last A forward iterator.
4315	* @param __old_value The value to be replaced.
4316	* @param __new_value The replacement value.
4317	* @return replace() returns no value.
4318	*
4319	* For each iterator `i` in the range `[__first,__last)` if
4320	* `i == __old_value` then the assignment `i = __new_value` is performed.
4321	*/
4322	template<typename _ForwardIterator, typename _Tp>
4323	_GLIBCXX20_CONSTEXPR
4324	void
4325	replace(_ForwardIterator __first, _ForwardIterator __last,
4326	const _Tp& __old_value, const _Tp& __new_value)
4327	{
4328	// concept requirements
4329	__glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
4330	_ForwardIterator>)
4331	__glibcxx_function_requires(_EqualOpConcept<
4332	typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
4333	__glibcxx_function_requires(_ConvertibleConcept<_Tp,
4334	typename iterator_traits<_ForwardIterator>::value_type>)
4335	__glibcxx_requires_valid_range(__first, __last);
4336
4337	for (; __first != __last; ++__first)
4338	if (*__first == __old_value)
4339	*__first = __new_value;
4340	}
4341
4342	/**
4343	* @brief Replace each value in a sequence for which a predicate returns
4344	* true with another value.
4345	* @ingroup mutating_algorithms
4346	* @param __first A forward iterator.
4347	* @param __last A forward iterator.
4348	* @param __pred A predicate.
4349	* @param __new_value The replacement value.
4350	* @return replace_if() returns no value.
4351	*
4352	* For each iterator `i` in the range `[__first,__last)` if `__pred(*i)`
4353	* is true then the assignment `*i = __new_value` is performed.
4354	*/
4355	template<typename _ForwardIterator, typename _Predicate, typename _Tp>
4356	_GLIBCXX20_CONSTEXPR
4357	void
4358	replace_if(_ForwardIterator __first, _ForwardIterator __last,
4359	_Predicate __pred, const _Tp& __new_value)
4360	{
4361	// concept requirements
4362	__glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
4363	_ForwardIterator>)
4364	__glibcxx_function_requires(_ConvertibleConcept<_Tp,
4365	typename iterator_traits<_ForwardIterator>::value_type>)
4366	__glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
4367	typename iterator_traits<_ForwardIterator>::value_type>)
4368	__glibcxx_requires_valid_range(__first, __last);
4369
4370	for (; __first != __last; ++__first)
4371	if (__pred(*__first))
4372	*__first = __new_value;
4373	}
4374
4375	/**
4376	* @brief Assign the result of a function object to each value in a
4377	* sequence.
4378	* @ingroup mutating_algorithms
4379	* @param __first A forward iterator.
4380	* @param __last A forward iterator.
4381	* @param __gen A function object callable with no arguments.
4382	* @return generate() returns no value.
4383	*
4384	* Performs the assignment `*i = __gen()` for each `i` in the range
4385	* `[__first, __last)`.
4386	*/
4387	template<typename _ForwardIterator, typename _Generator>
4388	_GLIBCXX20_CONSTEXPR
4389	void
4390	generate(_ForwardIterator __first, _ForwardIterator __last,
4391	_Generator __gen)
4392	{
4393	// concept requirements
4394	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
4395	__glibcxx_function_requires(_GeneratorConcept<_Generator,
4396	typename iterator_traits<_ForwardIterator>::value_type>)
4397	__glibcxx_requires_valid_range(__first, __last);
4398
4399	for (; __first != __last; ++__first)
4400	*__first = __gen();
4401	}
4402
4403	/**
4404	* @brief Assign the result of a function object to each value in a
4405	* sequence.
4406	* @ingroup mutating_algorithms
4407	* @param __first A forward iterator.
4408	* @param __n The length of the sequence.
4409	* @param __gen A function object callable with no arguments.
4410	* @return The end of the sequence, i.e., `__first + __n`
4411	*
4412	* Performs the assignment `*i = __gen()` for each `i` in the range
4413	* `[__first, __first + __n)`.
4414	*
4415	* If `__n` is negative, the function does nothing and returns `__first`.
4416	*/
4417	// _GLIBCXX_RESOLVE_LIB_DEFECTS
4418	// DR 865. More algorithms that throw away information
4419	// DR 426. search_n(), fill_n(), and generate_n() with negative n
4420	template<typename _OutputIterator, typename _Size, typename _Generator>
4421	_GLIBCXX20_CONSTEXPR
4422	_OutputIterator
4423	generate_n(_OutputIterator __first, _Size __n, _Generator __gen)
4424	{
4425	// concept requirements
4426	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4427	// "the type returned by a _Generator"
4428	__typeof__(__gen())>)
4429
4430	typedef __decltype(std::__size_to_integer(__n)) _IntSize;
4431	for (_IntSize __niter = std::__size_to_integer(__n);
4432	__niter > `0`; --__niter, (void) ++__first)
4433	*__first = __gen();
4434	return __first;
4435	}
4436
4437	/**
4438	* @brief Copy a sequence, removing consecutive duplicate values.
4439	* @ingroup mutating_algorithms
4440	* @param __first An input iterator.
4441	* @param __last An input iterator.
4442	* @param __result An output iterator.
4443	* @return An iterator designating the end of the resulting sequence.
4444	*
4445	* Copies each element in the range `[__first, __last)` to the range
4446	* beginning at `__result`, except that only the first element is copied
4447	* from groups of consecutive elements that compare equal.
4448	* `unique_copy()` is stable, so the relative order of elements that are
4449	* copied is unchanged.
4450	*/
4451	// _GLIBCXX_RESOLVE_LIB_DEFECTS
4452	// DR 241. Does unique_copy() require CopyConstructible and Assignable?
4453	// DR 538. 241 again: Does unique_copy() require CopyConstructible and
4454	// Assignable?
4455	template<typename _InputIterator, typename _OutputIterator>
4456	_GLIBCXX20_CONSTEXPR
4457	inline _OutputIterator
4458	unique_copy(_InputIterator __first, _InputIterator __last,
4459	_OutputIterator __result)
4460	{
4461	// concept requirements
4462	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
4463	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4464	typename iterator_traits<_InputIterator>::value_type>)
4465	__glibcxx_function_requires(_EqualityComparableConcept<
4466	typename iterator_traits<_InputIterator>::value_type>)
4467	__glibcxx_requires_valid_range(__first, __last);
4468
4469	if (__first == __last)
4470	return __result;
4471	return std::__unique_copy(__first, __last, __result,
4472	__gnu_cxx::__ops::__iter_equal_to_iter(),
4473	std::__iterator_category(__first),
4474	std::__iterator_category(__result));
4475	}
4476
4477	/**
4478	* @brief Copy a sequence, removing consecutive values using a predicate.
4479	* @ingroup mutating_algorithms
4480	* @param __first An input iterator.
4481	* @param __last An input iterator.
4482	* @param __result An output iterator.
4483	* @param __binary_pred A binary predicate.
4484	* @return An iterator designating the end of the resulting sequence.
4485	*
4486	* Copies each element in the range `[__first, __last)` to the range
4487	* beginning at `__result`, except that only the first element is copied
4488	* from groups of consecutive elements for which `__binary_pred` returns
4489	* true.
4490	* `unique_copy()` is stable, so the relative order of elements that are
4491	* copied is unchanged.
4492	*/
4493	// _GLIBCXX_RESOLVE_LIB_DEFECTS
4494	// DR 241. Does unique_copy() require CopyConstructible and Assignable?
4495	template<typename _InputIterator, typename _OutputIterator,
4496	typename _BinaryPredicate>
4497	_GLIBCXX20_CONSTEXPR
4498	inline _OutputIterator
4499	unique_copy(_InputIterator __first, _InputIterator __last,
4500	_OutputIterator __result,
4501	_BinaryPredicate __binary_pred)
4502	{
4503	// concept requirements -- predicates checked later
4504	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
4505	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4506	typename iterator_traits<_InputIterator>::value_type>)
4507	__glibcxx_requires_valid_range(__first, __last);
4508
4509	if (__first == __last)
4510	return __result;
4511	return std::__unique_copy(__first, __last, __result,
4512	__gnu_cxx::__ops::__iter_comp_iter(__binary_pred),
4513	std::__iterator_category(__first),
4514	std::__iterator_category(__result));
4515	}
4516
4517	#if __cplusplus <= 201103L \|\| _GLIBCXX_USE_DEPRECATED
4518	#if _GLIBCXX_HOSTED
4519	/**
4520	* @brief Randomly shuffle the elements of a sequence.
4521	* @ingroup mutating_algorithms
4522	* @param __first A forward iterator.
4523	* @param __last A forward iterator.
4524	* @return Nothing.
4525	*
4526	* Reorder the elements in the range `[__first, __last)` using a random
4527	* distribution, so that every possible ordering of the sequence is
4528	* equally likely.
4529	*
4530	* @deprecated
4531	* Since C++17, `std::random_shuffle` is not part of the C++ standard.
4532	* Use `std::shuffle` instead, which was introduced in C++11.
4533	*/
4534	template<typename _RandomAccessIterator>
4535	_GLIBCXX14_DEPRECATED_SUGGEST("std::shuffle")
4536	inline void
4537	random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last)
4538	{
4539	// concept requirements
4540	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4541	_RandomAccessIterator>)
4542	__glibcxx_requires_valid_range(__first, __last);
4543
4544	if (__first == __last)
4545	return;
4546
4547	#if RAND_MAX < __INT_MAX__
4548	if (__builtin_expect((__last - __first) >= RAND_MAX / `4`, `0`))
4549	{
4550	// Use a xorshift implementation seeded by two calls to rand()
4551	// instead of using rand() for all the random numbers needed.
4552	unsigned __xss
4553	= (unsigned)std::rand() ^ ((unsigned)std::rand() << `15`);
4554	for (_RandomAccessIterator __i = __first + `1`; __i != __last; ++__i)
4555	{
4556	__xss += !__xss;
4557	__xss ^= __xss << `13`;
4558	__xss ^= __xss >> `17`;
4559	__xss ^= __xss << `5`;
4560	_RandomAccessIterator __j = __first
4561	+ (__xss % ((__i - __first) + `1`));
4562	if (__i != __j)
4563	std::iter_swap(__i, __j);
4564	}
4565	return;
4566	}
4567	#endif
4568
4569	for (_RandomAccessIterator __i = __first + `1`; __i != __last; ++__i)
4570	{
4571	// XXX rand() % N is not uniformly distributed
4572	_RandomAccessIterator __j = __first
4573	+ (std::rand() % ((__i - __first) + `1`));
4574	if (__i != __j)
4575	std::iter_swap(__i, __j);
4576	}
4577	}
4578
4579	/**
4580	* @brief Shuffle the elements of a sequence using a random number
4581	* generator.
4582	* @ingroup mutating_algorithms
4583	* @param __first A forward iterator.
4584	* @param __last A forward iterator.
4585	* @param __rand The RNG functor or function.
4586	* @return Nothing.
4587	*
4588	* Reorders the elements in the range `[__first, __last)` using `__rand`
4589	* to provide a random distribution. Calling `__rand(N)` for a positive
4590	* integer `N` should return a randomly chosen integer from the
4591	* range `[0, N)`.
4592	*
4593	* @deprecated
4594	* Since C++17, `std::random_shuffle` is not part of the C++ standard.
4595	* Use `std::shuffle` instead, which was introduced in C++11.
4596	*/
4597	template<typename _RandomAccessIterator, typename _RandomNumberGenerator>
4598	_GLIBCXX14_DEPRECATED_SUGGEST("std::shuffle")
4599	void
4600	random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last,
4601	#if __cplusplus >= 201103L
4602	_RandomNumberGenerator&& __rand)
4603	#else
4604	_RandomNumberGenerator& __rand)
4605	#endif
4606	{
4607	// concept requirements
4608	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4609	_RandomAccessIterator>)
4610	__glibcxx_requires_valid_range(__first, __last);
4611
4612	if (__first == __last)
4613	return;
4614	for (_RandomAccessIterator __i = __first + `1`; __i != __last; ++__i)
4615	{
4616	_RandomAccessIterator __j = __first + __rand((__i - __first) + `1`);
4617	if (__i != __j)
4618	std::iter_swap(__i, __j);
4619	}
4620	}
4621	#endif // HOSTED
4622	#endif // <= C++11 \|\| USE_DEPRECATED
4623
4624	/**
4625	* @brief Move elements for which a predicate is true to the beginning
4626	* of a sequence.
4627	* @ingroup mutating_algorithms
4628	* @param __first A forward iterator.
4629	* @param __last A forward iterator.
4630	* @param __pred A predicate functor.
4631	* @return An iterator `middle` such that `__pred(i)` is true for each
4632	* iterator `i` in the range `[__first, middle)` and false for each `i`
4633	* in the range `[middle, __last)`.
4634	*
4635	* `__pred` must not modify its operand. `partition()` does not preserve
4636	* the relative ordering of elements in each group, use
4637	* `stable_partition()` if this is needed.
4638	*/
4639	template<typename _ForwardIterator, typename _Predicate>
4640	_GLIBCXX20_CONSTEXPR
4641	inline _ForwardIterator
4642	partition(_ForwardIterator __first, _ForwardIterator __last,
4643	_Predicate __pred)
4644	{
4645	// concept requirements
4646	__glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
4647	_ForwardIterator>)
4648	__glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
4649	typename iterator_traits<_ForwardIterator>::value_type>)
4650	__glibcxx_requires_valid_range(__first, __last);
4651
4652	return std::__partition(__first, __last, __pred,
4653	std::__iterator_category(__first));
4654	}
4655
4656
4657	/**
4658	* @brief Sort the smallest elements of a sequence.
4659	* @ingroup sorting_algorithms
4660	* @param __first An iterator.
4661	* @param __middle Another iterator.
4662	* @param __last Another iterator.
4663	* @return Nothing.
4664	*
4665	* Sorts the smallest `(__middle - __first)` elements in the range
4666	* `[first, last)` and moves them to the range `[__first, __middle)`. The
4667	* order of the remaining elements in the range `[__middle, __last)` is
4668	* unspecified.
4669	* After the sort if `i` and `j` are iterators in the range
4670	* `[__first, __middle)` such that `i` precedes `j` and `k` is an iterator
4671	* in the range `[__middle, __last)` then `j < i` and `k < i` are
4672	* both false.
4673	*/
4674	template<typename _RandomAccessIterator>
4675	_GLIBCXX20_CONSTEXPR
4676	inline void
4677	partial_sort(_RandomAccessIterator __first,
4678	_RandomAccessIterator __middle,
4679	_RandomAccessIterator __last)
4680	{
4681	// concept requirements
4682	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4683	_RandomAccessIterator>)
4684	__glibcxx_function_requires(_LessThanComparableConcept<
4685	typename iterator_traits<_RandomAccessIterator>::value_type>)
4686	__glibcxx_requires_valid_range(__first, __middle);
4687	__glibcxx_requires_valid_range(__middle, __last);
4688	__glibcxx_requires_irreflexive(__first, __last);
4689
4690	std::__partial_sort(__first, __middle, __last,
4691	__gnu_cxx::__ops::__iter_less_iter());
4692	}
4693
4694	/**
4695	* @brief Sort the smallest elements of a sequence using a predicate
4696	* for comparison.
4697	* @ingroup sorting_algorithms
4698	* @param __first An iterator.
4699	* @param __middle Another iterator.
4700	* @param __last Another iterator.
4701	* @param __comp A comparison functor.
4702	* @return Nothing.
4703	*
4704	* Sorts the smallest `(__middle - __first)` elements in the range
4705	* `[__first, __last)` and moves them to the range `[__first, __middle)`.
4706	* The order of the remaining elements in the range `[__middle, __last)` is
4707	* unspecified.
4708	* After the sort if `i` and `j` are iterators in the range
4709	* `[__first, __middle)` such that `i` precedes `j` and `k` is an iterator
4710	* in the range `[__middle, __last)` then `__comp(j, i)` and
4711	* `__comp(k, i)` are both false.
4712	*/
4713	template<typename _RandomAccessIterator, typename _Compare>
4714	_GLIBCXX20_CONSTEXPR
4715	inline void
4716	partial_sort(_RandomAccessIterator __first,
4717	_RandomAccessIterator __middle,
4718	_RandomAccessIterator __last,
4719	_Compare __comp)
4720	{
4721	// concept requirements
4722	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4723	_RandomAccessIterator>)
4724	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
4725	typename iterator_traits<_RandomAccessIterator>::value_type,
4726	typename iterator_traits<_RandomAccessIterator>::value_type>)
4727	__glibcxx_requires_valid_range(__first, __middle);
4728	__glibcxx_requires_valid_range(__middle, __last);
4729	__glibcxx_requires_irreflexive_pred(__first, __last, __comp);
4730
4731	std::__partial_sort(__first, __middle, __last,
4732	__gnu_cxx::__ops::__iter_comp_iter(__comp));
4733	}
4734
4735	/**
4736	* @brief Sort a sequence just enough to find a particular position.
4737	* @ingroup sorting_algorithms
4738	* @param __first An iterator.
4739	* @param __nth Another iterator.
4740	* @param __last Another iterator.
4741	* @return Nothing.
4742	*
4743	* Rearranges the elements in the range `[__first, __last)` so that `*__nth`
4744	* is the same element that would have been in that position had the
4745	* whole sequence been sorted. The elements either side of `*__nth` are
4746	* not completely sorted, but for any iterator `i` in the range
4747	* `[__first, __nth)` and any iterator `j` in the range `[__nth, __last)` it
4748	* holds that `j < i` is false.
4749	*/
4750	template<typename _RandomAccessIterator>
4751	_GLIBCXX20_CONSTEXPR
4752	inline void
4753	nth_element(_RandomAccessIterator __first, _RandomAccessIterator __nth,
4754	_RandomAccessIterator __last)
4755	{
4756	// concept requirements
4757	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4758	_RandomAccessIterator>)
4759	__glibcxx_function_requires(_LessThanComparableConcept<
4760	typename iterator_traits<_RandomAccessIterator>::value_type>)
4761	__glibcxx_requires_valid_range(__first, __nth);
4762	__glibcxx_requires_valid_range(__nth, __last);
4763	__glibcxx_requires_irreflexive(__first, __last);
4764
4765	if (__first == __last \|\| __nth == __last)
4766	return;
4767
4768	std::__introselect(__first, __nth, __last,
4769	std::__lg(__last - __first) * `2`,
4770	__gnu_cxx::__ops::__iter_less_iter());
4771	}
4772
4773	/**
4774	* @brief Sort a sequence just enough to find a particular position
4775	* using a predicate for comparison.
4776	* @ingroup sorting_algorithms
4777	* @param __first An iterator.
4778	* @param __nth Another iterator.
4779	* @param __last Another iterator.
4780	* @param __comp A comparison functor.
4781	* @return Nothing.
4782	*
4783	* Rearranges the elements in the range `[__first, __last)` so that `*__nth`
4784	* is the same element that would have been in that position had the
4785	* whole sequence been sorted. The elements either side of `*__nth` are
4786	* not completely sorted, but for any iterator `i` in the range
4787	* `[__first, __nth)` and any iterator `j` in the range `[__nth, __last)`
4788	* it holds that `__comp(j, i)` is false.
4789	*/
4790	template<typename _RandomAccessIterator, typename _Compare>
4791	_GLIBCXX20_CONSTEXPR
4792	inline void
4793	nth_element(_RandomAccessIterator __first, _RandomAccessIterator __nth,
4794	_RandomAccessIterator __last, _Compare __comp)
4795	{
4796	// concept requirements
4797	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4798	_RandomAccessIterator>)
4799	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
4800	typename iterator_traits<_RandomAccessIterator>::value_type,
4801	typename iterator_traits<_RandomAccessIterator>::value_type>)
4802	__glibcxx_requires_valid_range(__first, __nth);
4803	__glibcxx_requires_valid_range(__nth, __last);
4804	__glibcxx_requires_irreflexive_pred(__first, __last, __comp);
4805
4806	if (__first == __last \|\| __nth == __last)
4807	return;
4808
4809	std::__introselect(__first, __nth, __last,
4810	std::__lg(__last - __first) * `2`,
4811	__gnu_cxx::__ops::__iter_comp_iter(__comp));
4812	}
4813
4814	/**
4815	* @brief Sort the elements of a sequence.
4816	* @ingroup sorting_algorithms
4817	* @param __first An iterator.
4818	* @param __last Another iterator.
4819	* @return Nothing.
4820	*
4821	* Sorts the elements in the range `[__first, __last)` in ascending order,
4822	* such that for each iterator `i` in the range `[__first, __last - 1)`,
4823	* `(i+1) < i` is false.
4824	*
4825	* The relative ordering of equivalent elements is not preserved, use
4826	* `stable_sort()` if this is needed.
4827	*/
4828	template<typename _RandomAccessIterator>
4829	_GLIBCXX20_CONSTEXPR
4830	inline void
4831	sort(_RandomAccessIterator __first, _RandomAccessIterator __last)
4832	{
4833	// concept requirements
4834	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4835	_RandomAccessIterator>)
4836	__glibcxx_function_requires(_LessThanComparableConcept<
4837	typename iterator_traits<_RandomAccessIterator>::value_type>)
4838	__glibcxx_requires_valid_range(__first, __last);
4839	__glibcxx_requires_irreflexive(__first, __last);
4840
4841	std::__sort(__first, __last, __gnu_cxx::__ops::__iter_less_iter());
4842	}
4843
4844	/**
4845	* @brief Sort the elements of a sequence using a predicate for comparison.
4846	* @ingroup sorting_algorithms
4847	* @param __first An iterator.
4848	* @param __last Another iterator.
4849	* @param __comp A comparison functor.
4850	* @return Nothing.
4851	*
4852	* Sorts the elements in the range `[__first, __last)` in ascending order,
4853	* such that `__comp((i+1), i)` is false for every iterator `i` in the
4854	* range `[__first, __last - 1)`.
4855	*
4856	* The relative ordering of equivalent elements is not preserved, use
4857	* `stable_sort()` if this is needed.
4858	*/
4859	template<typename _RandomAccessIterator, typename _Compare>
4860	_GLIBCXX20_CONSTEXPR
4861	inline void
4862	sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
4863	_Compare __comp)
4864	{
4865	// concept requirements
4866	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4867	_RandomAccessIterator>)
4868	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
4869	typename iterator_traits<_RandomAccessIterator>::value_type,
4870	typename iterator_traits<_RandomAccessIterator>::value_type>)
4871	__glibcxx_requires_valid_range(__first, __last);
4872	__glibcxx_requires_irreflexive_pred(__first, __last, __comp);
4873
4874	std::__sort(__first, __last, __gnu_cxx::__ops::__iter_comp_iter(__comp));
4875	}
4876
4877	template<typename _InputIterator1, typename _InputIterator2,
4878	typename _OutputIterator, typename _Compare>
4879	_GLIBCXX20_CONSTEXPR
4880	_OutputIterator
4881	__merge(_InputIterator1 __first1, _InputIterator1 __last1,
4882	_InputIterator2 __first2, _InputIterator2 __last2,
4883	_OutputIterator __result, _Compare __comp)
4884	{
4885	while (__first1 != __last1 && __first2 != __last2)
4886	{
4887	if (__comp(__first2, __first1))
4888	{
4889	__result = __first2;
4890	++__first2;
4891	}
4892	else
4893	{
4894	__result = __first1;
4895	++__first1;
4896	}
4897	++__result;
4898	}
4899	return std::copy(__first2, __last2,
4900	std::copy(__first1, __last1, __result));
4901	}
4902
4903	/**
4904	* @brief Merges two sorted ranges.
4905	* @ingroup sorting_algorithms
4906	* @param __first1 An iterator.
4907	* @param __first2 Another iterator.
4908	* @param __last1 Another iterator.
4909	* @param __last2 Another iterator.
4910	* @param __result An iterator pointing to the end of the merged range.
4911	* @return An output iterator equal to @p __result + (__last1 - __first1)
4912	* + (__last2 - __first2).
4913	*
4914	* Merges the ranges @p [__first1,__last1) and @p [__first2,__last2) into
4915	* the sorted range @p [__result, __result + (__last1-__first1) +
4916	* (__last2-__first2)). Both input ranges must be sorted, and the
4917	* output range must not overlap with either of the input ranges.
4918	* The sort is @e stable, that is, for equivalent elements in the
4919	* two ranges, elements from the first range will always come
4920	* before elements from the second.
4921	*/
4922	template<typename _InputIterator1, typename _InputIterator2,
4923	typename _OutputIterator>
4924	_GLIBCXX20_CONSTEXPR
4925	inline _OutputIterator
4926	merge(_InputIterator1 __first1, _InputIterator1 __last1,
4927	_InputIterator2 __first2, _InputIterator2 __last2,
4928	_OutputIterator __result)
4929	{
4930	// concept requirements
4931	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
4932	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
4933	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4934	typename iterator_traits<_InputIterator1>::value_type>)
4935	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4936	typename iterator_traits<_InputIterator2>::value_type>)
4937	__glibcxx_function_requires(_LessThanOpConcept<
4938	typename iterator_traits<_InputIterator2>::value_type,
4939	typename iterator_traits<_InputIterator1>::value_type>)
4940	__glibcxx_requires_sorted_set(__first1, __last1, __first2);
4941	__glibcxx_requires_sorted_set(__first2, __last2, __first1);
4942	__glibcxx_requires_irreflexive2(__first1, __last1);
4943	__glibcxx_requires_irreflexive2(__first2, __last2);
4944
4945	return _GLIBCXX_STD_A::__merge(__first1, __last1,
4946	__first2, __last2, __result,
4947	__gnu_cxx::__ops::__iter_less_iter());
4948	}
4949
4950	/**
4951	* @brief Merges two sorted ranges.
4952	* @ingroup sorting_algorithms
4953	* @param __first1 An iterator.
4954	* @param __first2 Another iterator.
4955	* @param __last1 Another iterator.
4956	* @param __last2 Another iterator.
4957	* @param __result An iterator pointing to the end of the merged range.
4958	* @param __comp A functor to use for comparisons.
4959	* @return An output iterator equal to @p __result + (__last1 - __first1)
4960	* + (__last2 - __first2).
4961	*
4962	* Merges the ranges @p [__first1,__last1) and @p [__first2,__last2) into
4963	* the sorted range @p [__result, __result + (__last1-__first1) +
4964	* (__last2-__first2)). Both input ranges must be sorted, and the
4965	* output range must not overlap with either of the input ranges.
4966	* The sort is @e stable, that is, for equivalent elements in the
4967	* two ranges, elements from the first range will always come
4968	* before elements from the second.
4969	*
4970	* The comparison function should have the same effects on ordering as
4971	* the function used for the initial sort.
4972	*/
4973	template<typename _InputIterator1, typename _InputIterator2,
4974	typename _OutputIterator, typename _Compare>
4975	_GLIBCXX20_CONSTEXPR
4976	inline _OutputIterator
4977	merge(_InputIterator1 __first1, _InputIterator1 __last1,
4978	_InputIterator2 __first2, _InputIterator2 __last2,
4979	_OutputIterator __result, _Compare __comp)
4980	{
4981	// concept requirements
4982	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
4983	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
4984	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4985	typename iterator_traits<_InputIterator1>::value_type>)
4986	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4987	typename iterator_traits<_InputIterator2>::value_type>)
4988	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
4989	typename iterator_traits<_InputIterator2>::value_type,
4990	typename iterator_traits<_InputIterator1>::value_type>)
4991	__glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
4992	__glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);
4993	__glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
4994	__glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);
4995
4996	return _GLIBCXX_STD_A::__merge(__first1, __last1,
4997	__first2, __last2, __result,
4998	__gnu_cxx::__ops::__iter_comp_iter(__comp));
4999	}
5000
5001	template<typename _RandomAccessIterator, typename _Compare>
5002	_GLIBCXX26_CONSTEXPR
5003	inline void
5004	__stable_sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
5005	_Compare __comp)
5006	{
5007	typedef typename iterator_traits<_RandomAccessIterator>::value_type
5008	_ValueType;
5009	typedef typename iterator_traits<_RandomAccessIterator>::difference_type
5010	_DistanceType;
5011
5012	if (__first == __last)
5013	return;
5014
5015	#if _GLIBCXX_HOSTED
5016	# if __glibcxx_constexpr_algorithms >= 202306L // >= C++26
5017	if consteval {
5018	return std::__inplace_stable_sort(__first, __last, __comp);
5019	}
5020	# endif
5021
5022	typedef _Temporary_buffer<_RandomAccessIterator, _ValueType> _TmpBuf;
5023	// __stable_sort_adaptive sorts the range in two halves,
5024	// so the buffer only needs to fit half the range at once.
5025	_TmpBuf __buf(__first, (__last - __first + `1`) / `2`);
5026
5027	if (__builtin_expect(__buf.requested_size() == __buf.size(), true))
5028	std::__stable_sort_adaptive(__first,
5029	__first + _DistanceType(__buf.size()),
5030	__last, __buf.begin(), __comp);
5031	else if (__builtin_expect(__buf.begin() == `0`, false))
5032	std::__inplace_stable_sort(__first, __last, __comp);
5033	else
5034	std::__stable_sort_adaptive_resize(__first, __last, __buf.begin(),
5035	_DistanceType(__buf.size()), __comp);
5036	#else
5037	std::__inplace_stable_sort(__first, __last, __comp);
5038	#endif
5039	}
5040
5041	/**
5042	* @brief Sort the elements of a sequence, preserving the relative order
5043	* of equivalent elements.
5044	* @ingroup sorting_algorithms
5045	* @param __first An iterator.
5046	* @param __last Another iterator.
5047	* @return Nothing.
5048	*
5049	* Sorts the elements in the range @p [__first,__last) in ascending order,
5050	* such that for each iterator @p i in the range @p [__first,__last-1),
5051	* @p (i+1)<i is false.
5052	*
5053	* The relative ordering of equivalent elements is preserved, so any two
5054	* elements @p x and @p y in the range @p [__first,__last) such that
5055	* @p x<y is false and @p y<x is false will have the same relative
5056	* ordering after calling @p stable_sort().
5057	*/
5058	template<typename _RandomAccessIterator>
5059	_GLIBCXX26_CONSTEXPR
5060	inline void
5061	stable_sort(_RandomAccessIterator __first, _RandomAccessIterator __last)
5062	{
5063	// concept requirements
5064	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
5065	_RandomAccessIterator>)
5066	__glibcxx_function_requires(_LessThanComparableConcept<
5067	typename iterator_traits<_RandomAccessIterator>::value_type>)
5068	__glibcxx_requires_valid_range(__first, __last);
5069	__glibcxx_requires_irreflexive(__first, __last);
5070
5071	_GLIBCXX_STD_A::__stable_sort(__first, __last,
5072	__gnu_cxx::__ops::__iter_less_iter());
5073	}
5074
5075	/**
5076	* @brief Sort the elements of a sequence using a predicate for comparison,
5077	* preserving the relative order of equivalent elements.
5078	* @ingroup sorting_algorithms
5079	* @param __first An iterator.
5080	* @param __last Another iterator.
5081	* @param __comp A comparison functor.
5082	* @return Nothing.
5083	*
5084	* Sorts the elements in the range @p [__first,__last) in ascending order,
5085	* such that for each iterator @p i in the range @p [__first,__last-1),
5086	* @p __comp((i+1),i) is false.
5087	*
5088	* The relative ordering of equivalent elements is preserved, so any two
5089	* elements @p x and @p y in the range @p [__first,__last) such that
5090	* @p __comp(x,y) is false and @p __comp(y,x) is false will have the same
5091	* relative ordering after calling @p stable_sort().
5092	*/
5093	template<typename _RandomAccessIterator, typename _Compare>
5094	_GLIBCXX26_CONSTEXPR
5095	inline void
5096	stable_sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
5097	_Compare __comp)
5098	{
5099	// concept requirements
5100	__glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
5101	_RandomAccessIterator>)
5102	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5103	typename iterator_traits<_RandomAccessIterator>::value_type,
5104	typename iterator_traits<_RandomAccessIterator>::value_type>)
5105	__glibcxx_requires_valid_range(__first, __last);
5106	__glibcxx_requires_irreflexive_pred(__first, __last, __comp);
5107
5108	_GLIBCXX_STD_A::__stable_sort(__first, __last,
5109	__gnu_cxx::__ops::__iter_comp_iter(__comp));
5110	}
5111
5112	template<typename _InputIterator1, typename _InputIterator2,
5113	typename _OutputIterator,
5114	typename _Compare>
5115	_GLIBCXX20_CONSTEXPR
5116	_OutputIterator
5117	__set_union(_InputIterator1 __first1, _InputIterator1 __last1,
5118	_InputIterator2 __first2, _InputIterator2 __last2,
5119	_OutputIterator __result, _Compare __comp)
5120	{
5121	while (__first1 != __last1 && __first2 != __last2)
5122	{
5123	if (__comp(__first1, __first2))
5124	{
5125	__result = __first1;
5126	++__first1;
5127	}
5128	else if (__comp(__first2, __first1))
5129	{
5130	__result = __first2;
5131	++__first2;
5132	}
5133	else
5134	{
5135	__result = __first1;
5136	++__first1;
5137	++__first2;
5138	}
5139	++__result;
5140	}
5141	return std::copy(__first2, __last2,
5142	std::copy(__first1, __last1, __result));
5143	}
5144
5145	/**
5146	* @brief Return the union of two sorted ranges.
5147	* @ingroup set_algorithms
5148	* @param __first1 Start of first range.
5149	* @param __last1 End of first range.
5150	* @param __first2 Start of second range.
5151	* @param __last2 End of second range.
5152	* @param __result Start of output range.
5153	* @return End of the output range.
5154	* @ingroup set_algorithms
5155	*
5156	* This operation iterates over both ranges, copying elements present in
5157	* each range in order to the output range. Iterators increment for each
5158	* range. When the current element of one range is less than the other,
5159	* that element is copied and the iterator advanced. If an element is
5160	* contained in both ranges, the element from the first range is copied and
5161	* both ranges advance. The output range may not overlap either input
5162	* range.
5163	*/
5164	template<typename _InputIterator1, typename _InputIterator2,
5165	typename _OutputIterator>
5166	_GLIBCXX20_CONSTEXPR
5167	inline _OutputIterator
5168	set_union(_InputIterator1 __first1, _InputIterator1 __last1,
5169	_InputIterator2 __first2, _InputIterator2 __last2,
5170	_OutputIterator __result)
5171	{
5172	// concept requirements
5173	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5174	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5175	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5176	typename iterator_traits<_InputIterator1>::value_type>)
5177	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5178	typename iterator_traits<_InputIterator2>::value_type>)
5179	__glibcxx_function_requires(_LessThanOpConcept<
5180	typename iterator_traits<_InputIterator1>::value_type,
5181	typename iterator_traits<_InputIterator2>::value_type>)
5182	__glibcxx_function_requires(_LessThanOpConcept<
5183	typename iterator_traits<_InputIterator2>::value_type,
5184	typename iterator_traits<_InputIterator1>::value_type>)
5185	__glibcxx_requires_sorted_set(__first1, __last1, __first2);
5186	__glibcxx_requires_sorted_set(__first2, __last2, __first1);
5187	__glibcxx_requires_irreflexive2(__first1, __last1);
5188	__glibcxx_requires_irreflexive2(__first2, __last2);
5189
5190	return _GLIBCXX_STD_A::__set_union(__first1, __last1,
5191	__first2, __last2, __result,
5192	__gnu_cxx::__ops::__iter_less_iter());
5193	}
5194
5195	/**
5196	* @brief Return the union of two sorted ranges using a comparison functor.
5197	* @ingroup set_algorithms
5198	* @param __first1 Start of first range.
5199	* @param __last1 End of first range.
5200	* @param __first2 Start of second range.
5201	* @param __last2 End of second range.
5202	* @param __result Start of output range.
5203	* @param __comp The comparison functor.
5204	* @return End of the output range.
5205	* @ingroup set_algorithms
5206	*
5207	* This operation iterates over both ranges, copying elements present in
5208	* each range in order to the output range. Iterators increment for each
5209	* range. When the current element of one range is less than the other
5210	* according to @p __comp, that element is copied and the iterator advanced.
5211	* If an equivalent element according to @p __comp is contained in both
5212	* ranges, the element from the first range is copied and both ranges
5213	* advance. The output range may not overlap either input range.
5214	*/
5215	template<typename _InputIterator1, typename _InputIterator2,
5216	typename _OutputIterator, typename _Compare>
5217	_GLIBCXX20_CONSTEXPR
5218	inline _OutputIterator
5219	set_union(_InputIterator1 __first1, _InputIterator1 __last1,
5220	_InputIterator2 __first2, _InputIterator2 __last2,
5221	_OutputIterator __result, _Compare __comp)
5222	{
5223	// concept requirements
5224	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5225	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5226	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5227	typename iterator_traits<_InputIterator1>::value_type>)
5228	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5229	typename iterator_traits<_InputIterator2>::value_type>)
5230	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5231	typename iterator_traits<_InputIterator1>::value_type,
5232	typename iterator_traits<_InputIterator2>::value_type>)
5233	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5234	typename iterator_traits<_InputIterator2>::value_type,
5235	typename iterator_traits<_InputIterator1>::value_type>)
5236	__glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
5237	__glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);
5238	__glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
5239	__glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);
5240
5241	return _GLIBCXX_STD_A::__set_union(__first1, __last1,
5242	__first2, __last2, __result,
5243	__gnu_cxx::__ops::__iter_comp_iter(__comp));
5244	}
5245
5246	template<typename _InputIterator1, typename _InputIterator2,
5247	typename _OutputIterator,
5248	typename _Compare>
5249	_GLIBCXX20_CONSTEXPR
5250	_OutputIterator
5251	__set_intersection(_InputIterator1 __first1, _InputIterator1 __last1,
5252	_InputIterator2 __first2, _InputIterator2 __last2,
5253	_OutputIterator __result, _Compare __comp)
5254	{
5255	while (__first1 != __last1 && __first2 != __last2)
5256	if (__comp(__first1, __first2))
5257	++__first1;
5258	else if (__comp(__first2, __first1))
5259	++__first2;
5260	else
5261	{
5262	__result = __first1;
5263	++__first1;
5264	++__first2;
5265	++__result;
5266	}
5267	return __result;
5268	}
5269
5270	/**
5271	* @brief Return the intersection of two sorted ranges.
5272	* @ingroup set_algorithms
5273	* @param __first1 Start of first range.
5274	* @param __last1 End of first range.
5275	* @param __first2 Start of second range.
5276	* @param __last2 End of second range.
5277	* @param __result Start of output range.
5278	* @return End of the output range.
5279	* @ingroup set_algorithms
5280	*
5281	* This operation iterates over both ranges, copying elements present in
5282	* both ranges in order to the output range. Iterators increment for each
5283	* range. When the current element of one range is less than the other,
5284	* that iterator advances. If an element is contained in both ranges, the
5285	* element from the first range is copied and both ranges advance. The
5286	* output range may not overlap either input range.
5287	*/
5288	template<typename _InputIterator1, typename _InputIterator2,
5289	typename _OutputIterator>
5290	_GLIBCXX20_CONSTEXPR
5291	inline _OutputIterator
5292	set_intersection(_InputIterator1 __first1, _InputIterator1 __last1,
5293	_InputIterator2 __first2, _InputIterator2 __last2,
5294	_OutputIterator __result)
5295	{
5296	// concept requirements
5297	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5298	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5299	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5300	typename iterator_traits<_InputIterator1>::value_type>)
5301	__glibcxx_function_requires(_LessThanOpConcept<
5302	typename iterator_traits<_InputIterator1>::value_type,
5303	typename iterator_traits<_InputIterator2>::value_type>)
5304	__glibcxx_function_requires(_LessThanOpConcept<
5305	typename iterator_traits<_InputIterator2>::value_type,
5306	typename iterator_traits<_InputIterator1>::value_type>)
5307	__glibcxx_requires_sorted_set(__first1, __last1, __first2);
5308	__glibcxx_requires_sorted_set(__first2, __last2, __first1);
5309	__glibcxx_requires_irreflexive2(__first1, __last1);
5310	__glibcxx_requires_irreflexive2(__first2, __last2);
5311
5312	return _GLIBCXX_STD_A::__set_intersection(__first1, __last1,
5313	__first2, __last2, __result,
5314	__gnu_cxx::__ops::__iter_less_iter());
5315	}
5316
5317	/**
5318	* @brief Return the intersection of two sorted ranges using comparison
5319	* functor.
5320	* @ingroup set_algorithms
5321	* @param __first1 Start of first range.
5322	* @param __last1 End of first range.
5323	* @param __first2 Start of second range.
5324	* @param __last2 End of second range.
5325	* @param __result Start of output range.
5326	* @param __comp The comparison functor.
5327	* @return End of the output range.
5328	* @ingroup set_algorithms
5329	*
5330	* This operation iterates over both ranges, copying elements present in
5331	* both ranges in order to the output range. Iterators increment for each
5332	* range. When the current element of one range is less than the other
5333	* according to @p __comp, that iterator advances. If an element is
5334	* contained in both ranges according to @p __comp, the element from the
5335	* first range is copied and both ranges advance. The output range may not
5336	* overlap either input range.
5337	*/
5338	template<typename _InputIterator1, typename _InputIterator2,
5339	typename _OutputIterator, typename _Compare>
5340	_GLIBCXX20_CONSTEXPR
5341	inline _OutputIterator
5342	set_intersection(_InputIterator1 __first1, _InputIterator1 __last1,
5343	_InputIterator2 __first2, _InputIterator2 __last2,
5344	_OutputIterator __result, _Compare __comp)
5345	{
5346	// concept requirements
5347	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5348	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5349	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5350	typename iterator_traits<_InputIterator1>::value_type>)
5351	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5352	typename iterator_traits<_InputIterator1>::value_type,
5353	typename iterator_traits<_InputIterator2>::value_type>)
5354	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5355	typename iterator_traits<_InputIterator2>::value_type,
5356	typename iterator_traits<_InputIterator1>::value_type>)
5357	__glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
5358	__glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);
5359	__glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
5360	__glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);
5361
5362	return _GLIBCXX_STD_A::__set_intersection(__first1, __last1,
5363	__first2, __last2, __result,
5364	__gnu_cxx::__ops::__iter_comp_iter(__comp));
5365	}
5366
5367	template<typename _InputIterator1, typename _InputIterator2,
5368	typename _OutputIterator,
5369	typename _Compare>
5370	_GLIBCXX20_CONSTEXPR
5371	_OutputIterator
5372	__set_difference(_InputIterator1 __first1, _InputIterator1 __last1,
5373	_InputIterator2 __first2, _InputIterator2 __last2,
5374	_OutputIterator __result, _Compare __comp)
5375	{
5376	while (__first1 != __last1 && __first2 != __last2)
5377	if (__comp(__first1, __first2))
5378	{
5379	__result = __first1;
5380	++__first1;
5381	++__result;
5382	}
5383	else if (__comp(__first2, __first1))
5384	++__first2;
5385	else
5386	{
5387	++__first1;
5388	++__first2;
5389	}
5390	return std::copy(__first1, __last1, __result);
5391	}
5392
5393	/**
5394	* @brief Return the difference of two sorted ranges.
5395	* @ingroup set_algorithms
5396	* @param __first1 Start of first range.
5397	* @param __last1 End of first range.
5398	* @param __first2 Start of second range.
5399	* @param __last2 End of second range.
5400	* @param __result Start of output range.
5401	* @return End of the output range.
5402	* @ingroup set_algorithms
5403	*
5404	* This operation iterates over both ranges, copying elements present in
5405	* the first range but not the second in order to the output range.
5406	* Iterators increment for each range. When the current element of the
5407	* first range is less than the second, that element is copied and the
5408	* iterator advances. If the current element of the second range is less,
5409	* the iterator advances, but no element is copied. If an element is
5410	* contained in both ranges, no elements are copied and both ranges
5411	* advance. The output range may not overlap either input range.
5412	*/
5413	template<typename _InputIterator1, typename _InputIterator2,
5414	typename _OutputIterator>
5415	_GLIBCXX20_CONSTEXPR
5416	inline _OutputIterator
5417	set_difference(_InputIterator1 __first1, _InputIterator1 __last1,
5418	_InputIterator2 __first2, _InputIterator2 __last2,
5419	_OutputIterator __result)
5420	{
5421	// concept requirements
5422	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5423	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5424	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5425	typename iterator_traits<_InputIterator1>::value_type>)
5426	__glibcxx_function_requires(_LessThanOpConcept<
5427	typename iterator_traits<_InputIterator1>::value_type,
5428	typename iterator_traits<_InputIterator2>::value_type>)
5429	__glibcxx_function_requires(_LessThanOpConcept<
5430	typename iterator_traits<_InputIterator2>::value_type,
5431	typename iterator_traits<_InputIterator1>::value_type>)
5432	__glibcxx_requires_sorted_set(__first1, __last1, __first2);
5433	__glibcxx_requires_sorted_set(__first2, __last2, __first1);
5434	__glibcxx_requires_irreflexive2(__first1, __last1);
5435	__glibcxx_requires_irreflexive2(__first2, __last2);
5436
5437	return _GLIBCXX_STD_A::__set_difference(__first1, __last1,
5438	__first2, __last2, __result,
5439	__gnu_cxx::__ops::__iter_less_iter());
5440	}
5441
5442	/**
5443	* @brief Return the difference of two sorted ranges using comparison
5444	* functor.
5445	* @ingroup set_algorithms
5446	* @param __first1 Start of first range.
5447	* @param __last1 End of first range.
5448	* @param __first2 Start of second range.
5449	* @param __last2 End of second range.
5450	* @param __result Start of output range.
5451	* @param __comp The comparison functor.
5452	* @return End of the output range.
5453	* @ingroup set_algorithms
5454	*
5455	* This operation iterates over both ranges, copying elements present in
5456	* the first range but not the second in order to the output range.
5457	* Iterators increment for each range. When the current element of the
5458	* first range is less than the second according to @p __comp, that element
5459	* is copied and the iterator advances. If the current element of the
5460	* second range is less, no element is copied and the iterator advances.
5461	* If an element is contained in both ranges according to @p __comp, no
5462	* elements are copied and both ranges advance. The output range may not
5463	* overlap either input range.
5464	*/
5465	template<typename _InputIterator1, typename _InputIterator2,
5466	typename _OutputIterator, typename _Compare>
5467	_GLIBCXX20_CONSTEXPR
5468	inline _OutputIterator
5469	set_difference(_InputIterator1 __first1, _InputIterator1 __last1,
5470	_InputIterator2 __first2, _InputIterator2 __last2,
5471	_OutputIterator __result, _Compare __comp)
5472	{
5473	// concept requirements
5474	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5475	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5476	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5477	typename iterator_traits<_InputIterator1>::value_type>)
5478	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5479	typename iterator_traits<_InputIterator1>::value_type,
5480	typename iterator_traits<_InputIterator2>::value_type>)
5481	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5482	typename iterator_traits<_InputIterator2>::value_type,
5483	typename iterator_traits<_InputIterator1>::value_type>)
5484	__glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
5485	__glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);
5486	__glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
5487	__glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);
5488
5489	return _GLIBCXX_STD_A::__set_difference(__first1, __last1,
5490	__first2, __last2, __result,
5491	__gnu_cxx::__ops::__iter_comp_iter(__comp));
5492	}
5493
5494	template<typename _InputIterator1, typename _InputIterator2,
5495	typename _OutputIterator,
5496	typename _Compare>
5497	_GLIBCXX20_CONSTEXPR
5498	_OutputIterator
5499	__set_symmetric_difference(_InputIterator1 __first1,
5500	_InputIterator1 __last1,
5501	_InputIterator2 __first2,
5502	_InputIterator2 __last2,
5503	_OutputIterator __result,
5504	_Compare __comp)
5505	{
5506	while (__first1 != __last1 && __first2 != __last2)
5507	if (__comp(__first1, __first2))
5508	{
5509	__result = __first1;
5510	++__first1;
5511	++__result;
5512	}
5513	else if (__comp(__first2, __first1))
5514	{
5515	__result = __first2;
5516	++__first2;
5517	++__result;
5518	}
5519	else
5520	{
5521	++__first1;
5522	++__first2;
5523	}
5524	return std::copy(__first2, __last2,
5525	std::copy(__first1, __last1, __result));
5526	}
5527
5528	/**
5529	* @brief Return the symmetric difference of two sorted ranges.
5530	* @ingroup set_algorithms
5531	* @param __first1 Start of first range.
5532	* @param __last1 End of first range.
5533	* @param __first2 Start of second range.
5534	* @param __last2 End of second range.
5535	* @param __result Start of output range.
5536	* @return End of the output range.
5537	* @ingroup set_algorithms
5538	*
5539	* This operation iterates over both ranges, copying elements present in
5540	* one range but not the other in order to the output range. Iterators
5541	* increment for each range. When the current element of one range is less
5542	* than the other, that element is copied and the iterator advances. If an
5543	* element is contained in both ranges, no elements are copied and both
5544	* ranges advance. The output range may not overlap either input range.
5545	*/
5546	template<typename _InputIterator1, typename _InputIterator2,
5547	typename _OutputIterator>
5548	_GLIBCXX20_CONSTEXPR
5549	inline _OutputIterator
5550	set_symmetric_difference(_InputIterator1 __first1, _InputIterator1 __last1,
5551	_InputIterator2 __first2, _InputIterator2 __last2,
5552	_OutputIterator __result)
5553	{
5554	// concept requirements
5555	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5556	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5557	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5558	typename iterator_traits<_InputIterator1>::value_type>)
5559	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5560	typename iterator_traits<_InputIterator2>::value_type>)
5561	__glibcxx_function_requires(_LessThanOpConcept<
5562	typename iterator_traits<_InputIterator1>::value_type,
5563	typename iterator_traits<_InputIterator2>::value_type>)
5564	__glibcxx_function_requires(_LessThanOpConcept<
5565	typename iterator_traits<_InputIterator2>::value_type,
5566	typename iterator_traits<_InputIterator1>::value_type>)
5567	__glibcxx_requires_sorted_set(__first1, __last1, __first2);
5568	__glibcxx_requires_sorted_set(__first2, __last2, __first1);
5569	__glibcxx_requires_irreflexive2(__first1, __last1);
5570	__glibcxx_requires_irreflexive2(__first2, __last2);
5571
5572	return _GLIBCXX_STD_A::__set_symmetric_difference(__first1, __last1,
5573	__first2, __last2, __result,
5574	__gnu_cxx::__ops::__iter_less_iter());
5575	}
5576
5577	/**
5578	* @brief Return the symmetric difference of two sorted ranges using
5579	* comparison functor.
5580	* @ingroup set_algorithms
5581	* @param __first1 Start of first range.
5582	* @param __last1 End of first range.
5583	* @param __first2 Start of second range.
5584	* @param __last2 End of second range.
5585	* @param __result Start of output range.
5586	* @param __comp The comparison functor.
5587	* @return End of the output range.
5588	* @ingroup set_algorithms
5589	*
5590	* This operation iterates over both ranges, copying elements present in
5591	* one range but not the other in order to the output range. Iterators
5592	* increment for each range. When the current element of one range is less
5593	* than the other according to @p comp, that element is copied and the
5594	* iterator advances. If an element is contained in both ranges according
5595	* to @p __comp, no elements are copied and both ranges advance. The output
5596	* range may not overlap either input range.
5597	*/
5598	template<typename _InputIterator1, typename _InputIterator2,
5599	typename _OutputIterator, typename _Compare>
5600	_GLIBCXX20_CONSTEXPR
5601	inline _OutputIterator
5602	set_symmetric_difference(_InputIterator1 __first1, _InputIterator1 __last1,
5603	_InputIterator2 __first2, _InputIterator2 __last2,
5604	_OutputIterator __result,
5605	_Compare __comp)
5606	{
5607	// concept requirements
5608	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5609	__glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5610	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5611	typename iterator_traits<_InputIterator1>::value_type>)
5612	__glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5613	typename iterator_traits<_InputIterator2>::value_type>)
5614	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5615	typename iterator_traits<_InputIterator1>::value_type,
5616	typename iterator_traits<_InputIterator2>::value_type>)
5617	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5618	typename iterator_traits<_InputIterator2>::value_type,
5619	typename iterator_traits<_InputIterator1>::value_type>)
5620	__glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
5621	__glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);
5622	__glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
5623	__glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);
5624
5625	return _GLIBCXX_STD_A::__set_symmetric_difference(__first1, __last1,
5626	__first2, __last2, __result,
5627	__gnu_cxx::__ops::__iter_comp_iter(__comp));
5628	}
5629
5630	template<typename _ForwardIterator, typename _Compare>
5631	_GLIBCXX14_CONSTEXPR
5632	_ForwardIterator
5633	__min_element(_ForwardIterator __first, _ForwardIterator __last,
5634	_Compare __comp)
5635	{
5636	if (__first == __last)
5637	return __first;
5638	_ForwardIterator __result = __first;
5639	while (++__first != __last)
5640	if (__comp(__first, __result))
5641	__result = __first;
5642	return __result;
5643	}
5644
5645	/**
5646	* @brief Return the minimum element in a range.
5647	* @ingroup sorting_algorithms
5648	* @param __first Start of range.
5649	* @param __last End of range.
5650	* @return Iterator referencing the first instance of the smallest value.
5651	*/
5652	template<typename _ForwardIterator>
5653	_GLIBCXX_NODISCARD _GLIBCXX14_CONSTEXPR
5654	_ForwardIterator
5655	inline min_element(_ForwardIterator __first, _ForwardIterator __last)
5656	{
5657	// concept requirements
5658	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
5659	__glibcxx_function_requires(_LessThanComparableConcept<
5660	typename iterator_traits<_ForwardIterator>::value_type>)
5661	__glibcxx_requires_valid_range(__first, __last);
5662	__glibcxx_requires_irreflexive(__first, __last);
5663
5664	return _GLIBCXX_STD_A::__min_element(__first, __last,
5665	__gnu_cxx::__ops::__iter_less_iter());
5666	}
5667
5668	/**
5669	* @brief Return the minimum element in a range using comparison functor.
5670	* @ingroup sorting_algorithms
5671	* @param __first Start of range.
5672	* @param __last End of range.
5673	* @param __comp Comparison functor.
5674	* @return Iterator referencing the first instance of the smallest value
5675	* according to __comp.
5676	*/
5677	template<typename _ForwardIterator, typename _Compare>
5678	_GLIBCXX_NODISCARD _GLIBCXX14_CONSTEXPR
5679	inline _ForwardIterator
5680	min_element(_ForwardIterator __first, _ForwardIterator __last,
5681	_Compare __comp)
5682	{
5683	// concept requirements
5684	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
5685	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5686	typename iterator_traits<_ForwardIterator>::value_type,
5687	typename iterator_traits<_ForwardIterator>::value_type>)
5688	__glibcxx_requires_valid_range(__first, __last);
5689	__glibcxx_requires_irreflexive_pred(__first, __last, __comp);
5690
5691	return _GLIBCXX_STD_A::__min_element(__first, __last,
5692	__gnu_cxx::__ops::__iter_comp_iter(__comp));
5693	}
5694
5695	template<typename _ForwardIterator, typename _Compare>
5696	_GLIBCXX14_CONSTEXPR
5697	_ForwardIterator
5698	__max_element(_ForwardIterator __first, _ForwardIterator __last,
5699	_Compare __comp)
5700	{
5701	if (__first == __last) return __first;
5702	_ForwardIterator __result = __first;
5703	while (++__first != __last)
5704	if (__comp(__result, __first))
5705	__result = __first;
5706	return __result;
5707	}
5708
5709	/**
5710	* @brief Return the maximum element in a range.
5711	* @ingroup sorting_algorithms
5712	* @param __first Start of range.
5713	* @param __last End of range.
5714	* @return Iterator referencing the first instance of the largest value.
5715	*/
5716	template<typename _ForwardIterator>
5717	_GLIBCXX_NODISCARD _GLIBCXX14_CONSTEXPR
5718	inline _ForwardIterator
5719	max_element(_ForwardIterator __first, _ForwardIterator __last)
5720	{
5721	// concept requirements
5722	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
5723	__glibcxx_function_requires(_LessThanComparableConcept<
5724	typename iterator_traits<_ForwardIterator>::value_type>)
5725	__glibcxx_requires_valid_range(__first, __last);
5726	__glibcxx_requires_irreflexive(__first, __last);
5727
5728	return _GLIBCXX_STD_A::__max_element(__first, __last,
5729	__gnu_cxx::__ops::__iter_less_iter());
5730	}
5731
5732	/**
5733	* @brief Return the maximum element in a range using comparison functor.
5734	* @ingroup sorting_algorithms
5735	* @param __first Start of range.
5736	* @param __last End of range.
5737	* @param __comp Comparison functor.
5738	* @return Iterator referencing the first instance of the largest value
5739	* according to __comp.
5740	*/
5741	template<typename _ForwardIterator, typename _Compare>
5742	_GLIBCXX_NODISCARD _GLIBCXX14_CONSTEXPR
5743	inline _ForwardIterator
5744	max_element(_ForwardIterator __first, _ForwardIterator __last,
5745	_Compare __comp)
5746	{
5747	// concept requirements
5748	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
5749	__glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5750	typename iterator_traits<_ForwardIterator>::value_type,
5751	typename iterator_traits<_ForwardIterator>::value_type>)
5752	__glibcxx_requires_valid_range(__first, __last);
5753	__glibcxx_requires_irreflexive_pred(__first, __last, __comp);
5754
5755	return _GLIBCXX_STD_A::__max_element(__first, __last,
5756	__gnu_cxx::__ops::__iter_comp_iter(__comp));
5757	}
5758
5759	#if __cplusplus >= 201103L
5760	// N2722 + DR 915.
5761	template<typename _Tp>
5762	_GLIBCXX14_CONSTEXPR
5763	inline _Tp
5764	min(initializer_list<_Tp> __l)
5765	{
5766	__glibcxx_requires_irreflexive(__l.begin(), __l.end());
5767	return *_GLIBCXX_STD_A::__min_element(__l.begin(), __l.end(),
5768	__gnu_cxx::__ops::__iter_less_iter());
5769	}
5770
5771	template<typename _Tp, typename _Compare>
5772	_GLIBCXX14_CONSTEXPR
5773	inline _Tp
5774	min(initializer_list<_Tp> __l, _Compare __comp)
5775	{
5776	__glibcxx_requires_irreflexive_pred(__l.begin(), __l.end(), __comp);
5777	return *_GLIBCXX_STD_A::__min_element(__l.begin(), __l.end(),
5778	__gnu_cxx::__ops::__iter_comp_iter(__comp));
5779	}
5780
5781	template<typename _Tp>
5782	_GLIBCXX14_CONSTEXPR
5783	inline _Tp
5784	max(initializer_list<_Tp> __l)
5785	{
5786	__glibcxx_requires_irreflexive(__l.begin(), __l.end());
5787	return *_GLIBCXX_STD_A::__max_element(__l.begin(), __l.end(),
5788	__gnu_cxx::__ops::__iter_less_iter());
5789	}
5790
5791	template<typename _Tp, typename _Compare>
5792	_GLIBCXX14_CONSTEXPR
5793	inline _Tp
5794	max(initializer_list<_Tp> __l, _Compare __comp)
5795	{
5796	__glibcxx_requires_irreflexive_pred(__l.begin(), __l.end(), __comp);
5797	return *_GLIBCXX_STD_A::__max_element(__l.begin(), __l.end(),
5798	__gnu_cxx::__ops::__iter_comp_iter(__comp));
5799	}
5800	#endif // C++11
5801
5802	#if __cplusplus >= 201402L
5803	/// Reservoir sampling algorithm.
5804	template<typename _InputIterator, typename _RandomAccessIterator,
5805	typename _Size, typename _UniformRandomBitGenerator>
5806	_RandomAccessIterator
5807	__sample(_InputIterator __first, _InputIterator __last, input_iterator_tag,
5808	_RandomAccessIterator __out, random_access_iterator_tag,
5809	_Size __n, _UniformRandomBitGenerator&& __g)
5810	{
5811	using __distrib_type = uniform_int_distribution<_Size>;
5812	using __param_type = typename __distrib_type::param_type;
5813	__distrib_type __d{};
5814	_Size __sample_sz = `0`;
5815	while (__first != __last && __sample_sz != __n)
5816	{
5817	__out[__sample_sz++] = *__first;
5818	++__first;
5819	}
5820	for (auto __pop_sz = __sample_sz; __first != __last;
5821	++__first, (void) ++__pop_sz)
5822	{
5823	const auto __k = __d(__g, __param_type{`0`, __pop_sz});
5824	if (__k < __n)
5825	__out[__k] = *__first;
5826	}
5827	return __out + __sample_sz;
5828	}
5829
5830	/// Selection sampling algorithm.
5831	template<typename _ForwardIterator, typename _OutputIterator, typename _Cat,
5832	typename _Size, typename _UniformRandomBitGenerator>
5833	_OutputIterator
5834	__sample(_ForwardIterator __first, _ForwardIterator __last,
5835	forward_iterator_tag,
5836	_OutputIterator __out, _Cat,
5837	_Size __n, _UniformRandomBitGenerator&& __g)
5838	{
5839	using __distrib_type = uniform_int_distribution<_Size>;
5840	using __param_type = typename __distrib_type::param_type;
5841	using _USize = make_unsigned_t<_Size>;
5842	using _Gen = remove_reference_t<_UniformRandomBitGenerator>;
5843	using __uc_type = common_type_t<typename _Gen::result_type, _USize>;
5844
5845	if (__first == __last)
5846	return __out;
5847
5848	__distrib_type __d{};
5849	_Size __unsampled_sz = std::distance(__first, __last);
5850	__n = std::min(__n, __unsampled_sz);
5851
5852	// If possible, we use __gen_two_uniform_ints to efficiently produce
5853	// two random numbers using a single distribution invocation:
5854
5855	const __uc_type __urngrange = __g.max() - __g.min();
5856	if (__urngrange / __uc_type(__unsampled_sz) >= __uc_type(__unsampled_sz))
5857	// I.e. (__urngrange >= __unsampled_sz __unsampled_sz) but without*
5858	// wrapping issues.
5859	{
5860	while (__n != `0` && __unsampled_sz >= `2`)
5861	{
5862	const pair<_Size, _Size> __p =
5863	__gen_two_uniform_ints(__unsampled_sz, __unsampled_sz - `1`, __g);
5864
5865	--__unsampled_sz;
5866	if (__p.first < __n)
5867	{
5868	__out++ = __first;
5869	--__n;
5870	}
5871
5872	++__first;
5873
5874	if (__n == `0`) break;
5875
5876	--__unsampled_sz;
5877	if (__p.second < __n)
5878	{
5879	__out++ = __first;
5880	--__n;
5881	}
5882
5883	++__first;
5884	}
5885	}
5886
5887	// The loop above is otherwise equivalent to this one-at-a-time version:
5888
5889	for (; __n != `0`; ++__first)
5890	if (__d(__g, __param_type{`0`, --__unsampled_sz}) < __n)
5891	{
5892	__out++ = __first;
5893	--__n;
5894	}
5895	return __out;
5896	}
5897	#endif // C++14
5898
5899	#ifdef __glibcxx_sample // C++ >= 17
5900	/// Take a random sample from a population.
5901	template<typename _PopulationIterator, typename _SampleIterator,
5902	typename _Distance, typename _UniformRandomBitGenerator>
5903	_SampleIterator
5904	sample(_PopulationIterator __first, _PopulationIterator __last,
5905	_SampleIterator __out, _Distance __n,
5906	_UniformRandomBitGenerator&& __g)
5907	{
5908	using __pop_cat = typename
5909	std::iterator_traits<_PopulationIterator>::iterator_category;
5910	using __samp_cat = typename
5911	std::iterator_traits<_SampleIterator>::iterator_category;
5912
5913	static_assert(
5914	__or_<is_convertible<__pop_cat, forward_iterator_tag>,
5915	is_convertible<__samp_cat, random_access_iterator_tag>>::value,
5916	"output range must use a RandomAccessIterator when input range"
5917	" does not meet the ForwardIterator requirements");
5918
5919	static_assert(is_integral<_Distance>::value,
5920	"sample size must be an integer type");
5921
5922	typename iterator_traits<_PopulationIterator>::difference_type __d = __n;
5923	return _GLIBCXX_STD_A::
5924	__sample(__first, __last, __pop_cat{}, __out, __samp_cat{}, __d,
5925	std::forward<_UniformRandomBitGenerator>(__g));
5926	}
5927	#endif // __glibcxx_sample
5928
5929	_GLIBCXX_END_NAMESPACE_ALGO
5930	_GLIBCXX_END_NAMESPACE_VERSION
5931	} // namespace std
5932
5933	#pragma GCC diagnostic pop
5934
5935	#endif /* _STL_ALGO_H */
5936

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