chrono source code [include/c++/14.1.1/chrono]

1	// <chrono> -- C++ --
2
3	// Copyright (C) 2008-2024 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	/* @file include/chrono*
26	* This is a Standard C++ Library header.
27	* @ingroup chrono
28	*/
29
30	#ifndef _GLIBCXX_CHRONO
31	#define _GLIBCXX_CHRONO 1
32
33	#pragma GCC system_header
34
35	#include <bits/requires_hosted.h> // for <ctime> and clocks
36
37	#if __cplusplus < 201103L
38	# include <bits/c++0x_warning.h>
39	#else
40
41	#include <bits/chrono.h>
42
43	#if __cplusplus >= 202002L
44	# include <bit>
45	# include <sstream>
46	# include <string>
47	# include <vector>
48	# include <bits/stl_algo.h> // upper_bound
49	# include <bits/shared_ptr.h>
50	# include <bits/unique_ptr.h>
51	#endif
52
53	#define __glibcxx_want_chrono
54	#define __glibcxx_want_chrono_udls
55	#include <bits/version.h>
56
57	namespace std _GLIBCXX_VISIBILITY(default)
58	{
59	_GLIBCXX_BEGIN_NAMESPACE_VERSION
60
61	/**
62	* @defgroup chrono Time
63	* @ingroup utilities
64	*
65	* Classes and functions for time.
66	*
67	* @since C++11
68	*/
69
70	/* @namespace std::chrono*
71	* @brief ISO C++ 2011 namespace for date and time utilities
72	* @ingroup chrono
73	*/
74	namespace chrono
75	{
76	#if __cplusplus >= 202002L
77	/// @addtogroup chrono
78	/// @{
79	struct local_t { };
80	template<typename _Duration>
81	using local_time = time_point<local_t, _Duration>;
82	using local_seconds = local_time<seconds>;
83	using local_days = local_time<days>;
84
85	class utc_clock;
86	class tai_clock;
87	class gps_clock;
88
89	template<typename _Duration>
90	using utc_time = time_point<utc_clock, _Duration>;
91	using utc_seconds = utc_time<seconds>;
92
93	template<typename _Duration>
94	using tai_time = time_point<tai_clock, _Duration>;
95	using tai_seconds = tai_time<seconds>;
96
97	template<typename _Duration>
98	using gps_time = time_point<gps_clock, _Duration>;
99	using gps_seconds = gps_time<seconds>;
100
101	template<> struct is_clock<utc_clock> : true_type { };
102	template<> struct is_clock<tai_clock> : true_type { };
103	template<> struct is_clock<gps_clock> : true_type { };
104
105	template<> inline constexpr bool is_clock_v<utc_clock> = true;
106	template<> inline constexpr bool is_clock_v<tai_clock> = true;
107	template<> inline constexpr bool is_clock_v<gps_clock> = true;
108
109	struct leap_second_info
110	{
111	bool is_leap_second;
112	seconds elapsed;
113	};
114
115	template<typename _Duration>
116	leap_second_info
117	get_leap_second_info(const utc_time<_Duration>& __ut);
118
119	/* A clock that measures Universal Coordinated Time (UTC).*
120	*
121	* The epoch is 1970-01-01 00:00:00.
122	*
123	* @since C++20
124	*/
125	class utc_clock
126	{
127	public:
128	using rep = system_clock::rep;
129	using period = system_clock::period;
130	using duration = chrono::duration<rep, period>;
131	using time_point = chrono::time_point<utc_clock>;
132	static constexpr bool is_steady = false;
133
134	[[nodiscard]]
135	static time_point
136	now()
137	{ return from_sys(system_clock::now()); }
138
139	template<typename _Duration>
140	[[nodiscard]]
141	static sys_time<common_type_t<_Duration, seconds>>
142	to_sys(const utc_time<_Duration>& __t)
143	{
144	using _CDur = common_type_t<_Duration, seconds>;
145	const auto __li = chrono::get_leap_second_info(__t);
146	sys_time<_CDur> __s{__t.time_since_epoch() - __li.elapsed};
147	if (__li.is_leap_second)
148	__s = chrono::floor<seconds>(__s) + seconds{`1`} - _CDur{`1`};
149	return __s;
150	}
151
152	template<typename _Duration>
153	[[nodiscard]]
154	static utc_time<common_type_t<_Duration, seconds>>
155	from_sys(const sys_time<_Duration>& __t);
156	};
157
158	/* A clock that measures International Atomic Time.*
159	*
160	* The epoch is 1958-01-01 00:00:00.
161	*
162	* @since C++20
163	*/
164	class tai_clock
165	{
166	public:
167	using rep = system_clock::rep;
168	using period = system_clock::period;
169	using duration = chrono::duration<rep, period>;
170	using time_point = chrono::time_point<tai_clock>;
171	static constexpr bool is_steady = false; // XXX true for CLOCK_TAI?
172
173	// TODO move into lib, use CLOCK_TAI on linux, add extension point.
174	[[nodiscard]]
175	static time_point
176	now()
177	{ return from_utc(utc_clock::now()); }
178
179	template<typename _Duration>
180	[[nodiscard]]
181	static utc_time<common_type_t<_Duration, seconds>>
182	to_utc(const tai_time<_Duration>& __t)
183	{
184	using _CDur = common_type_t<_Duration, seconds>;
185	return utc_time<_CDur>{__t.time_since_epoch()} - `378691210s`;
186	}
187
188	template<typename _Duration>
189	[[nodiscard]]
190	static tai_time<common_type_t<_Duration, seconds>>
191	from_utc(const utc_time<_Duration>& __t)
192	{
193	using _CDur = common_type_t<_Duration, seconds>;
194	return tai_time<_CDur>{__t.time_since_epoch()} + `378691210s`;
195	}
196	};
197
198	/* A clock that measures GPS time.*
199	*
200	* The epoch is 1980-01-06 00:00:00.
201	*
202	* @since C++20
203	*/
204	class gps_clock
205	{
206	public:
207	using rep = system_clock::rep;
208	using period = system_clock::period;
209	using duration = chrono::duration<rep, period>;
210	using time_point = chrono::time_point<gps_clock>;
211	static constexpr bool is_steady = false; // XXX
212
213	// TODO move into lib, add extension point.
214	[[nodiscard]]
215	static time_point
216	now()
217	{ return from_utc(utc_clock::now()); }
218
219	template<typename _Duration>
220	[[nodiscard]]
221	static utc_time<common_type_t<_Duration, seconds>>
222	to_utc(const gps_time<_Duration>& __t)
223	{
224	using _CDur = common_type_t<_Duration, seconds>;
225	return utc_time<_CDur>{__t.time_since_epoch()} + `315964809s`;
226	}
227
228	template<typename _Duration>
229	[[nodiscard]]
230	static gps_time<common_type_t<_Duration, seconds>>
231	from_utc(const utc_time<_Duration>& __t)
232	{
233	using _CDur = common_type_t<_Duration, seconds>;
234	return gps_time<_CDur>{__t.time_since_epoch()} - `315964809s`;
235	}
236	};
237
238
239	template<typename _DestClock, typename _SourceClock>
240	struct clock_time_conversion
241	{ };
242
243	// Identity conversions
244
245	template<typename _Clock>
246	struct clock_time_conversion<_Clock, _Clock>
247	{
248	template<typename _Duration>
249	time_point<_Clock, _Duration>
250	operator()(const time_point<_Clock, _Duration>& __t) const
251	{ return __t; }
252	};
253
254	template<>
255	struct clock_time_conversion<system_clock, system_clock>
256	{
257	template<typename _Duration>
258	sys_time<_Duration>
259	operator()(const sys_time<_Duration>& __t) const
260	{ return __t; }
261	};
262
263	template<>
264	struct clock_time_conversion<utc_clock, utc_clock>
265	{
266	template<typename _Duration>
267	utc_time<_Duration>
268	operator()(const utc_time<_Duration>& __t) const
269	{ return __t; }
270	};
271
272	// Conversions between system_clock and utc_clock
273
274	template<>
275	struct clock_time_conversion<utc_clock, system_clock>
276	{
277	template<typename _Duration>
278	utc_time<common_type_t<_Duration, seconds>>
279	operator()(const sys_time<_Duration>& __t) const
280	{ return utc_clock::from_sys(__t); }
281	};
282
283	template<>
284	struct clock_time_conversion<system_clock, utc_clock>
285	{
286	template<typename _Duration>
287	sys_time<common_type_t<_Duration, seconds>>
288	operator()(const utc_time<_Duration>& __t) const
289	{ return utc_clock::to_sys(__t); }
290	};
291
292	template<typename _Tp, typename _Clock>
293	inline constexpr bool __is_time_point_for_v = false;
294
295	template<typename _Clock, typename _Duration>
296	inline constexpr bool
297	__is_time_point_for_v<time_point<_Clock, _Duration>, _Clock> = true;
298
299	// Conversions between system_clock and other clocks
300
301	template<typename _SourceClock>
302	struct clock_time_conversion<system_clock, _SourceClock>
303	{
304	template<typename _Duration, typename _Src = _SourceClock>
305	auto
306	operator()(const time_point<_SourceClock, _Duration>& __t) const
307	-> decltype(_Src::to_sys(__t))
308	{
309	using _Ret = decltype(_SourceClock::to_sys(__t));
310	static_assert(__is_time_point_for_v<_Ret, system_clock>);
311	return _SourceClock::to_sys(__t);
312	}
313	};
314
315	template<typename _DestClock>
316	struct clock_time_conversion<_DestClock, system_clock>
317	{
318	template<typename _Duration, typename _Dest = _DestClock>
319	auto
320	operator()(const sys_time<_Duration>& __t) const
321	-> decltype(_Dest::from_sys(__t))
322	{
323	using _Ret = decltype(_DestClock::from_sys(__t));
324	static_assert(__is_time_point_for_v<_Ret, _DestClock>);
325	return _DestClock::from_sys(__t);
326	}
327	};
328
329	// Conversions between utc_clock and other clocks
330
331	template<typename _SourceClock>
332	struct clock_time_conversion<utc_clock, _SourceClock>
333	{
334	template<typename _Duration, typename _Src = _SourceClock>
335	auto
336	operator()(const time_point<_SourceClock, _Duration>& __t) const
337	-> decltype(_Src::to_utc(__t))
338	{
339	using _Ret = decltype(_SourceClock::to_utc(__t));
340	static_assert(__is_time_point_for_v<_Ret, utc_clock>);
341	return _SourceClock::to_utc(__t);
342	}
343	};
344
345	template<typename _DestClock>
346	struct clock_time_conversion<_DestClock, utc_clock>
347	{
348	template<typename _Duration, typename _Dest = _DestClock>
349	auto
350	operator()(const utc_time<_Duration>& __t) const
351	-> decltype(_Dest::from_utc(__t))
352	{
353	using _Ret = decltype(_DestClock::from_utc(__t));
354	static_assert(__is_time_point_for_v<_Ret, _DestClock>);
355	return _DestClock::from_utc(__t);
356	}
357	};
358
359	/// @cond undocumented
360	namespace __detail
361	{
362	template<typename _DestClock, typename _SourceClock, typename _Duration>
363	concept __clock_convs
364	= requires (const time_point<_SourceClock, _Duration>& __t) {
365	clock_time_conversion<_DestClock, _SourceClock>{}(__t);
366	};
367
368	template<typename _DestClock, typename _SourceClock, typename _Duration>
369	concept __clock_convs_sys
370	= requires (const time_point<_SourceClock, _Duration>& __t) {
371	clock_time_conversion<_DestClock, system_clock>{}(
372	clock_time_conversion<system_clock, _SourceClock>{}(__t));
373	};
374
375	template<typename _DestClock, typename _SourceClock, typename _Duration>
376	concept __clock_convs_utc
377	= requires (const time_point<_SourceClock, _Duration>& __t) {
378	clock_time_conversion<_DestClock, utc_clock>{}(
379	clock_time_conversion<utc_clock, _SourceClock>{}(__t));
380	};
381
382	template<typename _DestClock, typename _SourceClock, typename _Duration>
383	concept __clock_convs_sys_utc
384	= requires (const time_point<_SourceClock, _Duration>& __t) {
385	clock_time_conversion<_DestClock, utc_clock>{}(
386	clock_time_conversion<utc_clock, system_clock>{}(
387	clock_time_conversion<system_clock, _SourceClock>{}(__t)));
388	};
389
390	template<typename _DestClock, typename _SourceClock, typename _Duration>
391	concept __clock_convs_utc_sys
392	= requires (const time_point<_SourceClock, _Duration>& __t) {
393	clock_time_conversion<_DestClock, system_clock>{}(
394	clock_time_conversion<system_clock, utc_clock>{}(
395	clock_time_conversion<utc_clock, _SourceClock>{}(__t)));
396	};
397
398	} // namespace __detail
399	/// @endcond
400
401	/// Convert a time point to a different clock.
402	template<typename _DestClock, typename _SourceClock, typename _Duration>
403	[[nodiscard]]
404	inline auto
405	clock_cast(const time_point<_SourceClock, _Duration>& __t)
406	requires __detail::__clock_convs<_DestClock, _SourceClock, _Duration>
407	\|\| __detail::__clock_convs_sys<_DestClock, _SourceClock, _Duration>
408	\|\| __detail::__clock_convs_utc<_DestClock, _SourceClock, _Duration>
409	\|\| __detail::__clock_convs_sys_utc<_DestClock, _SourceClock, _Duration>
410	\|\| __detail::__clock_convs_utc_sys<_DestClock, _SourceClock, _Duration>
411	{
412	constexpr bool __direct
413	= __detail::__clock_convs<_DestClock, _SourceClock, _Duration>;
414	if constexpr (__direct)
415	{
416	return clock_time_conversion<_DestClock, _SourceClock>{}(__t);
417	}
418	else
419	{
420	constexpr bool __convert_via_sys_clock
421	= __detail::__clock_convs_sys<_DestClock, _SourceClock, _Duration>;
422	constexpr bool __convert_via_utc_clock
423	= __detail::__clock_convs_utc<_DestClock, _SourceClock, _Duration>;
424	if constexpr (__convert_via_sys_clock)
425	{
426	static_assert(!__convert_via_utc_clock,
427	"clock_cast requires a unique best conversion, but "
428	"conversion is possible via system_clock and also via"
429	"utc_clock");
430	return clock_time_conversion<_DestClock, system_clock>{}(
431	clock_time_conversion<system_clock, _SourceClock>{}(__t));
432	}
433	else if constexpr (__convert_via_utc_clock)
434	{
435	return clock_time_conversion<_DestClock, utc_clock>{}(
436	clock_time_conversion<utc_clock, _SourceClock>{}(__t));
437	}
438	else
439	{
440	constexpr bool __convert_via_sys_and_utc_clocks
441	= __detail::__clock_convs_sys_utc<_DestClock,
442	_SourceClock,
443	_Duration>;
444
445	if constexpr (__convert_via_sys_and_utc_clocks)
446	{
447	constexpr bool __convert_via_utc_and_sys_clocks
448	= __detail::__clock_convs_utc_sys<_DestClock,
449	_SourceClock,
450	_Duration>;
451	static_assert(!__convert_via_utc_and_sys_clocks,
452	"clock_cast requires a unique best conversion, but "
453	"conversion is possible via system_clock followed by "
454	"utc_clock, and also via utc_clock followed by "
455	"system_clock");
456	return clock_time_conversion<_DestClock, utc_clock>{}(
457	clock_time_conversion<utc_clock, system_clock>{}(
458	clock_time_conversion<system_clock, _SourceClock>{}(__t)));
459	}
460	else
461	{
462	return clock_time_conversion<_DestClock, system_clock>{}(
463	clock_time_conversion<system_clock, utc_clock>{}(
464	clock_time_conversion<utc_clock, _SourceClock>{}(__t)));
465	}
466	}
467	}
468	}
469
470	// CALENDRICAL TYPES
471
472	// CLASS DECLARATIONS
473	class day;
474	class month;
475	class year;
476	class weekday;
477	class weekday_indexed;
478	class weekday_last;
479	class month_day;
480	class month_day_last;
481	class month_weekday;
482	class month_weekday_last;
483	class year_month;
484	class year_month_day;
485	class year_month_day_last;
486	class year_month_weekday;
487	class year_month_weekday_last;
488
489	struct last_spec
490	{
491	explicit last_spec() = default;
492
493	friend constexpr month_day_last
494	operator/(int __m, last_spec) noexcept;
495
496	friend constexpr month_day_last
497	operator/(last_spec, int __m) noexcept;
498	};
499
500	inline constexpr last_spec last{};
501
502	namespace __detail
503	{
504	// Helper to __add_modulo and __sub_modulo.
505	template <unsigned __d, typename _Tp>
506	consteval auto
507	__modulo_offset()
508	{
509	using _Up = make_unsigned_t<_Tp>;
510	auto constexpr __a = _Up(-`1`) - _Up(`255` + __d - `2`);
511	auto constexpr __b = _Up(__d * (__a / __d) - `1`);
512	// Notice: b <= a - 1 <= _Up(-1) - (255 + d - 1) and b % d = d - 1.
513	return _Up(-`1`) - __b; // >= 255 + d - 1
514	}
515
516	// Compute the remainder of the Euclidean division of __x + __y divided by
517	// __d without overflowing. Typically, __x <= 255 + d - 1 is sum of
518	// weekday/month with a shift in [0, d - 1] and __y is a duration count.
519	template <unsigned __d, typename _Tp>
520	constexpr unsigned
521	__add_modulo(unsigned __x, _Tp __y)
522	{
523	using _Up = make_unsigned_t<_Tp>;
524	// For __y >= 0, _Up(__y) has the same mathematical value as __y and
525	// this function simply returns (__x + _Up(__y)) % d. Typically, this
526	// doesn't overflow since the range of _Up contains many more positive
527	// values than _Tp's. For __y < 0, _Up(__y) has a mathematical value in
528	// the upper-half range of _Up so that adding a positive value to it
529	// might overflow. Moreover, most likely, _Up(__y) != __y mod d. To
530	// fix both issues we subtract from _Up(__y) an __offset >=
531	// 255 + d - 1 to make room for the addition to __x and shift the modulo
532	// to the correct value.
533	auto const __offset = __y >= `0` ? _Up(`0`) : __modulo_offset<__d, _Tp>();
534	return (__x + _Up(__y) - __offset) % __d;
535	}
536
537	// Similar to __add_modulo but for __x - __y.
538	template <unsigned __d, typename _Tp>
539	constexpr unsigned
540	__sub_modulo(unsigned __x, _Tp __y)
541	{
542	using _Up = make_unsigned_t<_Tp>;
543	auto const __offset = __y <= `0` ? _Up(`0`) : __modulo_offset<__d, _Tp>();
544	return (__x - _Up(__y) - __offset) % __d;
545	}
546
547	inline constexpr unsigned __days_per_month[`12`]
548	= { `31`, `29`, `31`, `30`, `31`, `30`, `31`, `31`, `30`, `31`, `30`, `31` };
549	}
550
551	// DAY
552
553	class day
554	{
555	private:
556	unsigned char _M_d;
557
558	public:
559	day() = default;
560
561	explicit constexpr
562	day(unsigned __d) noexcept
563	: _M_d(__d)
564	{ }
565
566	constexpr day&
567	operator++() noexcept
568	{
569	++_M_d;
570	return *this;
571	}
572
573	constexpr day
574	operator++(int) noexcept
575	{
576	auto __ret = *this;
577	++(*this);
578	return __ret;
579	}
580
581	constexpr day&
582	operator--() noexcept
583	{
584	--_M_d;
585	return *this;
586	}
587
588	constexpr day
589	operator--(int) noexcept
590	{
591	auto __ret = *this;
592	--(*this);
593	return __ret;
594	}
595
596	constexpr day&
597	operator+=(const days& __d) noexcept
598	{
599	*this = *this + __d;
600	return *this;
601	}
602
603	constexpr day&
604	operator-=(const days& __d) noexcept
605	{
606	*this = *this - __d;
607	return *this;
608	}
609
610	constexpr explicit
611	operator unsigned() const noexcept
612	{ return _M_d; }
613
614	constexpr bool
615	ok() const noexcept
616	{ return `1` <= _M_d && _M_d <= `31`; }
617
618	friend constexpr bool
619	operator==(const day& __x, const day& __y) noexcept
620	{ return unsigned{__x} == unsigned{__y}; }
621
622	friend constexpr strong_ordering
623	operator<=>(const day& __x, const day& __y) noexcept
624	{ return unsigned{__x} <=> unsigned{__y}; }
625
626	friend constexpr day
627	operator+(const day& __x, const days& __y) noexcept
628	{ return day(unsigned{__x} + __y.count()); }
629
630	friend constexpr day
631	operator+(const days& __x, const day& __y) noexcept
632	{ return __y + __x; }
633
634	friend constexpr day
635	operator-(const day& __x, const days& __y) noexcept
636	{ return __x + -__y; }
637
638	friend constexpr days
639	operator-(const day& __x, const day& __y) noexcept
640	{ return days{int(unsigned{__x}) - int(unsigned{__y})}; }
641
642	friend constexpr month_day
643	operator/(const month& __m, const day& __d) noexcept;
644
645	friend constexpr month_day
646	operator/(int __m, const day& __d) noexcept;
647
648	friend constexpr month_day
649	operator/(const day& __d, const month& __m) noexcept;
650
651	friend constexpr month_day
652	operator/(const day& __d, int __m) noexcept;
653
654	friend constexpr year_month_day
655	operator/(const year_month& __ym, const day& __d) noexcept;
656	};
657
658	// MONTH
659
660	class month
661	{
662	private:
663	unsigned char _M_m;
664
665	public:
666	month() = default;
667
668	explicit constexpr
669	month(unsigned __m) noexcept
670	: _M_m(__m)
671	{ }
672
673	constexpr month&
674	operator++() noexcept
675	{
676	*this += months{`1`};
677	return *this;
678	}
679
680	constexpr month
681	operator++(int) noexcept
682	{
683	auto __ret = *this;
684	++(*this);
685	return __ret;
686	}
687
688	constexpr month&
689	operator--() noexcept
690	{
691	*this -= months{`1`};
692	return *this;
693	}
694
695	constexpr month
696	operator--(int) noexcept
697	{
698	auto __ret = *this;
699	--(*this);
700	return __ret;
701	}
702
703	constexpr month&
704	operator+=(const months& __m) noexcept
705	{
706	*this = *this + __m;
707	return *this;
708	}
709
710	constexpr month&
711	operator-=(const months& __m) noexcept
712	{
713	*this = *this - __m;
714	return *this;
715	}
716
717	explicit constexpr
718	operator unsigned() const noexcept
719	{ return _M_m; }
720
721	constexpr bool
722	ok() const noexcept
723	{ return `1` <= _M_m && _M_m <= `12`; }
724
725	friend constexpr bool
726	operator==(const month& __x, const month& __y) noexcept
727	{ return unsigned{__x} == unsigned{__y}; }
728
729	friend constexpr strong_ordering
730	operator<=>(const month& __x, const month& __y) noexcept
731	{ return unsigned{__x} <=> unsigned{__y}; }
732
733	friend constexpr month
734	operator+(const month& __x, const months& __y) noexcept
735	{
736	// modulo(x + (y - 1), 12) = modulo(x + (y - 1) + 12, 12)
737	// = modulo((x + 11) + y , 12)
738	return month{`1` + __detail::__add_modulo<`12`>(
739	unsigned{__x} + `11`, __y.count())};
740	}
741
742	friend constexpr month
743	operator+(const months& __x, const month& __y) noexcept
744	{ return __y + __x; }
745
746	friend constexpr month
747	operator-(const month& __x, const months& __y) noexcept
748	{
749	// modulo(x + (-y - 1), 12) = modulo(x + (-y - 1) + 12, 12)
750	// = modulo((x + 11) - y , 12)
751	return month{`1` + __detail::__sub_modulo<`12`>(
752	unsigned{__x} + `11`, __y.count())};
753	}
754
755	friend constexpr months
756	operator-(const month& __x, const month& __y) noexcept
757	{
758	const auto __dm = int(unsigned(__x)) - int(unsigned(__y));
759	return months{__dm < `0` ? `12` + __dm : __dm};
760	}
761
762	friend constexpr year_month
763	operator/(const year& __y, const month& __m) noexcept;
764
765	friend constexpr month_day
766	operator/(const month& __m, int __d) noexcept;
767
768	friend constexpr month_day_last
769	operator/(const month& __m, last_spec) noexcept;
770
771	friend constexpr month_day_last
772	operator/(last_spec, const month& __m) noexcept;
773
774	friend constexpr month_weekday
775	operator/(const month& __m, const weekday_indexed& __wdi) noexcept;
776
777	friend constexpr month_weekday
778	operator/(const weekday_indexed& __wdi, const month& __m) noexcept;
779
780	friend constexpr month_weekday_last
781	operator/(const month& __m, const weekday_last& __wdl) noexcept;
782
783	friend constexpr month_weekday_last
784	operator/(const weekday_last& __wdl, const month& __m) noexcept;
785	};
786
787	inline constexpr month January{`1`};
788	inline constexpr month February{`2`};
789	inline constexpr month March{`3`};
790	inline constexpr month April{`4`};
791	inline constexpr month May{`5`};
792	inline constexpr month June{`6`};
793	inline constexpr month July{`7`};
794	inline constexpr month August{`8`};
795	inline constexpr month September{`9`};
796	inline constexpr month October{`10`};
797	inline constexpr month November{`11`};
798	inline constexpr month December{`12`};
799
800	// YEAR
801
802	class year
803	{
804	private:
805	short _M_y;
806
807	public:
808	year() = default;
809
810	explicit constexpr
811	year(int __y) noexcept
812	: _M_y{static_cast<short>(__y)}
813	{ }
814
815	static constexpr year
816	min() noexcept
817	{ return year{-`32767`}; }
818
819	static constexpr year
820	max() noexcept
821	{ return year{`32767`}; }
822
823	constexpr year&
824	operator++() noexcept
825	{
826	++_M_y;
827	return *this;
828	}
829
830	constexpr year
831	operator++(int) noexcept
832	{
833	auto __ret = *this;
834	++(*this);
835	return __ret;
836	}
837
838	constexpr year&
839	operator--() noexcept
840	{
841	--_M_y;
842	return *this;
843	}
844
845	constexpr year
846	operator--(int) noexcept
847	{
848	auto __ret = *this;
849	--(*this);
850	return __ret;
851	}
852
853	constexpr year&
854	operator+=(const years& __y) noexcept
855	{
856	*this = *this + __y;
857	return *this;
858	}
859
860	constexpr year&
861	operator-=(const years& __y) noexcept
862	{
863	*this = *this - __y;
864	return *this;
865	}
866
867	constexpr year
868	operator+() const noexcept
869	{ return *this; }
870
871	constexpr year
872	operator-() const noexcept
873	{ return year{-_M_y}; }
874
875	constexpr bool
876	is_leap() const noexcept
877	{
878	// Testing divisibility by 100 first gives better performance [1], i.e.,
879	// return _M_y % 100 == 0 ? _M_y % 400 == 0 : _M_y % 16 == 0;
880	// Furthermore, if _M_y % 100 == 0, then _M_y % 400 == 0 is equivalent
881	// to _M_y % 16 == 0, so we can simplify it to
882	// return _M_y % 100 == 0 ? _M_y % 16 == 0 : _M_y % 4 == 0. // #1
883	// Similarly, we can replace 100 with 25 (which is good since
884	// _M_y % 25 == 0 requires one fewer instruction than _M_y % 100 == 0
885	// [2]):
886	// return _M_y % 25 == 0 ? _M_y % 16 == 0 : _M_y % 4 == 0. // #2
887	// Indeed, first assume _M_y % 4 != 0. Then _M_y % 16 != 0 and hence,
888	// _M_y % 4 == 0 and _M_y % 16 == 0 are both false. Therefore, #2
889	// returns false as it should (regardless of _M_y % 25.) Now assume
890	// _M_y % 4 == 0. In this case, _M_y % 25 == 0 if, and only if,
891	// _M_y % 100 == 0, that is, #1 and #2 are equivalent. Finally, #2 is
892	// equivalent to
893	// return (_M_y & (_M_y % 25 == 0 ? 15 : 3)) == 0.
894
895	// References:
896	// [1] https://github.com/cassioneri/calendar
897	// [2] https://godbolt.org/z/55G8rn77e
898	// [3] https://gcc.gnu.org/pipermail/libstdc++/2021-June/052815.html
899
900	return (_M_y & (_M_y % `25` == `0` ? `15` : `3`)) == `0`;
901	}
902
903	explicit constexpr
904	operator int() const noexcept
905	{ return _M_y; }
906
907	constexpr bool
908	ok() const noexcept
909	{ return min()._M_y <= _M_y && _M_y <= max()._M_y; }
910
911	friend constexpr bool
912	operator==(const year& __x, const year& __y) noexcept
913	{ return int{__x} == int{__y}; }
914
915	friend constexpr strong_ordering
916	operator<=>(const year& __x, const year& __y) noexcept
917	{ return int{__x} <=> int{__y}; }
918
919	friend constexpr year
920	operator+(const year& __x, const years& __y) noexcept
921	{ return year{int{__x} + static_cast<int>(__y.count())}; }
922
923	friend constexpr year
924	operator+(const years& __x, const year& __y) noexcept
925	{ return __y + __x; }
926
927	friend constexpr year
928	operator-(const year& __x, const years& __y) noexcept
929	{ return __x + -__y; }
930
931	friend constexpr years
932	operator-(const year& __x, const year& __y) noexcept
933	{ return years{int{__x} - int{__y}}; }
934
935	friend constexpr year_month
936	operator/(const year& __y, int __m) noexcept;
937
938	friend constexpr year_month_day
939	operator/(const year& __y, const month_day& __md) noexcept;
940
941	friend constexpr year_month_day
942	operator/(const month_day& __md, const year& __y) noexcept;
943
944	friend constexpr year_month_day_last
945	operator/(const year& __y, const month_day_last& __mdl) noexcept;
946
947	friend constexpr year_month_day_last
948	operator/(const month_day_last& __mdl, const year& __y) noexcept;
949
950	friend constexpr year_month_weekday
951	operator/(const year& __y, const month_weekday& __mwd) noexcept;
952
953	friend constexpr year_month_weekday
954	operator/(const month_weekday& __mwd, const year& __y) noexcept;
955
956	friend constexpr year_month_weekday_last
957	operator/(const year& __y, const month_weekday_last& __mwdl) noexcept;
958
959	friend constexpr year_month_weekday_last
960	operator/(const month_weekday_last& __mwdl, const year& __y) noexcept;
961	};
962
963	// WEEKDAY
964
965	class weekday
966	{
967	private:
968	unsigned char _M_wd;
969
970	static constexpr weekday
971	_S_from_days(const days& __d)
972	{
973	return weekday{__detail::__add_modulo<`7`>(`4`, __d.count())};
974	}
975
976	public:
977	weekday() = default;
978
979	explicit constexpr
980	weekday(unsigned __wd) noexcept
981	: _M_wd(__wd == `7` ? `0` : __wd) // __wd % 7 ?
982	{ }
983
984	constexpr
985	weekday(const sys_days& __dp) noexcept
986	: weekday{_S_from_days(__dp.time_since_epoch())}
987	{ }
988
989	explicit constexpr
990	weekday(const local_days& __dp) noexcept
991	: weekday{sys_days{__dp.time_since_epoch()}}
992	{ }
993
994	constexpr weekday&
995	operator++() noexcept
996	{
997	*this += days{`1`};
998	return *this;
999	}
1000
1001	constexpr weekday
1002	operator++(int) noexcept
1003	{
1004	auto __ret = *this;
1005	++(*this);
1006	return __ret;
1007	}
1008
1009	constexpr weekday&
1010	operator--() noexcept
1011	{
1012	*this -= days{`1`};
1013	return *this;
1014	}
1015
1016	constexpr weekday
1017	operator--(int) noexcept
1018	{
1019	auto __ret = *this;
1020	--(*this);
1021	return __ret;
1022	}
1023
1024	constexpr weekday&
1025	operator+=(const days& __d) noexcept
1026	{
1027	*this = *this + __d;
1028	return *this;
1029	}
1030
1031	constexpr weekday&
1032	operator-=(const days& __d) noexcept
1033	{
1034	*this = *this - __d;
1035	return *this;
1036	}
1037
1038	constexpr unsigned
1039	c_encoding() const noexcept
1040	{ return _M_wd; }
1041
1042	constexpr unsigned
1043	iso_encoding() const noexcept
1044	{ return _M_wd == `0u` ? `7u` : _M_wd; }
1045
1046	constexpr bool
1047	ok() const noexcept
1048	{ return _M_wd <= `6`; }
1049
1050	constexpr weekday_indexed
1051	operator[](unsigned __index) const noexcept;
1052
1053	constexpr weekday_last
1054	operator[](last_spec) const noexcept;
1055
1056	friend constexpr bool
1057	operator==(const weekday& __x, const weekday& __y) noexcept
1058	{ return __x._M_wd == __y._M_wd; }
1059
1060	friend constexpr weekday
1061	operator+(const weekday& __x, const days& __y) noexcept
1062	{
1063	return weekday{__detail::__add_modulo<`7`>(__x._M_wd, __y.count())};
1064	}
1065
1066	friend constexpr weekday
1067	operator+(const days& __x, const weekday& __y) noexcept
1068	{ return __y + __x; }
1069
1070	friend constexpr weekday
1071	operator-(const weekday& __x, const days& __y) noexcept
1072	{
1073	return weekday{__detail::__sub_modulo<`7`>(__x._M_wd, __y.count())};
1074	}
1075
1076	friend constexpr days
1077	operator-(const weekday& __x, const weekday& __y) noexcept
1078	{
1079	const auto __n = __x.c_encoding() - __y.c_encoding();
1080	return static_cast<int>(__n) >= `0` ? days{__n} : days{__n + `7`};
1081	}
1082	};
1083
1084	inline constexpr weekday Sunday{`0`};
1085	inline constexpr weekday Monday{`1`};
1086	inline constexpr weekday Tuesday{`2`};
1087	inline constexpr weekday Wednesday{`3`};
1088	inline constexpr weekday Thursday{`4`};
1089	inline constexpr weekday Friday{`5`};
1090	inline constexpr weekday Saturday{`6`};
1091
1092	// WEEKDAY_INDEXED
1093
1094	class weekday_indexed
1095	{
1096	private:
1097	chrono::weekday _M_wd;
1098	unsigned char _M_index;
1099
1100	public:
1101	weekday_indexed() = default;
1102
1103	constexpr
1104	weekday_indexed(const chrono::weekday& __wd, unsigned __index) noexcept
1105	: _M_wd(__wd), _M_index(__index)
1106	{ }
1107
1108	constexpr chrono::weekday
1109	weekday() const noexcept
1110	{ return _M_wd; }
1111
1112	constexpr unsigned
1113	index() const noexcept
1114	{ return _M_index; };
1115
1116	constexpr bool
1117	ok() const noexcept
1118	{ return _M_wd.ok() && `1` <= _M_index && _M_index <= `5`; }
1119
1120	friend constexpr bool
1121	operator==(const weekday_indexed& __x, const weekday_indexed& __y) noexcept
1122	{ return __x.weekday() == __y.weekday() && __x.index() == __y.index(); }
1123
1124	friend constexpr month_weekday
1125	operator/(const month& __m, const weekday_indexed& __wdi) noexcept;
1126
1127	friend constexpr month_weekday
1128	operator/(int __m, const weekday_indexed& __wdi) noexcept;
1129
1130	friend constexpr month_weekday
1131	operator/(const weekday_indexed& __wdi, const month& __m) noexcept;
1132
1133	friend constexpr month_weekday
1134	operator/(const weekday_indexed& __wdi, int __m) noexcept;
1135
1136	friend constexpr year_month_weekday
1137	operator/(const year_month& __ym, const weekday_indexed& __wdi) noexcept;
1138	};
1139
1140	constexpr weekday_indexed
1141	weekday::operator[](unsigned __index) const noexcept
1142	{ return {*this, __index}; }
1143
1144	// WEEKDAY_LAST
1145
1146	class weekday_last
1147	{
1148	private:
1149	chrono::weekday _M_wd;
1150
1151	public:
1152	explicit constexpr
1153	weekday_last(const chrono::weekday& __wd) noexcept
1154	: _M_wd{__wd}
1155	{ }
1156
1157	constexpr chrono::weekday
1158	weekday() const noexcept
1159	{ return _M_wd; }
1160
1161	constexpr bool
1162	ok() const noexcept
1163	{ return _M_wd.ok(); }
1164
1165	friend constexpr bool
1166	operator==(const weekday_last& __x, const weekday_last& __y) noexcept
1167	{ return __x.weekday() == __y.weekday(); }
1168
1169	friend constexpr month_weekday_last
1170	operator/(int __m, const weekday_last& __wdl) noexcept;
1171
1172	friend constexpr month_weekday_last
1173	operator/(const weekday_last& __wdl, int __m) noexcept;
1174
1175	friend constexpr year_month_weekday_last
1176	operator/(const year_month& __ym, const weekday_last& __wdl) noexcept;
1177	};
1178
1179	constexpr weekday_last
1180	weekday::operator[](last_spec) const noexcept
1181	{ return weekday_last{*this}; }
1182
1183	// MONTH_DAY
1184
1185	class month_day
1186	{
1187	private:
1188	chrono::month _M_m;
1189	chrono::day _M_d;
1190
1191	public:
1192	month_day() = default;
1193
1194	constexpr
1195	month_day(const chrono::month& __m, const chrono::day& __d) noexcept
1196	: _M_m{__m}, _M_d{__d}
1197	{ }
1198
1199	constexpr chrono::month
1200	month() const noexcept
1201	{ return _M_m; }
1202
1203	constexpr chrono::day
1204	day() const noexcept
1205	{ return _M_d; }
1206
1207	constexpr bool
1208	ok() const noexcept
1209	{
1210	return _M_m.ok()
1211	&& `1u` <= unsigned(_M_d)
1212	&& unsigned(_M_d) <= __detail::__days_per_month[unsigned(_M_m) - `1`];
1213	}
1214
1215	friend constexpr bool
1216	operator==(const month_day& __x, const month_day& __y) noexcept
1217	{ return __x.month() == __y.month() && __x.day() == __y.day(); }
1218
1219	friend constexpr strong_ordering
1220	operator<=>(const month_day& __x, const month_day& __y) noexcept
1221	= default;
1222
1223	friend constexpr month_day
1224	operator/(const chrono::month& __m, const chrono::day& __d) noexcept
1225	{ return {__m, __d}; }
1226
1227	friend constexpr month_day
1228	operator/(const chrono::month& __m, int __d) noexcept
1229	{ return {__m, chrono::day(unsigned(__d))}; }
1230
1231	friend constexpr month_day
1232	operator/(int __m, const chrono::day& __d) noexcept
1233	{ return {chrono::month(unsigned(__m)), __d}; }
1234
1235	friend constexpr month_day
1236	operator/(const chrono::day& __d, const chrono::month& __m) noexcept
1237	{ return {__m, __d}; }
1238
1239	friend constexpr month_day
1240	operator/(const chrono::day& __d, int __m) noexcept
1241	{ return {chrono::month(unsigned(__m)), __d}; }
1242
1243	friend constexpr year_month_day
1244	operator/(int __y, const month_day& __md) noexcept;
1245
1246	friend constexpr year_month_day
1247	operator/(const month_day& __md, int __y) noexcept;
1248	};
1249
1250	// MONTH_DAY_LAST
1251
1252	class month_day_last
1253	{
1254	private:
1255	chrono::month _M_m;
1256
1257	public:
1258	explicit constexpr
1259	month_day_last(const chrono::month& __m) noexcept
1260	: _M_m{__m}
1261	{ }
1262
1263	constexpr chrono::month
1264	month() const noexcept
1265	{ return _M_m; }
1266
1267	constexpr bool
1268	ok() const noexcept
1269	{ return _M_m.ok(); }
1270
1271	friend constexpr bool
1272	operator==(const month_day_last& __x, const month_day_last& __y) noexcept
1273	{ return __x.month() == __y.month(); }
1274
1275	friend constexpr strong_ordering
1276	operator<=>(const month_day_last& __x, const month_day_last& __y) noexcept
1277	= default;
1278
1279	friend constexpr month_day_last
1280	operator/(const chrono::month& __m, last_spec) noexcept
1281	{ return month_day_last{__m}; }
1282
1283	friend constexpr month_day_last
1284	operator/(int __m, last_spec) noexcept
1285	{ return chrono::month(unsigned(__m)) / last; }
1286
1287	friend constexpr month_day_last
1288	operator/(last_spec, const chrono::month& __m) noexcept
1289	{ return __m / last; }
1290
1291	friend constexpr month_day_last
1292	operator/(last_spec, int __m) noexcept
1293	{ return __m / last; }
1294
1295	friend constexpr year_month_day_last
1296	operator/(int __y, const month_day_last& __mdl) noexcept;
1297
1298	friend constexpr year_month_day_last
1299	operator/(const month_day_last& __mdl, int __y) noexcept;
1300	};
1301
1302	// MONTH_WEEKDAY
1303
1304	class month_weekday
1305	{
1306	private:
1307	chrono::month _M_m;
1308	chrono::weekday_indexed _M_wdi;
1309
1310	public:
1311	constexpr
1312	month_weekday(const chrono::month& __m,
1313	const chrono::weekday_indexed& __wdi) noexcept
1314	: _M_m{__m}, _M_wdi{__wdi}
1315	{ }
1316
1317	constexpr chrono::month
1318	month() const noexcept
1319	{ return _M_m; }
1320
1321	constexpr chrono::weekday_indexed
1322	weekday_indexed() const noexcept
1323	{ return _M_wdi; }
1324
1325	constexpr bool
1326	ok() const noexcept
1327	{ return _M_m.ok() && _M_wdi.ok(); }
1328
1329	friend constexpr bool
1330	operator==(const month_weekday& __x, const month_weekday& __y) noexcept
1331	{
1332	return __x.month() == __y.month()
1333	&& __x.weekday_indexed() == __y.weekday_indexed();
1334	}
1335
1336	friend constexpr month_weekday
1337	operator/(const chrono::month& __m,
1338	const chrono::weekday_indexed& __wdi) noexcept
1339	{ return {__m, __wdi}; }
1340
1341	friend constexpr month_weekday
1342	operator/(int __m, const chrono::weekday_indexed& __wdi) noexcept
1343	{ return chrono::month(unsigned(__m)) / __wdi; }
1344
1345	friend constexpr month_weekday
1346	operator/(const chrono::weekday_indexed& __wdi,
1347	const chrono::month& __m) noexcept
1348	{ return __m / __wdi; }
1349
1350	friend constexpr month_weekday
1351	operator/(const chrono::weekday_indexed& __wdi, int __m) noexcept
1352	{ return __m / __wdi; }
1353
1354	friend constexpr year_month_weekday
1355	operator/(int __y, const month_weekday& __mwd) noexcept;
1356
1357	friend constexpr year_month_weekday
1358	operator/(const month_weekday& __mwd, int __y) noexcept;
1359	};
1360
1361	// MONTH_WEEKDAY_LAST
1362
1363	class month_weekday_last
1364	{
1365	private:
1366	chrono::month _M_m;
1367	chrono::weekday_last _M_wdl;
1368
1369	public:
1370	constexpr
1371	month_weekday_last(const chrono::month& __m,
1372	const chrono::weekday_last& __wdl) noexcept
1373	:_M_m{__m}, _M_wdl{__wdl}
1374	{ }
1375
1376	constexpr chrono::month
1377	month() const noexcept
1378	{ return _M_m; }
1379
1380	constexpr chrono::weekday_last
1381	weekday_last() const noexcept
1382	{ return _M_wdl; }
1383
1384	constexpr bool
1385	ok() const noexcept
1386	{ return _M_m.ok() && _M_wdl.ok(); }
1387
1388	friend constexpr bool
1389	operator==(const month_weekday_last& __x,
1390	const month_weekday_last& __y) noexcept
1391	{
1392	return __x.month() == __y.month()
1393	&& __x.weekday_last() == __y.weekday_last();
1394	}
1395
1396	friend constexpr month_weekday_last
1397	operator/(const chrono::month& __m,
1398	const chrono::weekday_last& __wdl) noexcept
1399	{ return {__m, __wdl}; }
1400
1401	friend constexpr month_weekday_last
1402	operator/(int __m, const chrono::weekday_last& __wdl) noexcept
1403	{ return chrono::month(unsigned(__m)) / __wdl; }
1404
1405	friend constexpr month_weekday_last
1406	operator/(const chrono::weekday_last& __wdl,
1407	const chrono::month& __m) noexcept
1408	{ return __m / __wdl; }
1409
1410	friend constexpr month_weekday_last
1411	operator/(const chrono::weekday_last& __wdl, int __m) noexcept
1412	{ return chrono::month(unsigned(__m)) / __wdl; }
1413
1414	friend constexpr year_month_weekday_last
1415	operator/(int __y, const month_weekday_last& __mwdl) noexcept;
1416
1417	friend constexpr year_month_weekday_last
1418	operator/(const month_weekday_last& __mwdl, int __y) noexcept;
1419	};
1420
1421	// YEAR_MONTH
1422
1423	namespace __detail
1424	{
1425	// [time.cal.ym], [time.cal.ymd], etc constrain the 'months'-based
1426	// addition/subtraction operator overloads like so:
1427	//
1428	// Constraints: if the argument supplied by the caller for the months
1429	// parameter is convertible to years, its implicit conversion sequence
1430	// to years is worse than its implicit conversion sequence to months.
1431	//
1432	// We realize this constraint by templatizing the 'months'-based
1433	// overloads (using a dummy defaulted template parameter), so that
1434	// overload resolution doesn't select the 'months'-based overload unless
1435	// the implicit conversion sequence to 'months' is better than that to
1436	// 'years'.
1437	using __months_years_conversion_disambiguator = void;
1438	}
1439
1440	class year_month
1441	{
1442	private:
1443	chrono::year _M_y;
1444	chrono::month _M_m;
1445
1446	public:
1447	year_month() = default;
1448
1449	constexpr
1450	year_month(const chrono::year& __y, const chrono::month& __m) noexcept
1451	: _M_y{__y}, _M_m{__m}
1452	{ }
1453
1454	constexpr chrono::year
1455	year() const noexcept
1456	{ return _M_y; }
1457
1458	constexpr chrono::month
1459	month() const noexcept
1460	{ return _M_m; }
1461
1462	template<typename = __detail::__months_years_conversion_disambiguator>
1463	constexpr year_month&
1464	operator+=(const months& __dm) noexcept
1465	{
1466	*this = *this + __dm;
1467	return *this;
1468	}
1469
1470	template<typename = __detail::__months_years_conversion_disambiguator>
1471	constexpr year_month&
1472	operator-=(const months& __dm) noexcept
1473	{
1474	*this = *this - __dm;
1475	return *this;
1476	}
1477
1478	constexpr year_month&
1479	operator+=(const years& __dy) noexcept
1480	{
1481	*this = *this + __dy;
1482	return *this;
1483	}
1484
1485	constexpr year_month&
1486	operator-=(const years& __dy) noexcept
1487	{
1488	*this = *this - __dy;
1489	return *this;
1490	}
1491
1492	constexpr bool
1493	ok() const noexcept
1494	{ return _M_y.ok() && _M_m.ok(); }
1495
1496	friend constexpr bool
1497	operator==(const year_month& __x, const year_month& __y) noexcept
1498	{ return __x.year() == __y.year() && __x.month() == __y.month(); }
1499
1500	friend constexpr strong_ordering
1501	operator<=>(const year_month& __x, const year_month& __y) noexcept
1502	= default;
1503
1504	template<typename = __detail::__months_years_conversion_disambiguator>
1505	friend constexpr year_month
1506	operator+(const year_month& __ym, const months& __dm) noexcept
1507	{
1508	// TODO: Optimize?
1509	auto __m = __ym.month() + __dm;
1510	auto __i = int(unsigned(__ym.month())) - `1` + __dm.count();
1511	auto __y = (__i < `0`
1512	? __ym.year() + years{(__i - `11`) / `12`}
1513	: __ym.year() + years{__i / `12`});
1514	return __y / __m;
1515	}
1516
1517	template<typename = __detail::__months_years_conversion_disambiguator>
1518	friend constexpr year_month
1519	operator+(const months& __dm, const year_month& __ym) noexcept
1520	{ return __ym + __dm; }
1521
1522	template<typename = __detail::__months_years_conversion_disambiguator>
1523	friend constexpr year_month
1524	operator-(const year_month& __ym, const months& __dm) noexcept
1525	{ return __ym + -__dm; }
1526
1527	friend constexpr months
1528	operator-(const year_month& __x, const year_month& __y) noexcept
1529	{
1530	return (__x.year() - __y.year()
1531	+ months{static_cast<int>(unsigned{__x.month()})
1532	- static_cast<int>(unsigned{__y.month()})});
1533	}
1534
1535	friend constexpr year_month
1536	operator+(const year_month& __ym, const years& __dy) noexcept
1537	{ return (__ym.year() + __dy) / __ym.month(); }
1538
1539	friend constexpr year_month
1540	operator+(const years& __dy, const year_month& __ym) noexcept
1541	{ return __ym + __dy; }
1542
1543	friend constexpr year_month
1544	operator-(const year_month& __ym, const years& __dy) noexcept
1545	{ return __ym + -__dy; }
1546
1547	friend constexpr year_month
1548	operator/(const chrono::year& __y, const chrono::month& __m) noexcept
1549	{ return {__y, __m}; }
1550
1551	friend constexpr year_month
1552	operator/(const chrono::year& __y, int __m) noexcept
1553	{ return {__y, chrono::month(unsigned(__m))}; }
1554
1555	friend constexpr year_month_day
1556	operator/(const year_month& __ym, int __d) noexcept;
1557
1558	friend constexpr year_month_day_last
1559	operator/(const year_month& __ym, last_spec) noexcept;
1560	};
1561
1562	// YEAR_MONTH_DAY
1563
1564	class year_month_day
1565	{
1566	private:
1567	chrono::year _M_y;
1568	chrono::month _M_m;
1569	chrono::day _M_d;
1570
1571	static constexpr year_month_day _S_from_days(const days& __dp) noexcept;
1572
1573	constexpr days _M_days_since_epoch() const noexcept;
1574
1575	public:
1576	year_month_day() = default;
1577
1578	constexpr
1579	year_month_day(const chrono::year& __y, const chrono::month& __m,
1580	const chrono::day& __d) noexcept
1581	: _M_y{__y}, _M_m{__m}, _M_d{__d}
1582	{ }
1583
1584	constexpr
1585	year_month_day(const year_month_day_last& __ymdl) noexcept;
1586
1587	constexpr
1588	year_month_day(const sys_days& __dp) noexcept
1589	: year_month_day(_S_from_days(__dp.time_since_epoch()))
1590	{ }
1591
1592	explicit constexpr
1593	year_month_day(const local_days& __dp) noexcept
1594	: year_month_day(sys_days{__dp.time_since_epoch()})
1595	{ }
1596
1597	template<typename = __detail::__months_years_conversion_disambiguator>
1598	constexpr year_month_day&
1599	operator+=(const months& __m) noexcept
1600	{
1601	*this = *this + __m;
1602	return *this;
1603	}
1604
1605	template<typename = __detail::__months_years_conversion_disambiguator>
1606	constexpr year_month_day&
1607	operator-=(const months& __m) noexcept
1608	{
1609	*this = *this - __m;
1610	return *this;
1611	}
1612
1613	constexpr year_month_day&
1614	operator+=(const years& __y) noexcept
1615	{
1616	*this = *this + __y;
1617	return *this;
1618	}
1619
1620	constexpr year_month_day&
1621	operator-=(const years& __y) noexcept
1622	{
1623	*this = *this - __y;
1624	return *this;
1625	}
1626
1627	constexpr chrono::year
1628	year() const noexcept
1629	{ return _M_y; }
1630
1631	constexpr chrono::month
1632	month() const noexcept
1633	{ return _M_m; }
1634
1635	constexpr chrono::day
1636	day() const noexcept
1637	{ return _M_d; }
1638
1639	constexpr
1640	operator sys_days() const noexcept
1641	{ return sys_days{_M_days_since_epoch()}; }
1642
1643	explicit constexpr
1644	operator local_days() const noexcept
1645	{ return local_days{sys_days{*this}.time_since_epoch()}; }
1646
1647	constexpr bool ok() const noexcept;
1648
1649	friend constexpr bool
1650	operator==(const year_month_day& __x, const year_month_day& __y) noexcept
1651	{
1652	return __x.year() == __y.year()
1653	&& __x.month() == __y.month()
1654	&& __x.day() == __y.day();
1655	}
1656
1657	friend constexpr strong_ordering
1658	operator<=>(const year_month_day& __x, const year_month_day& __y) noexcept
1659	= default;
1660
1661	template<typename = __detail::__months_years_conversion_disambiguator>
1662	friend constexpr year_month_day
1663	operator+(const year_month_day& __ymd, const months& __dm) noexcept
1664	{ return (__ymd.year() / __ymd.month() + __dm) / __ymd.day(); }
1665
1666	template<typename = __detail::__months_years_conversion_disambiguator>
1667	friend constexpr year_month_day
1668	operator+(const months& __dm, const year_month_day& __ymd) noexcept
1669	{ return __ymd + __dm; }
1670
1671	friend constexpr year_month_day
1672	operator+(const year_month_day& __ymd, const years& __dy) noexcept
1673	{ return (__ymd.year() + __dy) / __ymd.month() / __ymd.day(); }
1674
1675	friend constexpr year_month_day
1676	operator+(const years& __dy, const year_month_day& __ymd) noexcept
1677	{ return __ymd + __dy; }
1678
1679	template<typename = __detail::__months_years_conversion_disambiguator>
1680	friend constexpr year_month_day
1681	operator-(const year_month_day& __ymd, const months& __dm) noexcept
1682	{ return __ymd + -__dm; }
1683
1684	friend constexpr year_month_day
1685	operator-(const year_month_day& __ymd, const years& __dy) noexcept
1686	{ return __ymd + -__dy; }
1687
1688	friend constexpr year_month_day
1689	operator/(const year_month& __ym, const chrono::day& __d) noexcept
1690	{ return {__ym.year(), __ym.month(), __d}; }
1691
1692	friend constexpr year_month_day
1693	operator/(const year_month& __ym, int __d) noexcept
1694	{ return __ym / chrono::day{unsigned(__d)}; }
1695
1696	friend constexpr year_month_day
1697	operator/(const chrono::year& __y, const month_day& __md) noexcept
1698	{ return __y / __md.month() / __md.day(); }
1699
1700	friend constexpr year_month_day
1701	operator/(int __y, const month_day& __md) noexcept
1702	{ return chrono::year{__y} / __md; }
1703
1704	friend constexpr year_month_day
1705	operator/(const month_day& __md, const chrono::year& __y) noexcept
1706	{ return __y / __md; }
1707
1708	friend constexpr year_month_day
1709	operator/(const month_day& __md, int __y) noexcept
1710	{ return chrono::year(__y) / __md; }
1711	};
1712
1713	// Construct from days since 1970/01/01.
1714	// Proposition 6.3 of Neri and Schneider,
1715	// "Euclidean Affine Functions and Applications to Calendar Algorithms".
1716	// https://arxiv.org/abs/2102.06959
1717	constexpr year_month_day
1718	year_month_day::_S_from_days(const days& __dp) noexcept
1719	{
1720	constexpr auto __z2 = static_cast<uint32_t>(-`1468000`);
1721	constexpr auto __r2_e3 = static_cast<uint32_t>(`536895458`);
1722
1723	const auto __r0 = static_cast<uint32_t>(__dp.count()) + __r2_e3;
1724
1725	const auto __n1 = `4` * __r0 + `3`;
1726	const auto __q1 = __n1 / `146097`;
1727	const auto __r1 = __n1 % `146097` / `4`;
1728
1729	constexpr auto __p32 = static_cast<uint64_t>(`1`) << `32`;
1730	const auto __n2 = `4` * __r1 + `3`;
1731	const auto __u2 = static_cast<uint64_t>(`2939745`) * __n2;
1732	const auto __q2 = static_cast<uint32_t>(__u2 / __p32);
1733	const auto __r2 = static_cast<uint32_t>(__u2 % __p32) / `2939745` / `4`;
1734
1735	constexpr auto __p16 = static_cast<uint32_t>(`1`) << `16`;
1736	const auto __n3 = `2141` * __r2 + `197913`;
1737	const auto __q3 = __n3 / __p16;
1738	const auto __r3 = __n3 % __p16 / `2141`;
1739
1740	const auto __y0 = `100` * __q1 + __q2;
1741	const auto __m0 = __q3;
1742	const auto __d0 = __r3;
1743
1744	const auto __j = __r2 >= `306`;
1745	const auto __y1 = __y0 + __j;
1746	const auto __m1 = __j ? __m0 - `12` : __m0;
1747	const auto __d1 = __d0 + `1`;
1748
1749	return year_month_day{chrono::year{static_cast<int>(__y1 + __z2)},
1750	chrono::month{__m1}, chrono::day{__d1}};
1751	}
1752
1753	// Days since 1970/01/01.
1754	// Proposition 6.2 of Neri and Schneider,
1755	// "Euclidean Affine Functions and Applications to Calendar Algorithms".
1756	// https://arxiv.org/abs/2102.06959
1757	constexpr days
1758	year_month_day::_M_days_since_epoch() const noexcept
1759	{
1760	auto constexpr __z2 = static_cast<uint32_t>(-`1468000`);
1761	auto constexpr __r2_e3 = static_cast<uint32_t>(`536895458`);
1762
1763	const auto __y1 = static_cast<uint32_t>(static_cast<int>(_M_y)) - __z2;
1764	const auto __m1 = static_cast<uint32_t>(static_cast<unsigned>(_M_m));
1765	const auto __d1 = static_cast<uint32_t>(static_cast<unsigned>(_M_d));
1766
1767	const auto __j = static_cast<uint32_t>(__m1 < `3`);
1768	const auto __y0 = __y1 - __j;
1769	const auto __m0 = __j ? __m1 + `12` : __m1;
1770	const auto __d0 = __d1 - `1`;
1771
1772	const auto __q1 = __y0 / `100`;
1773	const auto __yc = `1461` * __y0 / `4` - __q1 + __q1 / `4`;
1774	const auto __mc = (`979` *__m0 - `2919`) / `32`;
1775	const auto __dc = __d0;
1776
1777	return days{static_cast<int32_t>(__yc + __mc + __dc - __r2_e3)};
1778	}
1779
1780	// YEAR_MONTH_DAY_LAST
1781
1782	class year_month_day_last
1783	{
1784	private:
1785	chrono::year _M_y;
1786	chrono::month_day_last _M_mdl;
1787
1788	public:
1789	constexpr
1790	year_month_day_last(const chrono::year& __y,
1791	const chrono::month_day_last& __mdl) noexcept
1792	: _M_y{__y}, _M_mdl{__mdl}
1793	{ }
1794
1795	template<typename = __detail::__months_years_conversion_disambiguator>
1796	constexpr year_month_day_last&
1797	operator+=(const months& __m) noexcept
1798	{
1799	*this = *this + __m;
1800	return *this;
1801	}
1802
1803	template<typename = __detail::__months_years_conversion_disambiguator>
1804	constexpr year_month_day_last&
1805	operator-=(const months& __m) noexcept
1806	{
1807	*this = *this - __m;
1808	return *this;
1809	}
1810
1811	constexpr year_month_day_last&
1812	operator+=(const years& __y) noexcept
1813	{
1814	*this = *this + __y;
1815	return *this;
1816	}
1817
1818	constexpr year_month_day_last&
1819	operator-=(const years& __y) noexcept
1820	{
1821	*this = *this - __y;
1822	return *this;
1823	}
1824
1825	constexpr chrono::year
1826	year() const noexcept
1827	{ return _M_y; }
1828
1829	constexpr chrono::month
1830	month() const noexcept
1831	{ return _M_mdl.month(); }
1832
1833	constexpr chrono::month_day_last
1834	month_day_last() const noexcept
1835	{ return _M_mdl; }
1836
1837	// Return A day representing the last day of this year, month pair.
1838	constexpr chrono::day
1839	day() const noexcept
1840	{
1841	const auto __m = static_cast<unsigned>(month());
1842
1843	// The result is unspecified if __m < 1 or __m > 12. Hence, assume
1844	// 1 <= __m <= 12. For __m != 2, day() == 30 or day() == 31 or, in
1845	// other words, day () == 30 \| b, where b is in {0, 1}.
1846
1847	// If __m in {1, 3, 4, 5, 6, 7}, then b is 1 if, and only if, __m is
1848	// odd. Hence, b = __m & 1 = (__m ^ 0) & 1.
1849
1850	// If __m in {8, 9, 10, 11, 12}, then b is 1 if, and only if, __m is
1851	// even. Hence, b = (__m ^ 1) & 1.
1852
1853	// Therefore, b = (__m ^ c) & 1, where c = 0, if __m < 8, or c = 1 if
1854	// __m >= 8, that is, c = __m >> 3.
1855
1856	// Since 30 = (11110)_2 and __m <= 31 = (11111)_2, the "& 1" in b's
1857	// calculation is unnecessary.
1858
1859	// The performance of this implementation does not depend on look-up
1860	// tables being on the L1 cache.
1861	return chrono::day{__m != `2` ? (__m ^ (__m >> `3`)) \| `30`
1862	: _M_y.is_leap() ? `29` : `28`};
1863	}
1864
1865	constexpr
1866	operator sys_days() const noexcept
1867	{ return sys_days{year() / month() / day()}; }
1868
1869	explicit constexpr
1870	operator local_days() const noexcept
1871	{ return local_days{sys_days{*this}.time_since_epoch()}; }
1872
1873	constexpr bool
1874	ok() const noexcept
1875	{ return _M_y.ok() && _M_mdl.ok(); }
1876
1877	friend constexpr bool
1878	operator==(const year_month_day_last& __x,
1879	const year_month_day_last& __y) noexcept
1880	{
1881	return __x.year() == __y.year()
1882	&& __x.month_day_last() == __y.month_day_last();
1883	}
1884
1885	friend constexpr strong_ordering
1886	operator<=>(const year_month_day_last& __x,
1887	const year_month_day_last& __y) noexcept
1888	= default;
1889
1890	template<typename = __detail::__months_years_conversion_disambiguator>
1891	friend constexpr year_month_day_last
1892	operator+(const year_month_day_last& __ymdl,
1893	const months& __dm) noexcept
1894	{ return (__ymdl.year() / __ymdl.month() + __dm) / last; }
1895
1896	template<typename = __detail::__months_years_conversion_disambiguator>
1897	friend constexpr year_month_day_last
1898	operator+(const months& __dm,
1899	const year_month_day_last& __ymdl) noexcept
1900	{ return __ymdl + __dm; }
1901
1902	template<typename = __detail::__months_years_conversion_disambiguator>
1903	friend constexpr year_month_day_last
1904	operator-(const year_month_day_last& __ymdl,
1905	const months& __dm) noexcept
1906	{ return __ymdl + -__dm; }
1907
1908	friend constexpr year_month_day_last
1909	operator+(const year_month_day_last& __ymdl,
1910	const years& __dy) noexcept
1911	{ return {__ymdl.year() + __dy, __ymdl.month_day_last()}; }
1912
1913	friend constexpr year_month_day_last
1914	operator+(const years& __dy,
1915	const year_month_day_last& __ymdl) noexcept
1916	{ return __ymdl + __dy; }
1917
1918	friend constexpr year_month_day_last
1919	operator-(const year_month_day_last& __ymdl,
1920	const years& __dy) noexcept
1921	{ return __ymdl + -__dy; }
1922
1923	friend constexpr year_month_day_last
1924	operator/(const year_month& __ym, last_spec) noexcept
1925	{ return {__ym.year(), chrono::month_day_last{__ym.month()}}; }
1926
1927	friend constexpr year_month_day_last
1928	operator/(const chrono::year& __y,
1929	const chrono::month_day_last& __mdl) noexcept
1930	{ return {__y, __mdl}; }
1931
1932	friend constexpr year_month_day_last
1933	operator/(int __y, const chrono::month_day_last& __mdl) noexcept
1934	{ return chrono::year(__y) / __mdl; }
1935
1936	friend constexpr year_month_day_last
1937	operator/(const chrono::month_day_last& __mdl,
1938	const chrono::year& __y) noexcept
1939	{ return __y / __mdl; }
1940
1941	friend constexpr year_month_day_last
1942	operator/(const chrono::month_day_last& __mdl, int __y) noexcept
1943	{ return chrono::year(__y) / __mdl; }
1944	};
1945
1946	// year_month_day ctor from year_month_day_last
1947	constexpr
1948	year_month_day::year_month_day(const year_month_day_last& __ymdl) noexcept
1949	: _M_y{__ymdl.year()}, _M_m{__ymdl.month()}, _M_d{__ymdl.day()}
1950	{ }
1951
1952	constexpr bool
1953	year_month_day::ok() const noexcept
1954	{
1955	if (!_M_y.ok() \|\| !_M_m.ok())
1956	return false;
1957	return chrono::day{`1`} <= _M_d && _M_d <= (_M_y / _M_m / last).day();
1958	}
1959
1960	// YEAR_MONTH_WEEKDAY
1961
1962	class year_month_weekday
1963	{
1964	private:
1965	chrono::year _M_y;
1966	chrono::month _M_m;
1967	chrono::weekday_indexed _M_wdi;
1968
1969	static constexpr year_month_weekday
1970	_S_from_sys_days(const sys_days& __dp)
1971	{
1972	year_month_day __ymd{__dp};
1973	chrono::weekday __wd{__dp};
1974	auto __index = __wd[(unsigned{__ymd.day()} - `1`) / `7` + `1`];
1975	return {__ymd.year(), __ymd.month(), __index};
1976	}
1977
1978	public:
1979	year_month_weekday() = default;
1980
1981	constexpr
1982	year_month_weekday(const chrono::year& __y, const chrono::month& __m,
1983	const chrono::weekday_indexed& __wdi) noexcept
1984	: _M_y{__y}, _M_m{__m}, _M_wdi{__wdi}
1985	{ }
1986
1987	constexpr
1988	year_month_weekday(const sys_days& __dp) noexcept
1989	: year_month_weekday{_S_from_sys_days(__dp)}
1990	{ }
1991
1992	explicit constexpr
1993	year_month_weekday(const local_days& __dp) noexcept
1994	: year_month_weekday{sys_days{__dp.time_since_epoch()}}
1995	{ }
1996
1997	template<typename = __detail::__months_years_conversion_disambiguator>
1998	constexpr year_month_weekday&
1999	operator+=(const months& __m) noexcept
2000	{
2001	*this = *this + __m;
2002	return *this;
2003	}
2004
2005	template<typename = __detail::__months_years_conversion_disambiguator>
2006	constexpr year_month_weekday&
2007	operator-=(const months& __m) noexcept
2008	{
2009	*this = *this - __m;
2010	return *this;
2011	}
2012
2013	constexpr year_month_weekday&
2014	operator+=(const years& __y) noexcept
2015	{
2016	*this = *this + __y;
2017	return *this;
2018	}
2019
2020	constexpr year_month_weekday&
2021	operator-=(const years& __y) noexcept
2022	{
2023	*this = *this - __y;
2024	return *this;
2025	}
2026
2027	constexpr chrono::year
2028	year() const noexcept
2029	{ return _M_y; }
2030
2031	constexpr chrono::month
2032	month() const noexcept
2033	{ return _M_m; }
2034
2035	constexpr chrono::weekday
2036	weekday() const noexcept
2037	{ return _M_wdi.weekday(); }
2038
2039	constexpr unsigned
2040	index() const noexcept
2041	{ return _M_wdi.index(); }
2042
2043	constexpr chrono::weekday_indexed
2044	weekday_indexed() const noexcept
2045	{ return _M_wdi; }
2046
2047	constexpr
2048	operator sys_days() const noexcept
2049	{
2050	auto __d = sys_days{year() / month() / `1`};
2051	return __d + (weekday() - chrono::weekday(__d)
2052	+ days{(static_cast<int>(index())-`1`)*`7`});
2053	}
2054
2055	explicit constexpr
2056	operator local_days() const noexcept
2057	{ return local_days{sys_days{*this}.time_since_epoch()}; }
2058
2059	constexpr bool
2060	ok() const noexcept
2061	{
2062	if (!_M_y.ok() \|\| !_M_m.ok() \|\| !_M_wdi.ok())
2063	return false;
2064	if (_M_wdi.index() <= `4`)
2065	return true;
2066	days __d = (_M_wdi.weekday()
2067	- chrono::weekday{sys_days{_M_y / _M_m / `1`}}
2068	+ days((_M_wdi.index()-`1`)*`7` + `1`));
2069	__glibcxx_assert(__d.count() >= `1`);
2070	return (unsigned)__d.count() <= (unsigned)(_M_y / _M_m / last).day();
2071	}
2072
2073	friend constexpr bool
2074	operator==(const year_month_weekday& __x,
2075	const year_month_weekday& __y) noexcept
2076	{
2077	return __x.year() == __y.year()
2078	&& __x.month() == __y.month()
2079	&& __x.weekday_indexed() == __y.weekday_indexed();
2080	}
2081
2082	template<typename = __detail::__months_years_conversion_disambiguator>
2083	friend constexpr year_month_weekday
2084	operator+(const year_month_weekday& __ymwd, const months& __dm) noexcept
2085	{
2086	return ((__ymwd.year() / __ymwd.month() + __dm)
2087	/ __ymwd.weekday_indexed());
2088	}
2089
2090	template<typename = __detail::__months_years_conversion_disambiguator>
2091	friend constexpr year_month_weekday
2092	operator+(const months& __dm, const year_month_weekday& __ymwd) noexcept
2093	{ return __ymwd + __dm; }
2094
2095	friend constexpr year_month_weekday
2096	operator+(const year_month_weekday& __ymwd, const years& __dy) noexcept
2097	{ return {__ymwd.year() + __dy, __ymwd.month(), __ymwd.weekday_indexed()}; }
2098
2099	friend constexpr year_month_weekday
2100	operator+(const years& __dy, const year_month_weekday& __ymwd) noexcept
2101	{ return __ymwd + __dy; }
2102
2103	template<typename = __detail::__months_years_conversion_disambiguator>
2104	friend constexpr year_month_weekday
2105	operator-(const year_month_weekday& __ymwd, const months& __dm) noexcept
2106	{ return __ymwd + -__dm; }
2107
2108	friend constexpr year_month_weekday
2109	operator-(const year_month_weekday& __ymwd, const years& __dy) noexcept
2110	{ return __ymwd + -__dy; }
2111
2112	friend constexpr year_month_weekday
2113	operator/(const year_month& __ym,
2114	const chrono::weekday_indexed& __wdi) noexcept
2115	{ return {__ym.year(), __ym.month(), __wdi}; }
2116
2117	friend constexpr year_month_weekday
2118	operator/(const chrono::year& __y, const month_weekday& __mwd) noexcept
2119	{ return {__y, __mwd.month(), __mwd.weekday_indexed()}; }
2120
2121	friend constexpr year_month_weekday
2122	operator/(int __y, const month_weekday& __mwd) noexcept
2123	{ return chrono::year(__y) / __mwd; }
2124
2125	friend constexpr year_month_weekday
2126	operator/(const month_weekday& __mwd, const chrono::year& __y) noexcept
2127	{ return __y / __mwd; }
2128
2129	friend constexpr year_month_weekday
2130	operator/(const month_weekday& __mwd, int __y) noexcept
2131	{ return chrono::year(__y) / __mwd; }
2132	};
2133
2134	// YEAR_MONTH_WEEKDAY_LAST
2135
2136	class year_month_weekday_last
2137	{
2138	private:
2139	chrono::year _M_y;
2140	chrono::month _M_m;
2141	chrono::weekday_last _M_wdl;
2142
2143	public:
2144	constexpr
2145	year_month_weekday_last(const chrono::year& __y, const chrono::month& __m,
2146	const chrono::weekday_last& __wdl) noexcept
2147	: _M_y{__y}, _M_m{__m}, _M_wdl{__wdl}
2148	{ }
2149
2150	template<typename = __detail::__months_years_conversion_disambiguator>
2151	constexpr year_month_weekday_last&
2152	operator+=(const months& __m) noexcept
2153	{
2154	*this = *this + __m;
2155	return *this;
2156	}
2157
2158	template<typename = __detail::__months_years_conversion_disambiguator>
2159	constexpr year_month_weekday_last&
2160	operator-=(const months& __m) noexcept
2161	{
2162	*this = *this - __m;
2163	return *this;
2164	}
2165
2166	constexpr year_month_weekday_last&
2167	operator+=(const years& __y) noexcept
2168	{
2169	*this = *this + __y;
2170	return *this;
2171	}
2172
2173	constexpr year_month_weekday_last&
2174	operator-=(const years& __y) noexcept
2175	{
2176	*this = *this - __y;
2177	return *this;
2178	}
2179
2180	constexpr chrono::year
2181	year() const noexcept
2182	{ return _M_y; }
2183
2184	constexpr chrono::month
2185	month() const noexcept
2186	{ return _M_m; }
2187
2188	constexpr chrono::weekday
2189	weekday() const noexcept
2190	{ return _M_wdl.weekday(); }
2191
2192	constexpr chrono::weekday_last
2193	weekday_last() const noexcept
2194	{ return _M_wdl; }
2195
2196	constexpr
2197	operator sys_days() const noexcept
2198	{
2199	const auto __d = sys_days{_M_y / _M_m / last};
2200	return sys_days{(__d - (chrono::weekday{__d}
2201	- _M_wdl.weekday())).time_since_epoch()};
2202	}
2203
2204	explicit constexpr
2205	operator local_days() const noexcept
2206	{ return local_days{sys_days{*this}.time_since_epoch()}; }
2207
2208	constexpr bool
2209	ok() const noexcept
2210	{ return _M_y.ok() && _M_m.ok() && _M_wdl.ok(); }
2211
2212	friend constexpr bool
2213	operator==(const year_month_weekday_last& __x,
2214	const year_month_weekday_last& __y) noexcept
2215	{
2216	return __x.year() == __y.year()
2217	&& __x.month() == __y.month()
2218	&& __x.weekday_last() == __y.weekday_last();
2219	}
2220
2221	template<typename = __detail::__months_years_conversion_disambiguator>
2222	friend constexpr year_month_weekday_last
2223	operator+(const year_month_weekday_last& __ymwdl,
2224	const months& __dm) noexcept
2225	{
2226	return ((__ymwdl.year() / __ymwdl.month() + __dm)
2227	/ __ymwdl.weekday_last());
2228	}
2229
2230	template<typename = __detail::__months_years_conversion_disambiguator>
2231	friend constexpr year_month_weekday_last
2232	operator+(const months& __dm,
2233	const year_month_weekday_last& __ymwdl) noexcept
2234	{ return __ymwdl + __dm; }
2235
2236	friend constexpr year_month_weekday_last
2237	operator+(const year_month_weekday_last& __ymwdl,
2238	const years& __dy) noexcept
2239	{ return {__ymwdl.year() + __dy, __ymwdl.month(), __ymwdl.weekday_last()}; }
2240
2241	friend constexpr year_month_weekday_last
2242	operator+(const years& __dy,
2243	const year_month_weekday_last& __ymwdl) noexcept
2244	{ return __ymwdl + __dy; }
2245
2246	template<typename = __detail::__months_years_conversion_disambiguator>
2247	friend constexpr year_month_weekday_last
2248	operator-(const year_month_weekday_last& __ymwdl,
2249	const months& __dm) noexcept
2250	{ return __ymwdl + -__dm; }
2251
2252	friend constexpr year_month_weekday_last
2253	operator-(const year_month_weekday_last& __ymwdl,
2254	const years& __dy) noexcept
2255	{ return __ymwdl + -__dy; }
2256
2257	friend constexpr year_month_weekday_last
2258	operator/(const year_month& __ym,
2259	const chrono::weekday_last& __wdl) noexcept
2260	{ return {__ym.year(), __ym.month(), __wdl}; }
2261
2262	friend constexpr year_month_weekday_last
2263	operator/(const chrono::year& __y,
2264	const chrono::month_weekday_last& __mwdl) noexcept
2265	{ return {__y, __mwdl.month(), __mwdl.weekday_last()}; }
2266
2267	friend constexpr year_month_weekday_last
2268	operator/(int __y, const chrono::month_weekday_last& __mwdl) noexcept
2269	{ return chrono::year(__y) / __mwdl; }
2270
2271	friend constexpr year_month_weekday_last
2272	operator/(const chrono::month_weekday_last& __mwdl,
2273	const chrono::year& __y) noexcept
2274	{ return __y / __mwdl; }
2275
2276	friend constexpr year_month_weekday_last
2277	operator/(const chrono::month_weekday_last& __mwdl, int __y) noexcept
2278	{ return chrono::year(__y) / __mwdl; }
2279	};
2280
2281	// HH_MM_SS
2282
2283	/// @cond undocumented
2284	namespace __detail
2285	{
2286	consteval long long
2287	__pow10(unsigned __n)
2288	{
2289	long long __r = `1`;
2290	while (__n-- > `0`)
2291	__r *= `10`;
2292	return __r;
2293	}
2294
2295	template<typename _Duration> struct __utc_leap_second;
2296	}
2297	/// @endcond
2298
2299	/* Utility for splitting a duration into hours, minutes, and seconds*
2300	*
2301	* This is a convenience type that provides accessors for the constituent
2302	* parts (hours, minutes, seconds and subseconds) of a duration.
2303	*
2304	* @since C++20
2305	*/
2306	template<typename _Duration>
2307	class hh_mm_ss
2308	{
2309	static_assert( __is_duration<_Duration>::value );
2310
2311	private:
2312	static consteval int
2313	_S_fractional_width()
2314	{
2315	auto __den = _Duration::period::den;
2316	const int __multiplicity_2 = std::__countr_zero((uintmax_t)__den);
2317	__den >>= __multiplicity_2;
2318	int __multiplicity_5 = `0`;
2319	while ((__den % `5`) == `0`)
2320	{
2321	++__multiplicity_5;
2322	__den /= `5`;
2323	}
2324	if (__den != `1`)
2325	return `6`;
2326
2327	int __width = (__multiplicity_2 > __multiplicity_5
2328	? __multiplicity_2 : __multiplicity_5);
2329	if (__width > `18`)
2330	__width = `18`;
2331	return __width;
2332	}
2333
2334	constexpr
2335	hh_mm_ss(_Duration __d, bool __is_neg)
2336	: _M_h (duration_cast<chrono::hours>(__d)),
2337	_M_m (duration_cast<chrono::minutes>(__d - hours())),
2338	_M_s (duration_cast<chrono::seconds>(__d - hours() - minutes())),
2339	_M_is_neg(__is_neg)
2340	{
2341	auto __ss = __d - hours() - minutes() - seconds();
2342	if constexpr (treat_as_floating_point_v<typename precision::rep>)
2343	_M_ss._M_r = __ss.count();
2344	else if constexpr (precision::period::den != `1`)
2345	_M_ss._M_r = duration_cast<precision>(__ss).count();
2346	}
2347
2348	static constexpr _Duration
2349	_S_abs(_Duration __d)
2350	{
2351	if constexpr (numeric_limits<typename _Duration::rep>::is_signed)
2352	return chrono::abs(__d);
2353	else
2354	return __d;
2355	}
2356
2357	public:
2358	static constexpr unsigned fractional_width = {_S_fractional_width()};
2359
2360	using precision
2361	= duration<common_type_t<typename _Duration::rep,
2362	chrono::seconds::rep>,
2363	ratio<`1`, __detail::__pow10(fractional_width)>>;
2364
2365	constexpr hh_mm_ss() noexcept = default;
2366
2367	constexpr explicit
2368	hh_mm_ss(_Duration __d)
2369	: hh_mm_ss(_S_abs(__d), __d < _Duration::zero())
2370	{ }
2371
2372	constexpr bool
2373	is_negative() const noexcept
2374	{
2375	if constexpr (!_S_is_unsigned)
2376	return _M_is_neg;
2377	else
2378	return false;
2379	}
2380
2381	constexpr chrono::hours
2382	hours() const noexcept
2383	{ return _M_h; }
2384
2385	constexpr chrono::minutes
2386	minutes() const noexcept
2387	{ return _M_m; }
2388
2389	constexpr chrono::seconds
2390	seconds() const noexcept
2391	{ return _M_s; }
2392
2393	constexpr precision
2394	subseconds() const noexcept
2395	{ return static_cast<precision>(_M_ss); }
2396
2397	constexpr explicit
2398	operator precision() const noexcept
2399	{ return to_duration(); }
2400
2401	constexpr precision
2402	to_duration() const noexcept
2403	{
2404	if constexpr (!_S_is_unsigned)
2405	if (_M_is_neg)
2406	return -(_M_h + _M_m + _M_s + subseconds());
2407	return _M_h + _M_m + _M_s + subseconds();
2408	}
2409
2410	private:
2411	static constexpr bool _S_is_unsigned
2412	= __and_v<is_integral<typename _Duration::rep>,
2413	is_unsigned<typename _Duration::rep>>;
2414
2415	template<typename _Ratio>
2416	using __byte_duration = duration<unsigned char, _Ratio>;
2417
2418	// The type of the _M_ss member that holds the subsecond precision.
2419	template<typename _Dur>
2420	struct __subseconds
2421	{
2422	typename _Dur::rep _M_r{};
2423
2424	constexpr explicit
2425	operator _Dur() const noexcept
2426	{ return _Dur(_M_r); }
2427	};
2428
2429	// An empty class if this precision doesn't need subseconds.
2430	template<typename _Rep>
2431	requires (!treat_as_floating_point_v<_Rep>)
2432	struct __subseconds<duration<_Rep, ratio<`1`>>>
2433	{
2434	constexpr explicit
2435	operator duration<_Rep, ratio<`1`>>() const noexcept
2436	{ return {}; }
2437	};
2438
2439	template<typename _Rep, typename _Period>
2440	requires (!treat_as_floating_point_v<_Rep>)
2441	&& ratio_less_v<_Period, ratio<`1`, `1`>>
2442	&& ratio_greater_equal_v<_Period, ratio<`1`, `250`>>
2443	struct __subseconds<duration<_Rep, _Period>>
2444	{
2445	unsigned char _M_r{};
2446
2447	constexpr explicit
2448	operator duration<_Rep, _Period>() const noexcept
2449	{ return duration<_Rep, _Period>(_M_r); }
2450	};
2451
2452	template<typename _Rep, typename _Period>
2453	requires (!treat_as_floating_point_v<_Rep>)
2454	&& ratio_less_v<_Period, ratio<`1`, `250`>>
2455	&& ratio_greater_equal_v<_Period, ratio<`1`, `4000000000`>>
2456	struct __subseconds<duration<_Rep, _Period>>
2457	{
2458	uint_least32_t _M_r{};
2459
2460	constexpr explicit
2461	operator duration<_Rep, _Period>() const noexcept
2462	{ return duration<_Rep, _Period>(_M_r); }
2463	};
2464
2465	chrono::hours _M_h{};
2466	__byte_duration<ratio<`60`>> _M_m{};
2467	__byte_duration<ratio<`1`>> _M_s{};
2468	bool _M_is_neg{};
2469	__subseconds<precision> _M_ss{};
2470
2471	template<typename> friend struct __detail::__utc_leap_second;
2472	};
2473
2474	/// @cond undocumented
2475	namespace __detail
2476	{
2477	// Represents a time that is within a leap second insertion.
2478	template<typename _Duration>
2479	struct __utc_leap_second
2480	{
2481	explicit
2482	__utc_leap_second(const sys_time<_Duration>& __s)
2483	: _M_date(chrono::floor<days>(__s)), _M_time(__s - _M_date)
2484	{
2485	++_M_time._M_s;
2486	}
2487
2488	sys_days _M_date;
2489	hh_mm_ss<common_type_t<_Duration, days>> _M_time;
2490	};
2491	}
2492	/// @endcond
2493
2494	// 12/24 HOURS FUNCTIONS
2495
2496	constexpr bool
2497	is_am(const hours& __h) noexcept
2498	{ return `0h` <= __h && __h <= `11h`; }
2499
2500	constexpr bool
2501	is_pm(const hours& __h) noexcept
2502	{ return `12h` <= __h && __h <= `23h`; }
2503
2504	constexpr hours
2505	make12(const hours& __h) noexcept
2506	{
2507	if (__h == `0h`)
2508	return `12h`;
2509	else if (__h > `12h`)
2510	return __h - `12h`;
2511	return __h;
2512	}
2513
2514	constexpr hours
2515	make24(const hours& __h, bool __is_pm) noexcept
2516	{
2517	if (!__is_pm)
2518	{
2519	if (__h == `12h`)
2520	return `0h`;
2521	else
2522	return __h;
2523	}
2524	else
2525	{
2526	if (__h == `12h`)
2527	return __h;
2528	else
2529	return __h + `12h`;
2530	}
2531	}
2532
2533	#if _GLIBCXX_USE_CXX11_ABI \|\| ! _GLIBCXX_USE_DUAL_ABI
2534	// C++20 [time.zones] Time zones
2535
2536	struct tzdb;
2537
2538	struct sys_info
2539	{
2540	sys_seconds begin;
2541	sys_seconds end;
2542	seconds offset;
2543	minutes save;
2544	string abbrev;
2545	};
2546
2547	struct local_info
2548	{
2549	static constexpr int unique = `0`;
2550	static constexpr int nonexistent = `1`;
2551	static constexpr int ambiguous = `2`;
2552
2553	int result;
2554	sys_info first;
2555	sys_info second;
2556	};
2557
2558	class nonexistent_local_time : public runtime_error
2559	{
2560	public:
2561	template<typename _Duration>
2562	nonexistent_local_time(const local_time<_Duration>& __tp,
2563	const local_info& __i)
2564	: runtime_error(_S_make_what_str(__tp, __i))
2565	{ __glibcxx_assert(__i.result == local_info::nonexistent); }
2566
2567	private:
2568	template<typename _Duration>
2569	static string
2570	_S_make_what_str(const local_time<_Duration>& __tp,
2571	const local_info& __i)
2572	{
2573	std::ostringstream __os;
2574	__os << __tp << " is in a gap between\n"
2575	<< local_seconds(__i.first.end.time_since_epoch())
2576	+ __i.first.offset << `' '` << __i.first.abbrev << " and\n"
2577	<< local_seconds(__i.second.begin.time_since_epoch())
2578	+ __i.second.offset << `' '` << __i.second.abbrev
2579	<< " which are both equivalent to\n"
2580	<< __i.first.end << " UTC";
2581	return std::move(__os).str();
2582	}
2583	};
2584
2585	class ambiguous_local_time : public runtime_error
2586	{
2587	public:
2588	template<typename _Duration>
2589	ambiguous_local_time(const local_time<_Duration>& __tp,
2590	const local_info& __i)
2591	: runtime_error(_S_make_what_str(__tp, __i))
2592	{ __glibcxx_assert(__i.result == local_info::ambiguous); }
2593
2594	private:
2595	template<typename _Duration>
2596	static string
2597	_S_make_what_str(const local_time<_Duration>& __tp,
2598	const local_info& __i)
2599	{
2600	std::ostringstream __os;
2601	__os << __tp << " is ambiguous. It could be\n"
2602	<< __tp << `' '` << __i.first.abbrev << " == "
2603	<< __tp - __i.first.offset << " UTC or\n"
2604	<< __tp << `' '` << __i.second.abbrev << " == "
2605	<< __tp - __i.second.offset << " UTC";
2606	return std::move(__os).str();
2607	}
2608	};
2609
2610	template<typename _Duration>
2611	[[noreturn]] void
2612	__throw_bad_local_time(const local_time<_Duration>& __tp,
2613	const local_info& __i)
2614	{
2615	#if __cpp_exceptions
2616	if (__i.result == local_info::nonexistent)
2617	throw nonexistent_local_time(__tp, __i);
2618	throw ambiguous_local_time(__tp, __i);
2619	#else
2620	__builtin_abort();
2621	#endif
2622	}
2623
2624	enum class choose { earliest, latest };
2625
2626	class time_zone
2627	{
2628	public:
2629	time_zone(time_zone&&) = default;
2630	time_zone& operator=(time_zone&&) = default;
2631
2632	~time_zone();
2633
2634	[[nodiscard]]
2635	string_view name() const noexcept { return _M_name; }
2636
2637	template<typename _Duration>
2638	sys_info
2639	get_info(const sys_time<_Duration>& __st) const
2640	{ return _M_get_sys_info(chrono::floor<seconds>(__st)); }
2641
2642	template<typename _Duration>
2643	local_info
2644	get_info(const local_time<_Duration>& __tp) const
2645	{ return _M_get_local_info(chrono::floor<seconds>(__tp)); }
2646
2647	template<typename _Duration>
2648	sys_time<common_type_t<_Duration, seconds>>
2649	to_sys(const local_time<_Duration>& __tp) const
2650	{
2651	local_info __info = get_info(__tp);
2652
2653	if (__info.result != local_info::unique)
2654	__throw_bad_local_time(__tp, __info);
2655
2656	return sys_time<_Duration>(__tp.time_since_epoch())
2657	- __info.first.offset;
2658	}
2659
2660	template<typename _Duration>
2661	sys_time<common_type_t<_Duration, seconds>>
2662	to_sys(const local_time<_Duration>& __tp, choose __z) const
2663	{
2664	local_info __info = get_info(__tp);
2665
2666	if (__info.result == local_info::nonexistent)
2667	return __info.first.end; // Last second of the previous sys_info.
2668
2669	sys_time<_Duration> __st(__tp.time_since_epoch());
2670
2671	if (__info.result == local_info::ambiguous && __z == choose::latest)
2672	return __st - __info.second.offset; // Time in the later sys_info.
2673	// else if __z == earliest, use __info.first.offset as below:
2674
2675	return __st - __info.first.offset;
2676	}
2677
2678	template<typename _Duration>
2679	local_time<common_type_t<_Duration, seconds>>
2680	to_local(const sys_time<_Duration>& __tp) const
2681	{
2682	auto __d = (__tp + get_info(__tp).offset).time_since_epoch();
2683	return local_time<common_type_t<_Duration, seconds>>(__d);
2684	}
2685
2686	[[nodiscard]] friend bool
2687	operator==(const time_zone& __x, const time_zone& __y) noexcept
2688	{ return __x._M_name == __y._M_name; }
2689
2690	[[nodiscard]] friend strong_ordering
2691	operator<=>(const time_zone& __x, const time_zone& __y) noexcept
2692	{ return __x._M_name <=> __y._M_name; }
2693
2694	private:
2695	sys_info _M_get_sys_info(sys_seconds) const;
2696	local_info _M_get_local_info(local_seconds) const;
2697
2698	friend const tzdb& reload_tzdb();
2699	friend struct tzdb;
2700	friend class tzdb_list;
2701
2702	struct _Impl;
2703
2704	explicit time_zone(unique_ptr<_Impl> __p);
2705	string _M_name;
2706	unique_ptr<_Impl> _M_impl;
2707	};
2708
2709	const time_zone* locate_zone(string_view __tz_name);
2710	const time_zone* current_zone();
2711
2712	/* The list of `chrono::tzdb` objects*
2713	*
2714	* A single object of this type is constructed by the C++ runtime,
2715	* and can be accessed by calling `chrono::get_tzdb_list()`.
2716	*
2717	* The front of the list is the current `tzdb` object and can be accessed
2718	* via `chrono::get_tzdb_list().front()` or `chrono::get_tzdb()` or
2719	* `*chrono::get_tzdb_list().begin()`.
2720	*
2721	* The `chrono::reload_tzdb()` function will check for a newer version
2722	* and if found, insert it at the front of the list.
2723	*
2724	* @since C++20
2725	*/
2726	class tzdb_list
2727	{
2728	struct _Node;
2729
2730	public:
2731	tzdb_list(const tzdb_list&) = delete;
2732	tzdb_list& operator=(const tzdb_list&) = delete;
2733
2734	/* An iterator into the `tzdb_list`*
2735	*
2736	* As a extension, in libstdc++ each `tzdb` is reference-counted
2737	* and the `const_iterator` type shares ownership of the object it
2738	* refers to. This ensures that a `tzdb` erased from the list will
2739	* not be destroyed while there is an iterator that refers to it.
2740	*/
2741	class const_iterator
2742	{
2743	public:
2744	using value_type = tzdb;
2745	using reference = const tzdb&;
2746	using pointer = const tzdb*;
2747	using difference_type = ptrdiff_t;
2748	using iterator_category = forward_iterator_tag;
2749
2750	constexpr const_iterator() = default;
2751	const_iterator(const const_iterator&) = default;
2752	const_iterator(const_iterator&&) = default;
2753	const_iterator& operator=(const const_iterator&) = default;
2754	const_iterator& operator=(const_iterator&&) = default;
2755
2756	reference operator() const* noexcept;
2757	pointer operator->() const noexcept { return &**this; }
2758	const_iterator& operator++();
2759	const_iterator operator++(int);
2760
2761	bool operator==(const const_iterator&) const noexcept = default;
2762
2763	private:
2764	explicit const_iterator(const shared_ptr<_Node>&) noexcept;
2765
2766	friend class tzdb_list;
2767
2768	shared_ptr<_Node> _M_node;
2769	void* _M_reserved = nullptr;
2770	};
2771
2772	/* Access the current `tzdb` at the front of the list.*
2773	*
2774	* This returns a reference to the same object as `chrono::get_tzdb()`.
2775	*
2776	* @returns A reference to the current tzdb object.
2777	* @since C++20
2778	*/
2779	const tzdb& front() const noexcept;
2780
2781	/* Remove the tzdb object _after_ the one the iterator refers to.*
2782	*
2783	* Calling this function concurrently with any of `front()`, `begin()`,
2784	* or `end()` does not cause a data race, but in general this function
2785	* is not thread-safe. The behaviour may be undefined if erasing an
2786	* element from the list while another thread is calling the same
2787	* function, or incrementing an iterator into the list, or accessing
2788	* the element being erased (unless it is accessed through an iterator).
2789	*
2790	* @param __p A dereferenceable iterator.
2791	* @returns An iterator the element after the one that was erased
2792	* (or `end()` if there is no such element).
2793	* @since C++20
2794	*/
2795	const_iterator erase_after(const_iterator __p);
2796
2797	const_iterator begin() const noexcept;
2798	const_iterator end() const noexcept { return {}; }
2799	const_iterator cbegin() const noexcept { return begin(); }
2800	const_iterator cend() const noexcept { return end(); }
2801
2802	private:
2803	constexpr explicit tzdb_list(nullptr_t);
2804
2805	friend tzdb_list& get_tzdb_list();
2806	friend const tzdb& get_tzdb();
2807	friend const tzdb& reload_tzdb();
2808	friend struct tzdb;
2809	friend class leap_second;
2810	friend struct time_zone::_Impl;
2811	friend class time_zone_link;
2812	};
2813
2814	class time_zone_link
2815	{
2816	public:
2817	time_zone_link(time_zone_link&&) = default;
2818	time_zone_link& operator=(time_zone_link&&) = default;
2819
2820	string_view name() const noexcept { return _M_name; }
2821	string_view target() const noexcept { return _M_target; }
2822
2823	friend bool
2824	operator==(const time_zone_link& __x, const time_zone_link& __y) noexcept
2825	{ return __x.name() == __y.name(); }
2826
2827	friend strong_ordering
2828	operator<=>(const time_zone_link& __x, const time_zone_link& __y) noexcept
2829	{ return __x.name() <=> __y.name(); }
2830
2831	private:
2832	friend const tzdb& reload_tzdb();
2833	friend struct tzdb_list::_Node;
2834
2835	explicit time_zone_link(nullptr_t) { }
2836
2837	string _M_name;
2838	string _M_target;
2839	};
2840
2841	class leap_second
2842	{
2843	public:
2844	leap_second(const leap_second&) = default;
2845	leap_second& operator=(const leap_second&) = default;
2846
2847	[[nodiscard]]
2848	constexpr sys_seconds
2849	date() const noexcept
2850	{
2851	if (_M_s >= _M_s.zero()) [[likely]]
2852	return sys_seconds(_M_s);
2853	return sys_seconds(-_M_s);
2854	}
2855
2856	[[nodiscard]]
2857	constexpr seconds
2858	value() const noexcept
2859	{
2860	if (_M_s >= _M_s.zero()) [[likely]]
2861	return seconds(`1`);
2862	return seconds(-`1`);
2863	}
2864
2865	// This can be defaulted because the database will never contain two
2866	// leap_second objects with the same date but different signs.
2867	[[nodiscard]] friend constexpr bool
2868	operator==(const leap_second&, const leap_second&) noexcept = default;
2869
2870	[[nodiscard]] friend constexpr strong_ordering
2871	operator<=>(const leap_second& __x, const leap_second& __y) noexcept
2872	{ return __x.date() <=> __y.date(); }
2873
2874	template<typename _Duration>
2875	[[nodiscard]] friend constexpr bool
2876	operator==(const leap_second& __x,
2877	const sys_time<_Duration>& __y) noexcept
2878	{ return __x.date() == __y; }
2879
2880	template<typename _Duration>
2881	[[nodiscard]] friend constexpr bool
2882	operator<(const leap_second& __x,
2883	const sys_time<_Duration>& __y) noexcept
2884	{ return __x.date() < __y; }
2885
2886	template<typename _Duration>
2887	[[nodiscard]] friend constexpr bool
2888	operator<(const sys_time<_Duration>& __x,
2889	const leap_second& __y) noexcept
2890	{ return __x < __y.date(); }
2891
2892	template<typename _Duration>
2893	[[nodiscard]] friend constexpr bool
2894	operator>(const leap_second& __x,
2895	const sys_time<_Duration>& __y) noexcept
2896	{ return __y < __x.date(); }
2897
2898	template<typename _Duration>
2899	[[nodiscard]] friend constexpr bool
2900	operator>(const sys_time<_Duration>& __x,
2901	const leap_second& __y) noexcept
2902	{ return __y.date() < __x; }
2903
2904	template<typename _Duration>
2905	[[nodiscard]] friend constexpr bool
2906	operator<=(const leap_second& __x,
2907	const sys_time<_Duration>& __y) noexcept
2908	{ return !(__y < __x.date()); }
2909
2910	template<typename _Duration>
2911	[[nodiscard]] friend constexpr bool
2912	operator<=(const sys_time<_Duration>& __x,
2913	const leap_second& __y) noexcept
2914	{ return !(__y.date() < __x); }
2915
2916	template<typename _Duration>
2917	[[nodiscard]] friend constexpr bool
2918	operator>=(const leap_second& __x,
2919	const sys_time<_Duration>& __y) noexcept
2920	{ return !(__x.date() < __y); }
2921
2922	template<typename _Duration>
2923	[[nodiscard]] friend constexpr bool
2924	operator>=(const sys_time<_Duration>& __x,
2925	const leap_second& __y) noexcept
2926	{ return !(__x < __y.date()); }
2927
2928	template<three_way_comparable_with<seconds> _Duration>
2929	[[nodiscard]] friend constexpr auto
2930	operator<=>(const leap_second& __x,
2931	const sys_time<_Duration>& __y) noexcept
2932	{ return __x.date() <=> __y; }
2933
2934	private:
2935	explicit leap_second(seconds::rep __s) : _M_s(__s) { }
2936
2937	friend struct tzdb_list::_Node;
2938
2939	friend const tzdb& reload_tzdb();
2940
2941	template<typename _Duration>
2942	friend leap_second_info
2943	get_leap_second_info(const utc_time<_Duration>&);
2944
2945	seconds _M_s; // == date().time_since_epoch() value().count()*
2946	};
2947
2948	template<class _Tp> struct zoned_traits { };
2949
2950	template<>
2951	struct zoned_traits<const time_zone*>
2952	{
2953	static const time_zone*
2954	default_zone()
2955	{ return std::chrono::locate_zone("UTC"); }
2956
2957	static const time_zone*
2958	locate_zone(string_view __name)
2959	{ return std::chrono::locate_zone(__name); }
2960	};
2961
2962	struct tzdb
2963	{
2964	string version;
2965	_GLIBCXX_STD_C::vector<time_zone> zones;
2966	_GLIBCXX_STD_C::vector<time_zone_link> links;
2967	_GLIBCXX_STD_C::vector<leap_second> leap_seconds;
2968
2969	const time_zone*
2970	locate_zone(string_view __tz_name) const;
2971
2972	const time_zone*
2973	current_zone() const;
2974
2975	private:
2976	friend const tzdb& reload_tzdb();
2977	friend class time_zone;
2978	friend struct tzdb_list::_Node;
2979	};
2980
2981	tzdb_list& get_tzdb_list();
2982	const tzdb& get_tzdb();
2983
2984	const tzdb& reload_tzdb();
2985	string remote_version();
2986
2987	template<typename _Duration, typename _TimeZonePtr = const time_zone*>
2988	class zoned_time
2989	{
2990	static_assert(__is_duration_v<_Duration>);
2991
2992	using _Traits = zoned_traits<_TimeZonePtr>;
2993
2994	// Every constructor that accepts a string_view as its first parameter
2995	// does not participate in class template argument deduction.
2996	using string_view = type_identity_t<std::string_view>;
2997
2998	public:
2999	using duration = common_type_t<_Duration, seconds>;
3000
3001	zoned_time() requires requires { _Traits::default_zone(); }
3002	{ }
3003
3004	zoned_time(const zoned_time&) = default;
3005	zoned_time& operator=(const zoned_time&) = default;
3006
3007	zoned_time(const sys_time<_Duration>& __st)
3008	requires requires { _Traits::default_zone(); }
3009	: _M_tp(__st)
3010	{ }
3011
3012	explicit
3013	zoned_time(_TimeZonePtr __z) : _M_zone(std::move(__z)) { }
3014
3015	explicit
3016	zoned_time(string_view __name)
3017	requires requires {
3018	_TimeZonePtr{_Traits::locate_zone(std::string_view{})};
3019	}
3020	: _M_zone(_Traits::locate_zone(__name))
3021	{ }
3022
3023	template<typename _Duration2>
3024	zoned_time(const zoned_time<_Duration2, _TimeZonePtr>& __zt)
3025	requires is_convertible_v<sys_time<_Duration2>, sys_time<_Duration>>
3026	: _M_zone(__zt._M_zone), _M_tp(__zt._M_tp)
3027	{ }
3028
3029	zoned_time(_TimeZonePtr __z, const sys_time<_Duration>& __st)
3030	: _M_zone(std::move(__z)), _M_tp(__st)
3031	{ }
3032
3033	zoned_time(string_view __name, const sys_time<_Duration>& __st)
3034	: zoned_time(_Traits::locate_zone(__name), __st)
3035	{ }
3036
3037	zoned_time(_TimeZonePtr __z, const local_time<_Duration>& __tp)
3038	requires requires {
3039	{ __z->to_sys(__tp) } -> convertible_to<sys_time<_Duration>>;
3040	}
3041	: _M_zone(std::move(__z)), _M_tp(_M_zone->to_sys(__tp))
3042	{ }
3043
3044	zoned_time(string_view __name, const local_time<_Duration>& __tp)
3045	requires requires (_TimeZonePtr __z) {
3046	{ _Traits::locate_zone(__name) } -> convertible_to<_TimeZonePtr>;
3047	{ __z->to_sys(__tp) } -> convertible_to<sys_time<_Duration>>;
3048	}
3049	: zoned_time(_Traits::locate_zone(__name), __tp)
3050	{ }
3051
3052	zoned_time(_TimeZonePtr __z, const local_time<_Duration>& __tp,
3053	choose __c)
3054	requires requires {
3055	{ __z->to_sys(__tp, __c) } -> convertible_to<sys_time<_Duration>>;
3056	}
3057	: _M_zone(std::move(__z)), _M_tp(_M_zone->to_sys(__tp, __c))
3058	{ }
3059
3060	zoned_time(string_view __name, const local_time<_Duration>& __tp,
3061	choose __c)
3062	requires requires (_TimeZonePtr __z) {
3063	{ _Traits::locate_zone(__name) } -> convertible_to<_TimeZonePtr>;
3064	{ __z->to_sys(__tp, __c) } -> convertible_to<sys_time<_Duration>>;
3065	}
3066	: _M_zone(_Traits::locate_zone(__name)),
3067	_M_tp(_M_zone->to_sys(__tp, __c))
3068	{ }
3069
3070	template<typename _Duration2, typename _TimeZonePtr2>
3071	zoned_time(_TimeZonePtr __z,
3072	const zoned_time<_Duration2, _TimeZonePtr2>& __zt)
3073	requires is_convertible_v<sys_time<_Duration2>, sys_time<_Duration>>
3074	: _M_zone(__z), _M_tp(__zt._M_tp)
3075	{ }
3076
3077	template<typename _Duration2, typename _TimeZonePtr2>
3078	zoned_time(_TimeZonePtr __z,
3079	const zoned_time<_Duration2, _TimeZonePtr2>& __zt,
3080	choose)
3081	requires is_convertible_v<sys_time<_Duration2>, sys_time<_Duration>>
3082	: _M_zone(__z), _M_tp(__zt._M_tp)
3083	{ }
3084
3085	template<typename _Duration2, typename _TimeZonePtr2>
3086	zoned_time(string_view __name,
3087	const zoned_time<_Duration2, _TimeZonePtr2>& __zt)
3088	requires is_convertible_v<sys_time<_Duration2>, sys_time<_Duration>>
3089	&& requires {
3090	{ _Traits::locate_zone(__name) } -> convertible_to<_TimeZonePtr>;
3091	}
3092	: _M_zone(_Traits::locate_zone(__name)), _M_tp(__zt._M_tp)
3093	{ }
3094
3095	template<typename _Duration2, typename _TimeZonePtr2>
3096	zoned_time(string_view __name,
3097	const zoned_time<_Duration2, _TimeZonePtr2>& __zt,
3098	choose)
3099	requires is_convertible_v<sys_time<_Duration2>, sys_time<_Duration>>
3100	&& requires {
3101	{ _Traits::locate_zone(__name) } -> convertible_to<_TimeZonePtr>;
3102	}
3103	: _M_zone(_Traits::locate_zone(__name)), _M_tp(__zt._M_tp)
3104	{ }
3105
3106	zoned_time&
3107	operator=(const sys_time<_Duration>& __st)
3108	{
3109	_M_tp = __st;
3110	return *this;
3111	}
3112
3113	zoned_time&
3114	operator=(const local_time<_Duration>& __lt)
3115	{
3116	_M_tp = _M_zone->to_sys(__lt);
3117	return *this;
3118	}
3119
3120	[[nodiscard]]
3121	operator sys_time<duration>() const { return _M_tp; }
3122
3123	[[nodiscard]]
3124	explicit operator local_time<duration>() const
3125	{ return get_local_time(); }
3126
3127	[[nodiscard]]
3128	_TimeZonePtr
3129	get_time_zone() const
3130	{ return _M_zone; }
3131
3132	[[nodiscard]]
3133	local_time<duration>
3134	get_local_time() const
3135	{ return _M_zone->to_local(_M_tp); }
3136
3137	[[nodiscard]]
3138	sys_time<duration>
3139	get_sys_time() const
3140	{ return _M_tp; }
3141
3142	[[nodiscard]]
3143	sys_info
3144	get_info() const
3145	{ return _M_zone->get_info(_M_tp); }
3146
3147	[[nodiscard]] friend bool
3148	operator==(const zoned_time&, const zoned_time&) = default;
3149
3150	private:
3151	_TimeZonePtr _M_zone{ _Traits::default_zone() };
3152	sys_time<duration> _M_tp{};
3153
3154	template<typename _Duration2, typename _TimeZonePtr2>
3155	friend class zoned_time;
3156	};
3157
3158	zoned_time() -> zoned_time<seconds>;
3159
3160	template<typename _Duration>
3161	zoned_time(sys_time<_Duration>)
3162	-> zoned_time<common_type_t<_Duration, seconds>>;
3163
3164	/// @cond undocumented
3165	template<typename _TimeZonePtrOrName>
3166	using __time_zone_representation
3167	= __conditional_t<is_convertible_v<_TimeZonePtrOrName, string_view>,
3168	const time_zone*,
3169	remove_cvref_t<_TimeZonePtrOrName>>;
3170	/// @endcond
3171
3172	template<typename _TimeZonePtrOrName>
3173	zoned_time(_TimeZonePtrOrName&&)
3174	-> zoned_time<seconds, __time_zone_representation<_TimeZonePtrOrName>>;
3175
3176	template<typename _TimeZonePtrOrName, typename _Duration>
3177	zoned_time(_TimeZonePtrOrName&&, sys_time<_Duration>)
3178	-> zoned_time<common_type_t<_Duration, seconds>,
3179	__time_zone_representation<_TimeZonePtrOrName>>;
3180
3181	template<typename _TimeZonePtrOrName, typename _Duration>
3182	zoned_time(_TimeZonePtrOrName&&, local_time<_Duration>,
3183	choose = choose::earliest)
3184	-> zoned_time<common_type_t<_Duration, seconds>,
3185	__time_zone_representation<_TimeZonePtrOrName>>;
3186
3187	template<typename _Duration, typename _TimeZonePtrOrName,
3188	typename _TimeZonePtr2>
3189	zoned_time(_TimeZonePtrOrName&&, zoned_time<_Duration, _TimeZonePtr2>,
3190	choose = choose::earliest)
3191	-> zoned_time<common_type_t<_Duration, seconds>,
3192	__time_zone_representation<_TimeZonePtrOrName>>;
3193
3194	template<typename _Dur1, typename _TZPtr1, typename _Dur2, typename _TZPtr2>
3195	[[nodiscard]]
3196	inline bool
3197	operator==(const zoned_time<_Dur1, _TZPtr1>& __x,
3198	const zoned_time<_Dur2, _TZPtr2>& __y)
3199	{
3200	return __x.get_time_zone() == __y.get_time_zone()
3201	&& __x.get_sys_time() == __y.get_sys_time();
3202	}
3203
3204	using zoned_seconds = zoned_time<seconds>;
3205	#endif // _GLIBCXX_USE_CXX11_ABI \|\| ! _GLIBCXX_USE_DUAL_ABI
3206
3207	namespace __detail
3208	{
3209	inline leap_second_info
3210	__get_leap_second_info(sys_seconds __ss, bool __is_utc)
3211	{
3212	if (__ss < sys_seconds{}) [[unlikely]]
3213	return {};
3214
3215	const seconds::rep __leaps[] {
3216	`78796800`, // 1 Jul 1972
3217	`94694400`, // 1 Jan 1973
3218	`126230400`, // 1 Jan 1974
3219	`157766400`, // 1 Jan 1975
3220	`189302400`, // 1 Jan 1976
3221	`220924800`, // 1 Jan 1977
3222	`252460800`, // 1 Jan 1978
3223	`283996800`, // 1 Jan 1979
3224	`315532800`, // 1 Jan 1980
3225	`362793600`, // 1 Jul 1981
3226	`394329600`, // 1 Jul 1982
3227	`425865600`, // 1 Jul 1983
3228	`489024000`, // 1 Jul 1985
3229	`567993600`, // 1 Jan 1988
3230	`631152000`, // 1 Jan 1990
3231	`662688000`, // 1 Jan 1991
3232	`709948800`, // 1 Jul 1992
3233	`741484800`, // 1 Jul 1993
3234	`773020800`, // 1 Jul 1994
3235	`820454400`, // 1 Jan 1996
3236	`867715200`, // 1 Jul 1997
3237	`915148800`, // 1 Jan 1999
3238	`1136073600`, // 1 Jan 2006
3239	`1230768000`, // 1 Jan 2009
3240	`1341100800`, // 1 Jul 2012
3241	`1435708800`, // 1 Jul 2015
3242	`1483228800`, // 1 Jan 2017
3243	};
3244	// The list above is known to be valid until (at least) this date
3245	// and only contains positive leap seconds.
3246	const sys_seconds __expires(`1735344000s`); // 2024-12-28 00:00:00 UTC
3247
3248	#if _GLIBCXX_USE_CXX11_ABI \|\| ! _GLIBCXX_USE_DUAL_ABI
3249	if (__ss > __expires)
3250	{
3251	// Use updated leap_seconds from tzdb.
3252	size_t __n = std::size(__leaps);
3253
3254	auto __db = get_tzdb_list().begin();
3255	auto __first = __db->leap_seconds.begin() + __n;
3256	auto __last = __db->leap_seconds.end();
3257	auto __pos = std::upper_bound(__first, __last, __ss);
3258	seconds __elapsed(__n);
3259	for (auto __i = __first; __i != __pos; ++__i)
3260	__elapsed += __i->value();
3261
3262	if (__is_utc)
3263	{
3264	// Convert utc_time to sys_time:
3265	__ss -= __elapsed;
3266	// See if that sys_time is before (or during) previous leap sec:
3267	if (__pos != __first && __ss < __pos[-`1`])
3268	{
3269	if ((__ss + `1s`) >= __pos[-`1`])
3270	return {true, __elapsed};
3271	__elapsed -= __pos[-`1`].value();
3272	}
3273	}
3274	return {false, __elapsed};
3275	}
3276	else
3277	#endif
3278	{
3279	seconds::rep __s = __ss.time_since_epoch().count();
3280	const seconds::rep* __first = std::begin(__leaps);
3281	const seconds::rep* __last = std::end(__leaps);
3282
3283	// Don't bother searching the list if we're after the last one.
3284	if (__s > (__last[-`1`] + (__last - __first) + `1`))
3285	return { false, seconds(__last - __first) };
3286
3287	auto __pos = std::upper_bound(__first, __last, __s);
3288	seconds __elapsed{__pos - __first};
3289	if (__is_utc)
3290	{
3291	// Convert utc_time to sys_time:
3292	__s -= __elapsed.count();
3293	// See if that sys_time is before (or during) previous leap sec:
3294	if (__pos != __first && __s < __pos[-`1`])
3295	{
3296	if ((__s + `1`) >= __pos[-`1`])
3297	return {true, __elapsed};
3298	--__elapsed;
3299	}
3300	}
3301	return {false, __elapsed};
3302	}
3303	}
3304	} // namespace __detail
3305
3306	template<typename _Duration>
3307	[[nodiscard]]
3308	inline leap_second_info
3309	get_leap_second_info(const utc_time<_Duration>& __ut)
3310	{
3311	auto __s = chrono::duration_cast<seconds>(__ut.time_since_epoch());
3312	return __detail::__get_leap_second_info(sys_seconds(__s), true);
3313	}
3314
3315	template<typename _Duration>
3316	[[nodiscard]]
3317	inline utc_time<common_type_t<_Duration, seconds>>
3318	utc_clock::from_sys(const sys_time<_Duration>& __t)
3319	{
3320	using _CDur = common_type_t<_Duration, seconds>;
3321	auto __s = chrono::time_point_cast<seconds>(__t);
3322	const auto __li = __detail::__get_leap_second_info(__s, false);
3323	return utc_time<_CDur>{__t.time_since_epoch()} + __li.elapsed;
3324	}
3325
3326	/// @} group chrono
3327	#endif // C++20
3328	} // namespace chrono
3329
3330	#if __cplusplus >= 202002L
3331	inline namespace literals
3332	{
3333	inline namespace chrono_literals
3334	{
3335	/// @addtogroup chrono
3336	/// @{
3337	#pragma GCC diagnostic push
3338	#pragma GCC diagnostic ignored "-Wliteral-suffix"
3339	/// Literal suffix for creating chrono::day objects.
3340	/// @since C++20
3341	constexpr chrono::day
3342	operator""d(unsigned long long __d) noexcept
3343	{ return chrono::day{static_cast<unsigned>(__d)}; }
3344
3345	/// Literal suffix for creating chrono::year objects.
3346	/// @since C++20
3347	constexpr chrono::year
3348	operator""y(unsigned long long __y) noexcept
3349	{ return chrono::year{static_cast<int>(__y)}; }
3350	#pragma GCC diagnostic pop
3351	/// @}
3352	} // inline namespace chrono_literals
3353	} // inline namespace literals
3354	#endif // C++20
3355
3356	_GLIBCXX_END_NAMESPACE_VERSION
3357	} // namespace std
3358
3359	#if __cplusplus >= 202002L
3360	# include <bits/chrono_io.h>
3361	#endif
3362
3363	#endif // C++11
3364
3365	#endif //_GLIBCXX_CHRONO
3366

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