1	// <chrono> -*- C++ -*-
2
3	// Copyright (C) 2008-2023 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	#if __cplusplus >= 202002L
54	// TODO formatting and parsing
55	// # undef __cpp_lib_chrono
56	// # define __cpp_lib_chrono 201907L
57	#endif
58
59	namespace std _GLIBCXX_VISIBILITY(default)
60	{
61	_GLIBCXX_BEGIN_NAMESPACE_VERSION
62
63	/**
64	* @defgroup chrono Time
65	* @ingroup utilities
66	*
67	* Classes and functions for time.
68	*
69	* @since C++11
70	*/
71
72	/** @namespace std::chrono
73	* @brief ISO C++ 2011 namespace for date and time utilities
74	* @ingroup chrono
75	*/
76	namespace chrono
77	{
78	#if __cplusplus >= 202002L
79	/// @addtogroup chrono
80	/// @{
81	struct local_t { };
82	template<typename _Duration>
83	using local_time = time_point<local_t, _Duration>;
84	using local_seconds = local_time<seconds>;
85	using local_days = local_time<days>;
86
87	class utc_clock;
88	class tai_clock;
89	class gps_clock;
90
91	template<typename _Duration>
92	using utc_time = time_point<utc_clock, _Duration>;
93	using utc_seconds = utc_time<seconds>;
94
95	template<typename _Duration>
96	using tai_time = time_point<tai_clock, _Duration>;
97	using tai_seconds = tai_time<seconds>;
98
99	template<typename _Duration>
100	using gps_time = time_point<gps_clock, _Duration>;
101	using gps_seconds = gps_time<seconds>;
102
103	template<> struct is_clock<utc_clock> : true_type { };
104	template<> struct is_clock<tai_clock> : true_type { };
105	template<> struct is_clock<gps_clock> : true_type { };
106
107	template<> inline constexpr bool is_clock_v<utc_clock> = true;
108	template<> inline constexpr bool is_clock_v<tai_clock> = true;
109	template<> inline constexpr bool is_clock_v<gps_clock> = true;
110
111	struct leap_second_info
112	{
113	bool is_leap_second;
114	seconds elapsed;
115	};
116
117	template<typename _Duration>
118	leap_second_info
119	get_leap_second_info(const utc_time<_Duration>& __ut);
120
121	/** A clock that measures Universal Coordinated Time (UTC).
122	*
123	* The epoch is 1970-01-01 00:00:00.
124	*
125	* @since C++20
126	*/
127	class utc_clock
128	{
129	public:
130	using rep = system_clock::rep;
131	using period = system_clock::period;
132	using duration = chrono::duration<rep, period>;
133	using time_point = chrono::time_point<utc_clock>;
134	static constexpr bool is_steady = false;
135
136	[[nodiscard]]
137	static time_point
138	now()
139	{ return from_sys(system_clock::now()); }
140
141	template<typename _Duration>
142	[[nodiscard]]
143	static sys_time<common_type_t<_Duration, seconds>>
144	to_sys(const utc_time<_Duration>& __t)
145	{
146	using _CDur = common_type_t<_Duration, seconds>;
147	const auto __li = chrono::get_leap_second_info(__t);
148	sys_time<_CDur> __s{__t.time_since_epoch() - __li.elapsed};
149	if (__li.is_leap_second)
150	__s = chrono::floor<seconds>(__s) + seconds{1} - _CDur{1};
151	return __s;
152	}
153
154	template<typename _Duration>
155	[[nodiscard]]
156	static utc_time<common_type_t<_Duration, seconds>>
157	from_sys(const sys_time<_Duration>& __t);
158	};
159
160	/** A clock that measures International Atomic Time.
161	*
162	* The epoch is 1958-01-01 00:00:00.
163	*
164	* @since C++20
165	*/
166	class tai_clock
167	{
168	public:
169	using rep = system_clock::rep;
170	using period = system_clock::period;
171	using duration = chrono::duration<rep, period>;
172	using time_point = chrono::time_point<tai_clock>;
173	static constexpr bool is_steady = false; // XXX true for CLOCK_TAI?
174
175	// TODO move into lib, use CLOCK_TAI on linux, add extension point.
176	[[nodiscard]]
177	static time_point
178	now()
179	{ return from_utc(utc_clock::now()); }
180
181	template<typename _Duration>
182	[[nodiscard]]
183	static utc_time<common_type_t<_Duration, seconds>>
184	to_utc(const tai_time<_Duration>& __t)
185	{
186	using _CDur = common_type_t<_Duration, seconds>;
187	return utc_time<_CDur>{__t.time_since_epoch()} - 378691210s;
188	}
189
190	template<typename _Duration>
191	[[nodiscard]]
192	static tai_time<common_type_t<_Duration, seconds>>
193	from_utc(const utc_time<_Duration>& __t)
194	{
195	using _CDur = common_type_t<_Duration, seconds>;
196	return tai_time<_CDur>{__t.time_since_epoch()} + 378691210s;
197	}
198	};
199
200	/** A clock that measures GPS time.
201	*
202	* The epoch is 1980-01-06 00:00:00.
203	*
204	* @since C++20
205	*/
206	class gps_clock
207	{
208	public:
209	using rep = system_clock::rep;
210	using period = system_clock::period;
211	using duration = chrono::duration<rep, period>;
212	using time_point = chrono::time_point<gps_clock>;
213	static constexpr bool is_steady = false; // XXX
214
215	// TODO move into lib, add extension point.
216	[[nodiscard]]
217	static time_point
218	now()
219	{ return from_utc(utc_clock::now()); }
220
221	template<typename _Duration>
222	[[nodiscard]]
223	static utc_time<common_type_t<_Duration, seconds>>
224	to_utc(const gps_time<_Duration>& __t)
225	{
226	using _CDur = common_type_t<_Duration, seconds>;
227	return utc_time<_CDur>{__t.time_since_epoch()} + 315964809s;
228	}
229
230	template<typename _Duration>
231	[[nodiscard]]
232	static gps_time<common_type_t<_Duration, seconds>>
233	from_utc(const utc_time<_Duration>& __t)
234	{
235	using _CDur = common_type_t<_Duration, seconds>;
236	return gps_time<_CDur>{__t.time_since_epoch()} - 315964809s;
237	}
238	};
239
240
241	template<typename _DestClock, typename _SourceClock>
242	struct clock_time_conversion
243	{ };
244
245	// Identity conversions
246
247	template<typename _Clock>
248	struct clock_time_conversion<_Clock, _Clock>
249	{
250	template<typename _Duration>
251	time_point<_Clock, _Duration>
252	operator()(const time_point<_Clock, _Duration>& __t) const
253	{ return __t; }
254	};
255
256	template<>
257	struct clock_time_conversion<system_clock, system_clock>
258	{
259	template<typename _Duration>
260	sys_time<_Duration>
261	operator()(const sys_time<_Duration>& __t) const
262	{ return __t; }
263	};
264
265	template<>
266	struct clock_time_conversion<utc_clock, utc_clock>
267	{
268	template<typename _Duration>
269	utc_time<_Duration>
270	operator()(const utc_time<_Duration>& __t) const
271	{ return __t; }
272	};
273
274	// Conversions between system_clock and utc_clock
275
276	template<>
277	struct clock_time_conversion<utc_clock, system_clock>
278	{
279	template<typename _Duration>
280	utc_time<common_type_t<_Duration, seconds>>
281	operator()(const sys_time<_Duration>& __t) const
282	{ return utc_clock::from_sys(__t); }
283	};
284
285	template<>
286	struct clock_time_conversion<system_clock, utc_clock>
287	{
288	template<typename _Duration>
289	sys_time<common_type_t<_Duration, seconds>>
290	operator()(const utc_time<_Duration>& __t) const
291	{ return utc_clock::to_sys(__t); }
292	};
293
294	template<typename _Tp, typename _Clock>
295	inline constexpr bool __is_time_point_for_v = false;
296
297	template<typename _Clock, typename _Duration>
298	inline constexpr bool
299	__is_time_point_for_v<time_point<_Clock, _Duration>, _Clock> = true;
300
301	// Conversions between system_clock and other clocks
302
303	template<typename _SourceClock>
304	struct clock_time_conversion<system_clock, _SourceClock>
305	{
306	template<typename _Duration, typename _Src = _SourceClock>
307	auto
308	operator()(const time_point<_SourceClock, _Duration>& __t) const
309	-> decltype(_Src::to_sys(__t))
310	{
311	using _Ret = decltype(_SourceClock::to_sys(__t));
312	static_assert(__is_time_point_for_v<_Ret, system_clock>);
313	return _SourceClock::to_sys(__t);
314	}
315	};
316
317	template<typename _DestClock>
318	struct clock_time_conversion<_DestClock, system_clock>
319	{
320	template<typename _Duration, typename _Dest = _DestClock>
321	auto
322	operator()(const sys_time<_Duration>& __t) const
323	-> decltype(_Dest::from_sys(__t))
324	{
325	using _Ret = decltype(_DestClock::from_sys(__t));
326	static_assert(__is_time_point_for_v<_Ret, _DestClock>);
327	return _DestClock::from_sys(__t);
328	}
329	};
330
331	// Conversions between utc_clock and other clocks
332
333	template<typename _SourceClock>
334	struct clock_time_conversion<utc_clock, _SourceClock>
335	{
336	template<typename _Duration, typename _Src = _SourceClock>
337	auto
338	operator()(const time_point<_SourceClock, _Duration>& __t) const
339	-> decltype(_Src::to_utc(__t))
340	{
341	using _Ret = decltype(_SourceClock::to_utc(__t));
342	static_assert(__is_time_point_for_v<_Ret, utc_clock>);
343	return _SourceClock::to_utc(__t);
344	}
345	};
346
347	template<typename _DestClock>
348	struct clock_time_conversion<_DestClock, utc_clock>
349	{
350	template<typename _Duration, typename _Dest = _DestClock>
351	auto
352	operator()(const utc_time<_Duration>& __t) const
353	-> decltype(_Dest::from_utc(__t))
354	{
355	using _Ret = decltype(_DestClock::from_utc(__t));
356	static_assert(__is_time_point_for_v<_Ret, _DestClock>);
357	return _DestClock::from_utc(__t);
358	}
359	};
360
361	/// @cond undocumented
362	namespace __detail
363	{
364	template<typename _DestClock, typename _SourceClock, typename _Duration>
365	concept __clock_convs
366	= requires (const time_point<_SourceClock, _Duration>& __t) {
367	clock_time_conversion<_DestClock, _SourceClock>{}(__t);
368	};
369
370	template<typename _DestClock, typename _SourceClock, typename _Duration>
371	concept __clock_convs_sys
372	= requires (const time_point<_SourceClock, _Duration>& __t) {
373	clock_time_conversion<_DestClock, system_clock>{}(
374	clock_time_conversion<system_clock, _SourceClock>{}(__t));
375	};
376
377	template<typename _DestClock, typename _SourceClock, typename _Duration>
378	concept __clock_convs_utc
379	= requires (const time_point<_SourceClock, _Duration>& __t) {
380	clock_time_conversion<_DestClock, utc_clock>{}(
381	clock_time_conversion<utc_clock, _SourceClock>{}(__t));
382	};
383
384	template<typename _DestClock, typename _SourceClock, typename _Duration>
385	concept __clock_convs_sys_utc
386	= requires (const time_point<_SourceClock, _Duration>& __t) {
387	clock_time_conversion<_DestClock, utc_clock>{}(
388	clock_time_conversion<utc_clock, system_clock>{}(
389	clock_time_conversion<system_clock, _SourceClock>{}(__t)));
390	};
391
392	template<typename _DestClock, typename _SourceClock, typename _Duration>
393	concept __clock_convs_utc_sys
394	= requires (const time_point<_SourceClock, _Duration>& __t) {
395	clock_time_conversion<_DestClock, system_clock>{}(
396	clock_time_conversion<system_clock, utc_clock>{}(
397	clock_time_conversion<utc_clock, _SourceClock>{}(__t)));
398	};
399
400	} // namespace __detail
401	/// @endcond
402
403	/// Convert a time point to a different clock.
404	template<typename _DestClock, typename _SourceClock, typename _Duration>
405	[[nodiscard]]
406	inline auto
407	clock_cast(const time_point<_SourceClock, _Duration>& __t)
408	requires __detail::__clock_convs<_DestClock, _SourceClock, _Duration>
409	|| __detail::__clock_convs_sys<_DestClock, _SourceClock, _Duration>
410	|| __detail::__clock_convs_utc<_DestClock, _SourceClock, _Duration>
411	|| __detail::__clock_convs_sys_utc<_DestClock, _SourceClock, _Duration>
412	|| __detail::__clock_convs_utc_sys<_DestClock, _SourceClock, _Duration>
413	{
414	constexpr bool __direct
415	= __detail::__clock_convs<_DestClock, _SourceClock, _Duration>;
416	if constexpr (__direct)
417	{
418	return clock_time_conversion<_DestClock, _SourceClock>{}(__t);
419	}
420	else
421	{
422	constexpr bool __convert_via_sys_clock
423	= __detail::__clock_convs_sys<_DestClock, _SourceClock, _Duration>;
424	constexpr bool __convert_via_utc_clock
425	= __detail::__clock_convs_utc<_DestClock, _SourceClock, _Duration>;
426	if constexpr (__convert_via_sys_clock)
427	{
428	static_assert(!__convert_via_utc_clock,
429	"clock_cast requires a unique best conversion, but "
430	"conversion is possible via system_clock and also via"
431	"utc_clock");
432	return clock_time_conversion<_DestClock, system_clock>{}(
433	clock_time_conversion<system_clock, _SourceClock>{}(__t));
434	}
435	else if constexpr (__convert_via_utc_clock)
436	{
437	return clock_time_conversion<_DestClock, utc_clock>{}(
438	clock_time_conversion<utc_clock, _SourceClock>{}(__t));
439	}
440	else
441	{
442	constexpr bool __convert_via_sys_and_utc_clocks
443	= __detail::__clock_convs_sys_utc<_DestClock,
444	_SourceClock,
445	_Duration>;
446
447	if constexpr (__convert_via_sys_and_utc_clocks)
448	{
449	constexpr bool __convert_via_utc_and_sys_clocks
450	= __detail::__clock_convs_utc_sys<_DestClock,
451	_SourceClock,
452	_Duration>;
453	static_assert(!__convert_via_utc_and_sys_clocks,
454	"clock_cast requires a unique best conversion, but "
455	"conversion is possible via system_clock followed by "
456	"utc_clock, and also via utc_clock followed by "
457	"system_clock");
458	return clock_time_conversion<_DestClock, utc_clock>{}(
459	clock_time_conversion<utc_clock, system_clock>{}(
460	clock_time_conversion<system_clock, _SourceClock>{}(__t)));
461	}
462	else
463	{
464	return clock_time_conversion<_DestClock, system_clock>{}(
465	clock_time_conversion<system_clock, utc_clock>{}(
466	clock_time_conversion<utc_clock, _SourceClock>{}(__t)));
467	}
468	}
469	}
470	}
471
472	// CALENDRICAL TYPES
473
474	// CLASS DECLARATIONS
475	class day;
476	class month;
477	class year;
478	class weekday;
479	class weekday_indexed;
480	class weekday_last;
481	class month_day;
482	class month_day_last;
483	class month_weekday;
484	class month_weekday_last;
485	class year_month;
486	class year_month_day;
487	class year_month_day_last;
488	class year_month_weekday;
489	class year_month_weekday_last;
490
491	struct last_spec
492	{
493	explicit last_spec() = default;
494
495	friend constexpr month_day_last
496	operator/(int __m, last_spec) noexcept;
497
498	friend constexpr month_day_last
499	operator/(last_spec, int __m) noexcept;
500	};
501
502	inline constexpr last_spec last{};
503
504	namespace __detail
505	{
506	// Helper to __add_modulo and __sub_modulo.
507	template <unsigned __d, typename _Tp>
508	consteval auto
509	__modulo_offset()
510	{
511	using _Up = make_unsigned_t<_Tp>;
512	auto constexpr __a = _Up(-1) - _Up(255 + __d - 2);
513	auto constexpr __b = _Up(__d * (__a / __d) - 1);
514	// Notice: b <= a - 1 <= _Up(-1) - (255 + d - 1) and b % d = d - 1.
515	return _Up(-1) - __b; // >= 255 + d - 1
516	}
517
518	// Compute the remainder of the Euclidean division of __x + __y divided by
519	// __d without overflowing. Typically, __x <= 255 + d - 1 is sum of
520	// weekday/month with a shift in [0, d - 1] and __y is a duration count.
521	template <unsigned __d, typename _Tp>
522	constexpr unsigned
523	__add_modulo(unsigned __x, _Tp __y)
524	{
525	using _Up = make_unsigned_t<_Tp>;
526	// For __y >= 0, _Up(__y) has the same mathematical value as __y and
527	// this function simply returns (__x + _Up(__y)) % d. Typically, this
528	// doesn't overflow since the range of _Up contains many more positive
529	// values than _Tp's. For __y < 0, _Up(__y) has a mathematical value in
530	// the upper-half range of _Up so that adding a positive value to it
531	// might overflow. Moreover, most likely, _Up(__y) != __y mod d. To
532	// fix both issues we subtract from _Up(__y) an __offset >=
533	// 255 + d - 1 to make room for the addition to __x and shift the modulo
534	// to the correct value.
535	auto const __offset = __y >= 0 ? _Up(0) : __modulo_offset<__d, _Tp>();
536	return (__x + _Up(__y) - __offset) % __d;
537	}
538
539	// Similar to __add_modulo but for __x - __y.
540	template <unsigned __d, typename _Tp>
541	constexpr unsigned
542	__sub_modulo(unsigned __x, _Tp __y)
543	{
544	using _Up = make_unsigned_t<_Tp>;
545	auto const __offset = __y <= 0 ? _Up(0) : __modulo_offset<__d, _Tp>();
546	return (__x - _Up(__y) - __offset) % __d;
547	}
548
549	inline constexpr unsigned __days_per_month[12]
550	= { 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
551	}
552
553	// DAY
554
555	class day
556	{
557	private:
558	unsigned char _M_d;
559
560	public:
561	day() = default;
562
563	explicit constexpr
564	day(unsigned __d) noexcept
565	: _M_d(__d)
566	{ }
567
568	constexpr day&
569	operator++() noexcept
570	{
571	++_M_d;
572	return *this;
573	}
574
575	constexpr day
576	operator++(int) noexcept
577	{
578	auto __ret = *this;
579	++(*this);
580	return __ret;
581	}
582
583	constexpr day&
584	operator--() noexcept
585	{
586	--_M_d;
587	return *this;
588	}
589
590	constexpr day
591	operator--(int) noexcept
592	{
593	auto __ret = *this;
594	--(*this);
595	return __ret;
596	}
597
598	constexpr day&
599	operator+=(const days& __d) noexcept
600	{
601	*this = *this + __d;
602	return *this;
603	}
604
605	constexpr day&
606	operator-=(const days& __d) noexcept
607	{
608	*this = *this - __d;
609	return *this;
610	}
611
612	constexpr explicit
613	operator unsigned() const noexcept
614	{ return _M_d; }
615
616	constexpr bool
617	ok() const noexcept
618	{ return 1 <= _M_d && _M_d <= 31; }
619
620	friend constexpr bool
621	operator==(const day& __x, const day& __y) noexcept
622	{ return unsigned{__x} == unsigned{__y}; }
623
624	friend constexpr strong_ordering
625	operator<=>(const day& __x, const day& __y) noexcept
626	{ return unsigned{__x} <=> unsigned{__y}; }
627
628	friend constexpr day
629	operator+(const day& __x, const days& __y) noexcept
630	{ return day(unsigned{__x} + __y.count()); }
631
632	friend constexpr day
633	operator+(const days& __x, const day& __y) noexcept
634	{ return __y + __x; }
635
636	friend constexpr day
637	operator-(const day& __x, const days& __y) noexcept
638	{ return __x + -__y; }
639
640	friend constexpr days
641	operator-(const day& __x, const day& __y) noexcept
642	{ return days{int(unsigned{__x}) - int(unsigned{__y})}; }
643
644	friend constexpr month_day
645	operator/(const month& __m, const day& __d) noexcept;
646
647	friend constexpr month_day
648	operator/(int __m, const day& __d) noexcept;
649
650	friend constexpr month_day
651	operator/(const day& __d, const month& __m) noexcept;
652
653	friend constexpr month_day
654	operator/(const day& __d, int __m) noexcept;
655
656	friend constexpr year_month_day
657	operator/(const year_month& __ym, const day& __d) noexcept;
658	};
659
660	// MONTH
661
662	class month
663	{
664	private:
665	unsigned char _M_m;
666
667	public:
668	month() = default;
669
670	explicit constexpr
671	month(unsigned __m) noexcept
672	: _M_m(__m)
673	{ }
674
675	constexpr month&
676	operator++() noexcept
677	{
678	*this += months{1};
679	return *this;
680	}
681
682	constexpr month
683	operator++(int) noexcept
684	{
685	auto __ret = *this;
686	++(*this);
687	return __ret;
688	}
689
690	constexpr month&
691	operator--() noexcept
692	{
693	*this -= months{1};
694	return *this;
695	}
696
697	constexpr month
698	operator--(int) noexcept
699	{
700	auto __ret = *this;
701	--(*this);
702	return __ret;
703	}
704
705	constexpr month&
706	operator+=(const months& __m) noexcept
707	{
708	*this = *this + __m;
709	return *this;
710	}
711
712	constexpr month&
713	operator-=(const months& __m) noexcept
714	{
715	*this = *this - __m;
716	return *this;
717	}
718
719	explicit constexpr
720	operator unsigned() const noexcept
721	{ return _M_m; }
722
723	constexpr bool
724	ok() const noexcept
725	{ return 1 <= _M_m && _M_m <= 12; }
726
727	friend constexpr bool
728	operator==(const month& __x, const month& __y) noexcept
729	{ return unsigned{__x} == unsigned{__y}; }
730
731	friend constexpr strong_ordering
732	operator<=>(const month& __x, const month& __y) noexcept
733	{ return unsigned{__x} <=> unsigned{__y}; }
734
735	friend constexpr month
736	operator+(const month& __x, const months& __y) noexcept
737	{
738	// modulo(x + (y - 1), 12) = modulo(x + (y - 1) + 12, 12)
739	// = modulo((x + 11) + y , 12)
740	return month{1 + __detail::__add_modulo<12>(
741	unsigned{__x} + 11, __y.count())};
742	}
743
744	friend constexpr month
745	operator+(const months& __x, const month& __y) noexcept
746	{ return __y + __x; }
747
748	friend constexpr month
749	operator-(const month& __x, const months& __y) noexcept
750	{
751	// modulo(x + (-y - 1), 12) = modulo(x + (-y - 1) + 12, 12)
752	// = modulo((x + 11) - y , 12)
753	return month{1 + __detail::__sub_modulo<12>(
754	unsigned{__x} + 11, __y.count())};
755	}
756
757	friend constexpr months
758	operator-(const month& __x, const month& __y) noexcept
759	{
760	const auto __dm = int(unsigned(__x)) - int(unsigned(__y));
761	return months{__dm < 0 ? 12 + __dm : __dm};
762	}
763
764	friend constexpr year_month
765	operator/(const year& __y, const month& __m) noexcept;
766
767	friend constexpr month_day
768	operator/(const month& __m, int __d) noexcept;
769
770	friend constexpr month_day_last
771	operator/(const month& __m, last_spec) noexcept;
772
773	friend constexpr month_day_last
774	operator/(last_spec, const month& __m) noexcept;
775
776	friend constexpr month_weekday
777	operator/(const month& __m, const weekday_indexed& __wdi) noexcept;
778
779	friend constexpr month_weekday
780	operator/(const weekday_indexed& __wdi, const month& __m) noexcept;
781
782	friend constexpr month_weekday_last
783	operator/(const month& __m, const weekday_last& __wdl) noexcept;
784
785	friend constexpr month_weekday_last
786	operator/(const weekday_last& __wdl, const month& __m) noexcept;
787	};
788
789	inline constexpr month January{1};
790	inline constexpr month February{2};
791	inline constexpr month March{3};
792	inline constexpr month April{4};
793	inline constexpr month May{5};
794	inline constexpr month June{6};
795	inline constexpr month July{7};
796	inline constexpr month August{8};
797	inline constexpr month September{9};
798	inline constexpr month October{10};
799	inline constexpr month November{11};
800	inline constexpr month December{12};
801
802	// YEAR
803
804	class year
805	{
806	private:
807	short _M_y;
808
809	public:
810	year() = default;
811
812	explicit constexpr
813	year(int __y) noexcept
814	: _M_y{static_cast<short>(__y)}
815	{ }
816
817	static constexpr year
818	min() noexcept
819	{ return year{-32767}; }
820
821	static constexpr year
822	max() noexcept
823	{ return year{32767}; }
824
825	constexpr year&
826	operator++() noexcept
827	{
828	++_M_y;
829	return *this;
830	}
831
832	constexpr year
833	operator++(int) noexcept
834	{
835	auto __ret = *this;
836	++(*this);
837	return __ret;
838	}
839
840	constexpr year&
841	operator--() noexcept
842	{
843	--_M_y;
844	return *this;
845	}
846
847	constexpr year
848	operator--(int) noexcept
849	{
850	auto __ret = *this;
851	--(*this);
852	return __ret;
853	}
854
855	constexpr year&
856	operator+=(const years& __y) noexcept
857	{
858	*this = *this + __y;
859	return *this;
860	}
861
862	constexpr year&
863	operator-=(const years& __y) noexcept
864	{
865	*this = *this - __y;
866	return *this;
867	}
868
869	constexpr year
870	operator+() const noexcept
871	{ return *this; }
872
873	constexpr year
874	operator-() const noexcept
875	{ return year{-_M_y}; }
876
877	constexpr bool
878	is_leap() const noexcept
879	{
880	// Testing divisibility by 100 first gives better performance [1], i.e.,
881	// return _M_y % 100 == 0 ? _M_y % 400 == 0 : _M_y % 16 == 0;
882	// Furthermore, if _M_y % 100 == 0, then _M_y % 400 == 0 is equivalent
883	// to _M_y % 16 == 0, so we can simplify it to
884	// return _M_y % 100 == 0 ? _M_y % 16 == 0 : _M_y % 4 == 0. // #1
885	// Similarly, we can replace 100 with 25 (which is good since
886	// _M_y % 25 == 0 requires one fewer instruction than _M_y % 100 == 0
887	// [2]):
888	// return _M_y % 25 == 0 ? _M_y % 16 == 0 : _M_y % 4 == 0. // #2
889	// Indeed, first assume _M_y % 4 != 0. Then _M_y % 16 != 0 and hence,
890	// _M_y % 4 == 0 and _M_y % 16 == 0 are both false. Therefore, #2
891	// returns false as it should (regardless of _M_y % 25.) Now assume
892	// _M_y % 4 == 0. In this case, _M_y % 25 == 0 if, and only if,
893	// _M_y % 100 == 0, that is, #1 and #2 are equivalent. Finally, #2 is
894	// equivalent to
895	// return (_M_y & (_M_y % 25 == 0 ? 15 : 3)) == 0.
896
897	// References:
898	// [1] https://github.com/cassioneri/calendar
899	// [2] https://godbolt.org/z/55G8rn77e
900	// [3] https://gcc.gnu.org/pipermail/libstdc++/2021-June/052815.html
901
902	return (_M_y & (_M_y % 25 == 0 ? 15 : 3)) == 0;
903	}
904
905	explicit constexpr
906	operator int() const noexcept
907	{ return _M_y; }
908
909	constexpr bool
910	ok() const noexcept
911	{ return min()._M_y <= _M_y && _M_y <= max()._M_y; }
912
913	friend constexpr bool
914	operator==(const year& __x, const year& __y) noexcept
915	{ return int{__x} == int{__y}; }
916
917	friend constexpr strong_ordering
918	operator<=>(const year& __x, const year& __y) noexcept
919	{ return int{__x} <=> int{__y}; }
920
921	friend constexpr year
922	operator+(const year& __x, const years& __y) noexcept
923	{ return year{int{__x} + static_cast<int>(__y.count())}; }
924
925	friend constexpr year
926	operator+(const years& __x, const year& __y) noexcept
927	{ return __y + __x; }
928
929	friend constexpr year
930	operator-(const year& __x, const years& __y) noexcept
931	{ return __x + -__y; }
932
933	friend constexpr years
934	operator-(const year& __x, const year& __y) noexcept
935	{ return years{int{__x} - int{__y}}; }
936
937	friend constexpr year_month
938	operator/(const year& __y, int __m) noexcept;
939
940	friend constexpr year_month_day
941	operator/(const year& __y, const month_day& __md) noexcept;
942
943	friend constexpr year_month_day
944	operator/(const month_day& __md, const year& __y) noexcept;
945
946	friend constexpr year_month_day_last
947	operator/(const year& __y, const month_day_last& __mdl) noexcept;
948
949	friend constexpr year_month_day_last
950	operator/(const month_day_last& __mdl, const year& __y) noexcept;
951
952	friend constexpr year_month_weekday
953	operator/(const year& __y, const month_weekday& __mwd) noexcept;
954
955	friend constexpr year_month_weekday
956	operator/(const month_weekday& __mwd, const year& __y) noexcept;
957
958	friend constexpr year_month_weekday_last
959	operator/(const year& __y, const month_weekday_last& __mwdl) noexcept;
960
961	friend constexpr year_month_weekday_last
962	operator/(const month_weekday_last& __mwdl, const year& __y) noexcept;
963	};
964
965	// WEEKDAY
966
967	class weekday
968	{
969	private:
970	unsigned char _M_wd;
971
972	static constexpr weekday
973	_S_from_days(const days& __d)
974	{
975	return weekday{__detail::__add_modulo<7>(4, __d.count())};
976	}
977
978	public:
979	weekday() = default;
980
981	explicit constexpr
982	weekday(unsigned __wd) noexcept
983	: _M_wd(__wd == 7 ? 0 : __wd) // __wd % 7 ?
984	{ }
985
986	constexpr
987	weekday(const sys_days& __dp) noexcept
988	: weekday{_S_from_days(__dp.time_since_epoch())}
989	{ }
990
991	explicit constexpr
992	weekday(const local_days& __dp) noexcept
993	: weekday{sys_days{__dp.time_since_epoch()}}
994	{ }
995
996	constexpr weekday&
997	operator++() noexcept
998	{
999	*this += days{1};
1000	return *this;
1001	}
1002
1003	constexpr weekday
1004	operator++(int) noexcept
1005	{
1006	auto __ret = *this;
1007	++(*this);
1008	return __ret;
1009	}
1010
1011	constexpr weekday&
1012	operator--() noexcept
1013	{
1014	*this -= days{1};
1015	return *this;
1016	}
1017
1018	constexpr weekday
1019	operator--(int) noexcept
1020	{
1021	auto __ret = *this;
1022	--(*this);
1023	return __ret;
1024	}
1025
1026	constexpr weekday&
1027	operator+=(const days& __d) noexcept
1028	{
1029	*this = *this + __d;
1030	return *this;
1031	}
1032
1033	constexpr weekday&
1034	operator-=(const days& __d) noexcept
1035	{
1036	*this = *this - __d;
1037	return *this;
1038	}
1039
1040	constexpr unsigned
1041	c_encoding() const noexcept
1042	{ return _M_wd; }
1043
1044	constexpr unsigned
1045	iso_encoding() const noexcept
1046	{ return _M_wd == 0u ? 7u : _M_wd; }
1047
1048	constexpr bool
1049	ok() const noexcept
1050	{ return _M_wd <= 6; }
1051
1052	constexpr weekday_indexed
1053	operator[](unsigned __index) const noexcept;
1054
1055	constexpr weekday_last
1056	operator[](last_spec) const noexcept;
1057
1058	friend constexpr bool
1059	operator==(const weekday& __x, const weekday& __y) noexcept
1060	{ return __x._M_wd == __y._M_wd; }
1061
1062	friend constexpr weekday
1063	operator+(const weekday& __x, const days& __y) noexcept
1064	{
1065	return weekday{__detail::__add_modulo<7>(__x._M_wd, __y.count())};
1066	}
1067
1068	friend constexpr weekday
1069	operator+(const days& __x, const weekday& __y) noexcept
1070	{ return __y + __x; }
1071
1072	friend constexpr weekday
1073	operator-(const weekday& __x, const days& __y) noexcept
1074	{
1075	return weekday{__detail::__sub_modulo<7>(__x._M_wd, __y.count())};
1076	}
1077
1078	friend constexpr days
1079	operator-(const weekday& __x, const weekday& __y) noexcept
1080	{
1081	const auto __n = __x.c_encoding() - __y.c_encoding();
1082	return static_cast<int>(__n) >= 0 ? days{__n} : days{__n + 7};
1083	}
1084	};
1085
1086	inline constexpr weekday Sunday{0};
1087	inline constexpr weekday Monday{1};
1088	inline constexpr weekday Tuesday{2};
1089	inline constexpr weekday Wednesday{3};
1090	inline constexpr weekday Thursday{4};
1091	inline constexpr weekday Friday{5};
1092	inline constexpr weekday Saturday{6};
1093
1094	// WEEKDAY_INDEXED
1095
1096	class weekday_indexed
1097	{
1098	private:
1099	chrono::weekday _M_wd;
1100	unsigned char _M_index;
1101
1102	public:
1103	weekday_indexed() = default;
1104
1105	constexpr
1106	weekday_indexed(const chrono::weekday& __wd, unsigned __index) noexcept
1107	: _M_wd(__wd), _M_index(__index)
1108	{ }
1109
1110	constexpr chrono::weekday
1111	weekday() const noexcept
1112	{ return _M_wd; }
1113
1114	constexpr unsigned
1115	index() const noexcept
1116	{ return _M_index; };
1117
1118	constexpr bool
1119	ok() const noexcept
1120	{ return _M_wd.ok() && 1 <= _M_index && _M_index <= 5; }
1121
1122	friend constexpr bool
1123	operator==(const weekday_indexed& __x, const weekday_indexed& __y) noexcept
1124	{ return __x.weekday() == __y.weekday() && __x.index() == __y.index(); }
1125
1126	friend constexpr month_weekday
1127	operator/(const month& __m, const weekday_indexed& __wdi) noexcept;
1128
1129	friend constexpr month_weekday
1130	operator/(int __m, const weekday_indexed& __wdi) noexcept;
1131
1132	friend constexpr month_weekday
1133	operator/(const weekday_indexed& __wdi, const month& __m) noexcept;
1134
1135	friend constexpr month_weekday
1136	operator/(const weekday_indexed& __wdi, int __m) noexcept;
1137
1138	friend constexpr year_month_weekday
1139	operator/(const year_month& __ym, const weekday_indexed& __wdi) noexcept;
1140	};
1141
1142	constexpr weekday_indexed
1143	weekday::operator[](unsigned __index) const noexcept
1144	{ return {*this, __index}; }
1145
1146	// WEEKDAY_LAST
1147
1148	class weekday_last
1149	{
1150	private:
1151	chrono::weekday _M_wd;
1152
1153	public:
1154	explicit constexpr
1155	weekday_last(const chrono::weekday& __wd) noexcept
1156	: _M_wd{__wd}
1157	{ }
1158
1159	constexpr chrono::weekday
1160	weekday() const noexcept
1161	{ return _M_wd; }
1162
1163	constexpr bool
1164	ok() const noexcept
1165	{ return _M_wd.ok(); }
1166
1167	friend constexpr bool
1168	operator==(const weekday_last& __x, const weekday_last& __y) noexcept
1169	{ return __x.weekday() == __y.weekday(); }
1170
1171	friend constexpr month_weekday_last
1172	operator/(int __m, const weekday_last& __wdl) noexcept;
1173
1174	friend constexpr month_weekday_last
1175	operator/(const weekday_last& __wdl, int __m) noexcept;
1176
1177	friend constexpr year_month_weekday_last
1178	operator/(const year_month& __ym, const weekday_last& __wdl) noexcept;
1179	};
1180
1181	constexpr weekday_last
1182	weekday::operator[](last_spec) const noexcept
1183	{ return weekday_last{*this}; }
1184
1185	// MONTH_DAY
1186
1187	class month_day
1188	{
1189	private:
1190	chrono::month _M_m;
1191	chrono::day _M_d;
1192
1193	public:
1194	month_day() = default;
1195
1196	constexpr
1197	month_day(const chrono::month& __m, const chrono::day& __d) noexcept
1198	: _M_m{__m}, _M_d{__d}
1199	{ }
1200
1201	constexpr chrono::month
1202	month() const noexcept
1203	{ return _M_m; }
1204
1205	constexpr chrono::day
1206	day() const noexcept
1207	{ return _M_d; }
1208
1209	constexpr bool
1210	ok() const noexcept
1211	{
1212	return _M_m.ok()
1213	&& 1u <= unsigned(_M_d)
1214	&& unsigned(_M_d) <= __detail::__days_per_month[unsigned(_M_m) - 1];
1215	}
1216
1217	friend constexpr bool
1218	operator==(const month_day& __x, const month_day& __y) noexcept
1219	{ return __x.month() == __y.month() && __x.day() == __y.day(); }
1220
1221	friend constexpr strong_ordering
1222	operator<=>(const month_day& __x, const month_day& __y) noexcept
1223	= default;
1224
1225	friend constexpr month_day
1226	operator/(const chrono::month& __m, const chrono::day& __d) noexcept
1227	{ return {__m, __d}; }
1228
1229	friend constexpr month_day
1230	operator/(const chrono::month& __m, int __d) noexcept
1231	{ return {__m, chrono::day(unsigned(__d))}; }
1232
1233	friend constexpr month_day
1234	operator/(int __m, const chrono::day& __d) noexcept
1235	{ return {chrono::month(unsigned(__m)), __d}; }
1236
1237	friend constexpr month_day
1238	operator/(const chrono::day& __d, const chrono::month& __m) noexcept
1239	{ return {__m, __d}; }
1240
1241	friend constexpr month_day
1242	operator/(const chrono::day& __d, int __m) noexcept
1243	{ return {chrono::month(unsigned(__m)), __d}; }
1244
1245	friend constexpr year_month_day
1246	operator/(int __y, const month_day& __md) noexcept;
1247
1248	friend constexpr year_month_day
1249	operator/(const month_day& __md, int __y) noexcept;
1250	};
1251
1252	// MONTH_DAY_LAST
1253
1254	class month_day_last
1255	{
1256	private:
1257	chrono::month _M_m;
1258
1259	public:
1260	explicit constexpr
1261	month_day_last(const chrono::month& __m) noexcept
1262	: _M_m{__m}
1263	{ }
1264
1265	constexpr chrono::month
1266	month() const noexcept
1267	{ return _M_m; }
1268
1269	constexpr bool
1270	ok() const noexcept
1271	{ return _M_m.ok(); }
1272
1273	friend constexpr bool
1274	operator==(const month_day_last& __x, const month_day_last& __y) noexcept
1275	{ return __x.month() == __y.month(); }
1276
1277	friend constexpr strong_ordering
1278	operator<=>(const month_day_last& __x, const month_day_last& __y) noexcept
1279	= default;
1280
1281	friend constexpr month_day_last
1282	operator/(const chrono::month& __m, last_spec) noexcept
1283	{ return month_day_last{__m}; }
1284
1285	friend constexpr month_day_last
1286	operator/(int __m, last_spec) noexcept
1287	{ return chrono::month(unsigned(__m)) / last; }
1288
1289	friend constexpr month_day_last
1290	operator/(last_spec, const chrono::month& __m) noexcept
1291	{ return __m / last; }
1292
1293	friend constexpr month_day_last
1294	operator/(last_spec, int __m) noexcept
1295	{ return __m / last; }
1296
1297	friend constexpr year_month_day_last
1298	operator/(int __y, const month_day_last& __mdl) noexcept;
1299
1300	friend constexpr year_month_day_last
1301	operator/(const month_day_last& __mdl, int __y) noexcept;
1302	};
1303
1304	// MONTH_WEEKDAY
1305
1306	class month_weekday
1307	{
1308	private:
1309	chrono::month _M_m;
1310	chrono::weekday_indexed _M_wdi;
1311
1312	public:
1313	constexpr
1314	month_weekday(const chrono::month& __m,
1315	const chrono::weekday_indexed& __wdi) noexcept
1316	: _M_m{__m}, _M_wdi{__wdi}
1317	{ }
1318
1319	constexpr chrono::month
1320	month() const noexcept
1321	{ return _M_m; }
1322
1323	constexpr chrono::weekday_indexed
1324	weekday_indexed() const noexcept
1325	{ return _M_wdi; }
1326
1327	constexpr bool
1328	ok() const noexcept
1329	{ return _M_m.ok() && _M_wdi.ok(); }
1330
1331	friend constexpr bool
1332	operator==(const month_weekday& __x, const month_weekday& __y) noexcept
1333	{
1334	return __x.month() == __y.month()
1335	&& __x.weekday_indexed() == __y.weekday_indexed();
1336	}
1337
1338	friend constexpr month_weekday
1339	operator/(const chrono::month& __m,
1340	const chrono::weekday_indexed& __wdi) noexcept
1341	{ return {__m, __wdi}; }
1342
1343	friend constexpr month_weekday
1344	operator/(int __m, const chrono::weekday_indexed& __wdi) noexcept
1345	{ return chrono::month(unsigned(__m)) / __wdi; }
1346
1347	friend constexpr month_weekday
1348	operator/(const chrono::weekday_indexed& __wdi,
1349	const chrono::month& __m) noexcept
1350	{ return __m / __wdi; }
1351
1352	friend constexpr month_weekday
1353	operator/(const chrono::weekday_indexed& __wdi, int __m) noexcept
1354	{ return __m / __wdi; }
1355
1356	friend constexpr year_month_weekday
1357	operator/(int __y, const month_weekday& __mwd) noexcept;
1358
1359	friend constexpr year_month_weekday
1360	operator/(const month_weekday& __mwd, int __y) noexcept;
1361	};
1362
1363	// MONTH_WEEKDAY_LAST
1364
1365	class month_weekday_last
1366	{
1367	private:
1368	chrono::month _M_m;
1369	chrono::weekday_last _M_wdl;
1370
1371	public:
1372	constexpr
1373	month_weekday_last(const chrono::month& __m,
1374	const chrono::weekday_last& __wdl) noexcept
1375	:_M_m{__m}, _M_wdl{__wdl}
1376	{ }
1377
1378	constexpr chrono::month
1379	month() const noexcept
1380	{ return _M_m; }
1381
1382	constexpr chrono::weekday_last
1383	weekday_last() const noexcept
1384	{ return _M_wdl; }
1385
1386	constexpr bool
1387	ok() const noexcept
1388	{ return _M_m.ok() && _M_wdl.ok(); }
1389
1390	friend constexpr bool
1391	operator==(const month_weekday_last& __x,
1392	const month_weekday_last& __y) noexcept
1393	{
1394	return __x.month() == __y.month()
1395	&& __x.weekday_last() == __y.weekday_last();
1396	}
1397
1398	friend constexpr month_weekday_last
1399	operator/(const chrono::month& __m,
1400	const chrono::weekday_last& __wdl) noexcept
1401	{ return {__m, __wdl}; }
1402
1403	friend constexpr month_weekday_last
1404	operator/(int __m, const chrono::weekday_last& __wdl) noexcept
1405	{ return chrono::month(unsigned(__m)) / __wdl; }
1406
1407	friend constexpr month_weekday_last
1408	operator/(const chrono::weekday_last& __wdl,
1409	const chrono::month& __m) noexcept
1410	{ return __m / __wdl; }
1411
1412	friend constexpr month_weekday_last
1413	operator/(const chrono::weekday_last& __wdl, int __m) noexcept
1414	{ return chrono::month(unsigned(__m)) / __wdl; }
1415
1416	friend constexpr year_month_weekday_last
1417	operator/(int __y, const month_weekday_last& __mwdl) noexcept;
1418
1419	friend constexpr year_month_weekday_last
1420	operator/(const month_weekday_last& __mwdl, int __y) noexcept;
1421	};
1422
1423	// YEAR_MONTH
1424
1425	namespace __detail
1426	{
1427	// [time.cal.ym], [time.cal.ymd], etc constrain the 'months'-based
1428	// addition/subtraction operator overloads like so:
1429	//
1430	// Constraints: if the argument supplied by the caller for the months
1431	// parameter is convertible to years, its implicit conversion sequence
1432	// to years is worse than its implicit conversion sequence to months.
1433	//
1434	// We realize this constraint by templatizing the 'months'-based
1435	// overloads (using a dummy defaulted template parameter), so that
1436	// overload resolution doesn't select the 'months'-based overload unless
1437	// the implicit conversion sequence to 'months' is better than that to
1438	// 'years'.
1439	using __months_years_conversion_disambiguator = void;
1440	}
1441
1442	class year_month
1443	{
1444	private:
1445	chrono::year _M_y;
1446	chrono::month _M_m;
1447
1448	public:
1449	year_month() = default;
1450
1451	constexpr
1452	year_month(const chrono::year& __y, const chrono::month& __m) noexcept
1453	: _M_y{__y}, _M_m{__m}
1454	{ }
1455
1456	constexpr chrono::year
1457	year() const noexcept
1458	{ return _M_y; }
1459
1460	constexpr chrono::month
1461	month() const noexcept
1462	{ return _M_m; }
1463
1464	template<typename = __detail::__months_years_conversion_disambiguator>
1465	constexpr year_month&
1466	operator+=(const months& __dm) noexcept
1467	{
1468	*this = *this + __dm;
1469	return *this;
1470	}
1471
1472	template<typename = __detail::__months_years_conversion_disambiguator>
1473	constexpr year_month&
1474	operator-=(const months& __dm) noexcept
1475	{
1476	*this = *this - __dm;
1477	return *this;
1478	}
1479
1480	constexpr year_month&
1481	operator+=(const years& __dy) noexcept
1482	{
1483	*this = *this + __dy;
1484	return *this;
1485	}
1486
1487	constexpr year_month&
1488	operator-=(const years& __dy) noexcept
1489	{
1490	*this = *this - __dy;
1491	return *this;
1492	}
1493
1494	constexpr bool
1495	ok() const noexcept
1496	{ return _M_y.ok() && _M_m.ok(); }
1497
1498	friend constexpr bool
1499	operator==(const year_month& __x, const year_month& __y) noexcept
1500	{ return __x.year() == __y.year() && __x.month() == __y.month(); }
1501
1502	friend constexpr strong_ordering
1503	operator<=>(const year_month& __x, const year_month& __y) noexcept
1504	= default;
1505
1506	template<typename = __detail::__months_years_conversion_disambiguator>
1507	friend constexpr year_month
1508	operator+(const year_month& __ym, const months& __dm) noexcept
1509	{
1510	// TODO: Optimize?
1511	auto __m = __ym.month() + __dm;
1512	auto __i = int(unsigned(__ym.month())) - 1 + __dm.count();
1513	auto __y = (__i < 0
1514	? __ym.year() + years{(__i - 11) / 12}
1515	: __ym.year() + years{__i / 12});
1516	return __y / __m;
1517	}
1518
1519	template<typename = __detail::__months_years_conversion_disambiguator>
1520	friend constexpr year_month
1521	operator+(const months& __dm, const year_month& __ym) noexcept
1522	{ return __ym + __dm; }
1523
1524	template<typename = __detail::__months_years_conversion_disambiguator>
1525	friend constexpr year_month
1526	operator-(const year_month& __ym, const months& __dm) noexcept
1527	{ return __ym + -__dm; }
1528
1529	friend constexpr months
1530	operator-(const year_month& __x, const year_month& __y) noexcept
1531	{
1532	return (__x.year() - __y.year()
1533	+ months{static_cast<int>(unsigned{__x.month()})
1534	- static_cast<int>(unsigned{__y.month()})});
1535	}
1536
1537	friend constexpr year_month
1538	operator+(const year_month& __ym, const years& __dy) noexcept
1539	{ return (__ym.year() + __dy) / __ym.month(); }
1540
1541	friend constexpr year_month
1542	operator+(const years& __dy, const year_month& __ym) noexcept
1543	{ return __ym + __dy; }
1544
1545	friend constexpr year_month
1546	operator-(const year_month& __ym, const years& __dy) noexcept
1547	{ return __ym + -__dy; }
1548
1549	friend constexpr year_month
1550	operator/(const chrono::year& __y, const chrono::month& __m) noexcept
1551	{ return {__y, __m}; }
1552
1553	friend constexpr year_month
1554	operator/(const chrono::year& __y, int __m) noexcept
1555	{ return {__y, chrono::month(unsigned(__m))}; }
1556
1557	friend constexpr year_month_day
1558	operator/(const year_month& __ym, int __d) noexcept;
1559
1560	friend constexpr year_month_day_last
1561	operator/(const year_month& __ym, last_spec) noexcept;
1562	};
1563
1564	// YEAR_MONTH_DAY
1565
1566	class year_month_day
1567	{
1568	private:
1569	chrono::year _M_y;
1570	chrono::month _M_m;
1571	chrono::day _M_d;
1572
1573	static constexpr year_month_day _S_from_days(const days& __dp) noexcept;
1574
1575	constexpr days _M_days_since_epoch() const noexcept;
1576
1577	public:
1578	year_month_day() = default;
1579
1580	constexpr
1581	year_month_day(const chrono::year& __y, const chrono::month& __m,
1582	const chrono::day& __d) noexcept
1583	: _M_y{__y}, _M_m{__m}, _M_d{__d}
1584	{ }
1585
1586	constexpr
1587	year_month_day(const year_month_day_last& __ymdl) noexcept;
1588
1589	constexpr
1590	year_month_day(const sys_days& __dp) noexcept
1591	: year_month_day(_S_from_days(__dp.time_since_epoch()))
1592	{ }
1593
1594	explicit constexpr
1595	year_month_day(const local_days& __dp) noexcept
1596	: year_month_day(sys_days{__dp.time_since_epoch()})
1597	{ }
1598
1599	template<typename = __detail::__months_years_conversion_disambiguator>
1600	constexpr year_month_day&
1601	operator+=(const months& __m) noexcept
1602	{
1603	*this = *this + __m;
1604	return *this;
1605	}
1606
1607	template<typename = __detail::__months_years_conversion_disambiguator>
1608	constexpr year_month_day&
1609	operator-=(const months& __m) noexcept
1610	{
1611	*this = *this - __m;
1612	return *this;
1613	}
1614
1615	constexpr year_month_day&
1616	operator+=(const years& __y) noexcept
1617	{
1618	*this = *this + __y;
1619	return *this;
1620	}
1621
1622	constexpr year_month_day&
1623	operator-=(const years& __y) noexcept
1624	{
1625	*this = *this - __y;
1626	return *this;
1627	}
1628
1629	constexpr chrono::year
1630	year() const noexcept
1631	{ return _M_y; }
1632
1633	constexpr chrono::month
1634	month() const noexcept
1635	{ return _M_m; }
1636
1637	constexpr chrono::day
1638	day() const noexcept
1639	{ return _M_d; }
1640
1641	constexpr
1642	operator sys_days() const noexcept
1643	{ return sys_days{_M_days_since_epoch()}; }
1644
1645	explicit constexpr
1646	operator local_days() const noexcept
1647	{ return local_days{sys_days{*this}.time_since_epoch()}; }
1648
1649	constexpr bool ok() const noexcept;
1650
1651	friend constexpr bool
1652	operator==(const year_month_day& __x, const year_month_day& __y) noexcept
1653	{
1654	return __x.year() == __y.year()
1655	&& __x.month() == __y.month()
1656	&& __x.day() == __y.day();
1657	}
1658
1659	friend constexpr strong_ordering
1660	operator<=>(const year_month_day& __x, const year_month_day& __y) noexcept
1661	= default;
1662
1663	template<typename = __detail::__months_years_conversion_disambiguator>
1664	friend constexpr year_month_day
1665	operator+(const year_month_day& __ymd, const months& __dm) noexcept
1666	{ return (__ymd.year() / __ymd.month() + __dm) / __ymd.day(); }
1667
1668	template<typename = __detail::__months_years_conversion_disambiguator>
1669	friend constexpr year_month_day
1670	operator+(const months& __dm, const year_month_day& __ymd) noexcept
1671	{ return __ymd + __dm; }
1672
1673	friend constexpr year_month_day
1674	operator+(const year_month_day& __ymd, const years& __dy) noexcept
1675	{ return (__ymd.year() + __dy) / __ymd.month() / __ymd.day(); }
1676
1677	friend constexpr year_month_day
1678	operator+(const years& __dy, const year_month_day& __ymd) noexcept
1679	{ return __ymd + __dy; }
1680
1681	template<typename = __detail::__months_years_conversion_disambiguator>
1682	friend constexpr year_month_day
1683	operator-(const year_month_day& __ymd, const months& __dm) noexcept
1684	{ return __ymd + -__dm; }
1685
1686	friend constexpr year_month_day
1687	operator-(const year_month_day& __ymd, const years& __dy) noexcept
1688	{ return __ymd + -__dy; }
1689
1690	friend constexpr year_month_day
1691	operator/(const year_month& __ym, const chrono::day& __d) noexcept
1692	{ return {__ym.year(), __ym.month(), __d}; }
1693
1694	friend constexpr year_month_day
1695	operator/(const year_month& __ym, int __d) noexcept
1696	{ return __ym / chrono::day{unsigned(__d)}; }
1697
1698	friend constexpr year_month_day
1699	operator/(const chrono::year& __y, const month_day& __md) noexcept
1700	{ return __y / __md.month() / __md.day(); }
1701
1702	friend constexpr year_month_day
1703	operator/(int __y, const month_day& __md) noexcept
1704	{ return chrono::year{__y} / __md; }
1705
1706	friend constexpr year_month_day
1707	operator/(const month_day& __md, const chrono::year& __y) noexcept
1708	{ return __y / __md; }
1709
1710	friend constexpr year_month_day
1711	operator/(const month_day& __md, int __y) noexcept
1712	{ return chrono::year(__y) / __md; }
1713	};
1714
1715	// Construct from days since 1970/01/01.
1716	// Proposition 6.3 of Neri and Schneider,
1717	// "Euclidean Affine Functions and Applications to Calendar Algorithms".
1718	// https://arxiv.org/abs/2102.06959
1719	constexpr year_month_day
1720	year_month_day::_S_from_days(const days& __dp) noexcept
1721	{
1722	constexpr auto __z2 = static_cast<uint32_t>(-1468000);
1723	constexpr auto __r2_e3 = static_cast<uint32_t>(536895458);
1724
1725	const auto __r0 = static_cast<uint32_t>(__dp.count()) + __r2_e3;
1726
1727	const auto __n1 = 4 * __r0 + 3;
1728	const auto __q1 = __n1 / 146097;
1729	const auto __r1 = __n1 % 146097 / 4;
1730
1731	constexpr auto __p32 = static_cast<uint64_t>(1) << 32;
1732	const auto __n2 = 4 * __r1 + 3;
1733	const auto __u2 = static_cast<uint64_t>(2939745) * __n2;
1734	const auto __q2 = static_cast<uint32_t>(__u2 / __p32);
1735	const auto __r2 = static_cast<uint32_t>(__u2 % __p32) / 2939745 / 4;
1736
1737	constexpr auto __p16 = static_cast<uint32_t>(1) << 16;
1738	const auto __n3 = 2141 * __r2 + 197913;
1739	const auto __q3 = __n3 / __p16;
1740	const auto __r3 = __n3 % __p16 / 2141;
1741
1742	const auto __y0 = 100 * __q1 + __q2;
1743	const auto __m0 = __q3;
1744	const auto __d0 = __r3;
1745
1746	const auto __j = __r2 >= 306;
1747	const auto __y1 = __y0 + __j;
1748	const auto __m1 = __j ? __m0 - 12 : __m0;
1749	const auto __d1 = __d0 + 1;
1750
1751	return year_month_day{chrono::year{static_cast<int>(__y1 + __z2)},
1752	chrono::month{__m1}, chrono::day{__d1}};
1753	}
1754
1755	// Days since 1970/01/01.
1756	// Proposition 6.2 of Neri and Schneider,
1757	// "Euclidean Affine Functions and Applications to Calendar Algorithms".
1758	// https://arxiv.org/abs/2102.06959
1759	constexpr days
1760	year_month_day::_M_days_since_epoch() const noexcept
1761	{
1762	auto constexpr __z2 = static_cast<uint32_t>(-1468000);
1763	auto constexpr __r2_e3 = static_cast<uint32_t>(536895458);
1764
1765	const auto __y1 = static_cast<uint32_t>(static_cast<int>(_M_y)) - __z2;
1766	const auto __m1 = static_cast<uint32_t>(static_cast<unsigned>(_M_m));
1767	const auto __d1 = static_cast<uint32_t>(static_cast<unsigned>(_M_d));
1768
1769	const auto __j = static_cast<uint32_t>(__m1 < 3);
1770	const auto __y0 = __y1 - __j;
1771	const auto __m0 = __j ? __m1 + 12 : __m1;
1772	const auto __d0 = __d1 - 1;
1773
1774	const auto __q1 = __y0 / 100;
1775	const auto __yc = 1461 * __y0 / 4 - __q1 + __q1 / 4;
1776	const auto __mc = (979 *__m0 - 2919) / 32;
1777	const auto __dc = __d0;
1778
1779	return days{static_cast<int32_t>(__yc + __mc + __dc - __r2_e3)};
1780	}
1781
1782	// YEAR_MONTH_DAY_LAST
1783
1784	class year_month_day_last
1785	{
1786	private:
1787	chrono::year _M_y;
1788	chrono::month_day_last _M_mdl;
1789
1790	public:
1791	constexpr
1792	year_month_day_last(const chrono::year& __y,
1793	const chrono::month_day_last& __mdl) noexcept
1794	: _M_y{__y}, _M_mdl{__mdl}
1795	{ }
1796
1797	template<typename = __detail::__months_years_conversion_disambiguator>
1798	constexpr year_month_day_last&
1799	operator+=(const months& __m) noexcept
1800	{
1801	*this = *this + __m;
1802	return *this;
1803	}
1804
1805	template<typename = __detail::__months_years_conversion_disambiguator>
1806	constexpr year_month_day_last&
1807	operator-=(const months& __m) noexcept
1808	{
1809	*this = *this - __m;
1810	return *this;
1811	}
1812
1813	constexpr year_month_day_last&
1814	operator+=(const years& __y) noexcept
1815	{
1816	*this = *this + __y;
1817	return *this;
1818	}
1819
1820	constexpr year_month_day_last&
1821	operator-=(const years& __y) noexcept
1822	{
1823	*this = *this - __y;
1824	return *this;
1825	}
1826
1827	constexpr chrono::year
1828	year() const noexcept
1829	{ return _M_y; }
1830
1831	constexpr chrono::month
1832	month() const noexcept
1833	{ return _M_mdl.month(); }
1834
1835	constexpr chrono::month_day_last
1836	month_day_last() const noexcept
1837	{ return _M_mdl; }
1838
1839	// Return A day representing the last day of this year, month pair.
1840	constexpr chrono::day
1841	day() const noexcept
1842	{
1843	const auto __m = static_cast<unsigned>(month());
1844
1845	// The result is unspecified if __m < 1 or __m > 12. Hence, assume
1846	// 1 <= __m <= 12. For __m != 2, day() == 30 or day() == 31 or, in
1847	// other words, day () == 30 | b, where b is in {0, 1}.
1848
1849	// If __m in {1, 3, 4, 5, 6, 7}, then b is 1 if, and only if, __m is
1850	// odd. Hence, b = __m & 1 = (__m ^ 0) & 1.
1851
1852	// If __m in {8, 9, 10, 11, 12}, then b is 1 if, and only if, __m is
1853	// even. Hence, b = (__m ^ 1) & 1.
1854
1855	// Therefore, b = (__m ^ c) & 1, where c = 0, if __m < 8, or c = 1 if
1856	// __m >= 8, that is, c = __m >> 3.
1857
1858	// Since 30 = (11110)_2 and __m <= 31 = (11111)_2, the "& 1" in b's
1859	// calculation is unnecessary.
1860
1861	// The performance of this implementation does not depend on look-up
1862	// tables being on the L1 cache.
1863	return chrono::day{__m != 2 ? (__m ^ (__m >> 3)) | 30
1864	: _M_y.is_leap() ? 29 : 28};
1865	}
1866
1867	constexpr
1868	operator sys_days() const noexcept
1869	{ return sys_days{year() / month() / day()}; }
1870
1871	explicit constexpr
1872	operator local_days() const noexcept
1873	{ return local_days{sys_days{*this}.time_since_epoch()}; }
1874
1875	constexpr bool
1876	ok() const noexcept
1877	{ return _M_y.ok() && _M_mdl.ok(); }
1878
1879	friend constexpr bool
1880	operator==(const year_month_day_last& __x,
1881	const year_month_day_last& __y) noexcept
1882	{
1883	return __x.year() == __y.year()
1884	&& __x.month_day_last() == __y.month_day_last();
1885	}
1886
1887	friend constexpr strong_ordering
1888	operator<=>(const year_month_day_last& __x,
1889	const year_month_day_last& __y) noexcept
1890	= default;
1891
1892	template<typename = __detail::__months_years_conversion_disambiguator>
1893	friend constexpr year_month_day_last
1894	operator+(const year_month_day_last& __ymdl,
1895	const months& __dm) noexcept
1896	{ return (__ymdl.year() / __ymdl.month() + __dm) / last; }
1897
1898	template<typename = __detail::__months_years_conversion_disambiguator>
1899	friend constexpr year_month_day_last
1900	operator+(const months& __dm,
1901	const year_month_day_last& __ymdl) noexcept
1902	{ return __ymdl + __dm; }
1903
1904	template<typename = __detail::__months_years_conversion_disambiguator>
1905	friend constexpr year_month_day_last
1906	operator-(const year_month_day_last& __ymdl,
1907	const months& __dm) noexcept
1908	{ return __ymdl + -__dm; }
1909
1910	friend constexpr year_month_day_last
1911	operator+(const year_month_day_last& __ymdl,
1912	const years& __dy) noexcept
1913	{ return {__ymdl.year() + __dy, __ymdl.month_day_last()}; }
1914
1915	friend constexpr year_month_day_last
1916	operator+(const years& __dy,
1917	const year_month_day_last& __ymdl) noexcept
1918	{ return __ymdl + __dy; }
1919
1920	friend constexpr year_month_day_last
1921	operator-(const year_month_day_last& __ymdl,
1922	const years& __dy) noexcept
1923	{ return __ymdl + -__dy; }
1924
1925	friend constexpr year_month_day_last
1926	operator/(const year_month& __ym, last_spec) noexcept
1927	{ return {__ym.year(), chrono::month_day_last{__ym.month()}}; }
1928
1929	friend constexpr year_month_day_last
1930	operator/(const chrono::year& __y,
1931	const chrono::month_day_last& __mdl) noexcept
1932	{ return {__y, __mdl}; }
1933
1934	friend constexpr year_month_day_last
1935	operator/(int __y, const chrono::month_day_last& __mdl) noexcept
1936	{ return chrono::year(__y) / __mdl; }
1937
1938	friend constexpr year_month_day_last
1939	operator/(const chrono::month_day_last& __mdl,
1940	const chrono::year& __y) noexcept
1941	{ return __y / __mdl; }
1942
1943	friend constexpr year_month_day_last
1944	operator/(const chrono::month_day_last& __mdl, int __y) noexcept
1945	{ return chrono::year(__y) / __mdl; }
1946	};
1947
1948	// year_month_day ctor from year_month_day_last
1949	constexpr
1950	year_month_day::year_month_day(const year_month_day_last& __ymdl) noexcept
1951	: _M_y{__ymdl.year()}, _M_m{__ymdl.month()}, _M_d{__ymdl.day()}
1952	{ }
1953
1954	constexpr bool
1955	year_month_day::ok() const noexcept
1956	{
1957	if (!_M_y.ok() || !_M_m.ok())
1958	return false;
1959	return chrono::day{1} <= _M_d && _M_d <= (_M_y / _M_m / last).day();
1960	}
1961
1962	// YEAR_MONTH_WEEKDAY
1963
1964	class year_month_weekday
1965	{
1966	private:
1967	chrono::year _M_y;
1968	chrono::month _M_m;
1969	chrono::weekday_indexed _M_wdi;
1970
1971	static constexpr year_month_weekday
1972	_S_from_sys_days(const sys_days& __dp)
1973	{
1974	year_month_day __ymd{__dp};
1975	chrono::weekday __wd{__dp};
1976	auto __index = __wd[(unsigned{__ymd.day()} - 1) / 7 + 1];
1977	return {__ymd.year(), __ymd.month(), __index};
1978	}
1979
1980	public:
1981	year_month_weekday() = default;
1982
1983	constexpr
1984	year_month_weekday(const chrono::year& __y, const chrono::month& __m,
1985	const chrono::weekday_indexed& __wdi) noexcept
1986	: _M_y{__y}, _M_m{__m}, _M_wdi{__wdi}
1987	{ }
1988
1989	constexpr
1990	year_month_weekday(const sys_days& __dp) noexcept
1991	: year_month_weekday{_S_from_sys_days(__dp)}
1992	{ }
1993
1994	explicit constexpr
1995	year_month_weekday(const local_days& __dp) noexcept
1996	: year_month_weekday{sys_days{__dp.time_since_epoch()}}
1997	{ }
1998
1999	template<typename = __detail::__months_years_conversion_disambiguator>
2000	constexpr year_month_weekday&
2001	operator+=(const months& __m) noexcept
2002	{
2003	*this = *this + __m;
2004	return *this;
2005	}
2006
2007	template<typename = __detail::__months_years_conversion_disambiguator>
2008	constexpr year_month_weekday&
2009	operator-=(const months& __m) noexcept
2010	{
2011	*this = *this - __m;
2012	return *this;
2013	}
2014
2015	constexpr year_month_weekday&
2016	operator+=(const years& __y) noexcept
2017	{
2018	*this = *this + __y;
2019	return *this;
2020	}
2021
2022	constexpr year_month_weekday&
2023	operator-=(const years& __y) noexcept
2024	{
2025	*this = *this - __y;
2026	return *this;
2027	}
2028
2029	constexpr chrono::year
2030	year() const noexcept
2031	{ return _M_y; }
2032
2033	constexpr chrono::month
2034	month() const noexcept
2035	{ return _M_m; }
2036
2037	constexpr chrono::weekday
2038	weekday() const noexcept
2039	{ return _M_wdi.weekday(); }
2040
2041	constexpr unsigned
2042	index() const noexcept
2043	{ return _M_wdi.index(); }
2044
2045	constexpr chrono::weekday_indexed
2046	weekday_indexed() const noexcept
2047	{ return _M_wdi; }
2048
2049	constexpr
2050	operator sys_days() const noexcept
2051	{
2052	auto __d = sys_days{year() / month() / 1};
2053	return __d + (weekday() - chrono::weekday(__d)
2054	+ days{(static_cast<int>(index())-1)*7});
2055	}
2056
2057	explicit constexpr
2058	operator local_days() const noexcept
2059	{ return local_days{sys_days{*this}.time_since_epoch()}; }
2060
2061	constexpr bool
2062	ok() const noexcept
2063	{
2064	if (!_M_y.ok() || !_M_m.ok() || !_M_wdi.ok())
2065	return false;
2066	if (_M_wdi.index() <= 4)
2067	return true;
2068	days __d = (_M_wdi.weekday()
2069	- chrono::weekday{sys_days{_M_y / _M_m / 1}}
2070	+ days((_M_wdi.index()-1)*7 + 1));
2071	__glibcxx_assert(__d.count() >= 1);
2072	return (unsigned)__d.count() <= (unsigned)(_M_y / _M_m / last).day();
2073	}
2074
2075	friend constexpr bool
2076	operator==(const year_month_weekday& __x,
2077	const year_month_weekday& __y) noexcept
2078	{
2079	return __x.year() == __y.year()
2080	&& __x.month() == __y.month()
2081	&& __x.weekday_indexed() == __y.weekday_indexed();
2082	}
2083
2084	template<typename = __detail::__months_years_conversion_disambiguator>
2085	friend constexpr year_month_weekday
2086	operator+(const year_month_weekday& __ymwd, const months& __dm) noexcept
2087	{
2088	return ((__ymwd.year() / __ymwd.month() + __dm)
2089	/ __ymwd.weekday_indexed());
2090	}
2091
2092	template<typename = __detail::__months_years_conversion_disambiguator>
2093	friend constexpr year_month_weekday
2094	operator+(const months& __dm, const year_month_weekday& __ymwd) noexcept
2095	{ return __ymwd + __dm; }
2096
2097	friend constexpr year_month_weekday
2098	operator+(const year_month_weekday& __ymwd, const years& __dy) noexcept
2099	{ return {__ymwd.year() + __dy, __ymwd.month(), __ymwd.weekday_indexed()}; }
2100
2101	friend constexpr year_month_weekday
2102	operator+(const years& __dy, const year_month_weekday& __ymwd) noexcept
2103	{ return __ymwd + __dy; }
2104
2105	template<typename = __detail::__months_years_conversion_disambiguator>
2106	friend constexpr year_month_weekday
2107	operator-(const year_month_weekday& __ymwd, const months& __dm) noexcept
2108	{ return __ymwd + -__dm; }
2109
2110	friend constexpr year_month_weekday
2111	operator-(const year_month_weekday& __ymwd, const years& __dy) noexcept
2112	{ return __ymwd + -__dy; }
2113
2114	friend constexpr year_month_weekday
2115	operator/(const year_month& __ym,
2116	const chrono::weekday_indexed& __wdi) noexcept
2117	{ return {__ym.year(), __ym.month(), __wdi}; }
2118
2119	friend constexpr year_month_weekday
2120	operator/(const chrono::year& __y, const month_weekday& __mwd) noexcept
2121	{ return {__y, __mwd.month(), __mwd.weekday_indexed()}; }
2122
2123	friend constexpr year_month_weekday
2124	operator/(int __y, const month_weekday& __mwd) noexcept
2125	{ return chrono::year(__y) / __mwd; }
2126
2127	friend constexpr year_month_weekday
2128	operator/(const month_weekday& __mwd, const chrono::year& __y) noexcept
2129	{ return __y / __mwd; }
2130
2131	friend constexpr year_month_weekday
2132	operator/(const month_weekday& __mwd, int __y) noexcept
2133	{ return chrono::year(__y) / __mwd; }
2134	};
2135
2136	// YEAR_MONTH_WEEKDAY_LAST
2137
2138	class year_month_weekday_last
2139	{
2140	private:
2141	chrono::year _M_y;
2142	chrono::month _M_m;
2143	chrono::weekday_last _M_wdl;
2144
2145	public:
2146	constexpr
2147	year_month_weekday_last(const chrono::year& __y, const chrono::month& __m,
2148	const chrono::weekday_last& __wdl) noexcept
2149	: _M_y{__y}, _M_m{__m}, _M_wdl{__wdl}
2150	{ }
2151
2152	template<typename = __detail::__months_years_conversion_disambiguator>
2153	constexpr year_month_weekday_last&
2154	operator+=(const months& __m) noexcept
2155	{
2156	*this = *this + __m;
2157	return *this;
2158	}
2159
2160	template<typename = __detail::__months_years_conversion_disambiguator>
2161	constexpr year_month_weekday_last&
2162	operator-=(const months& __m) noexcept
2163	{
2164	*this = *this - __m;
2165	return *this;
2166	}
2167
2168	constexpr year_month_weekday_last&
2169	operator+=(const years& __y) noexcept
2170	{
2171	*this = *this + __y;
2172	return *this;
2173	}
2174
2175	constexpr year_month_weekday_last&
2176	operator-=(const years& __y) noexcept
2177	{
2178	*this = *this - __y;
2179	return *this;
2180	}
2181
2182	constexpr chrono::year
2183	year() const noexcept
2184	{ return _M_y; }
2185
2186	constexpr chrono::month
2187	month() const noexcept
2188	{ return _M_m; }
2189
2190	constexpr chrono::weekday
2191	weekday() const noexcept
2192	{ return _M_wdl.weekday(); }
2193
2194	constexpr chrono::weekday_last
2195	weekday_last() const noexcept
2196	{ return _M_wdl; }
2197
2198	constexpr
2199	operator sys_days() const noexcept
2200	{
2201	const auto __d = sys_days{_M_y / _M_m / last};
2202	return sys_days{(__d - (chrono::weekday{__d}
2203	- _M_wdl.weekday())).time_since_epoch()};
2204	}
2205
2206	explicit constexpr
2207	operator local_days() const noexcept
2208	{ return local_days{sys_days{*this}.time_since_epoch()}; }
2209
2210	constexpr bool
2211	ok() const noexcept
2212	{ return _M_y.ok() && _M_m.ok() && _M_wdl.ok(); }
2213
2214	friend constexpr bool
2215	operator==(const year_month_weekday_last& __x,
2216	const year_month_weekday_last& __y) noexcept
2217	{
2218	return __x.year() == __y.year()
2219	&& __x.month() == __y.month()
2220	&& __x.weekday_last() == __y.weekday_last();
2221	}
2222
2223	template<typename = __detail::__months_years_conversion_disambiguator>
2224	friend constexpr year_month_weekday_last
2225	operator+(const year_month_weekday_last& __ymwdl,
2226	const months& __dm) noexcept
2227	{
2228	return ((__ymwdl.year() / __ymwdl.month() + __dm)
2229	/ __ymwdl.weekday_last());
2230	}
2231
2232	template<typename = __detail::__months_years_conversion_disambiguator>
2233	friend constexpr year_month_weekday_last
2234	operator+(const months& __dm,
2235	const year_month_weekday_last& __ymwdl) noexcept
2236	{ return __ymwdl + __dm; }
2237
2238	friend constexpr year_month_weekday_last
2239	operator+(const year_month_weekday_last& __ymwdl,
2240	const years& __dy) noexcept
2241	{ return {__ymwdl.year() + __dy, __ymwdl.month(), __ymwdl.weekday_last()}; }
2242
2243	friend constexpr year_month_weekday_last
2244	operator+(const years& __dy,
2245	const year_month_weekday_last& __ymwdl) noexcept
2246	{ return __ymwdl + __dy; }
2247
2248	template<typename = __detail::__months_years_conversion_disambiguator>
2249	friend constexpr year_month_weekday_last
2250	operator-(const year_month_weekday_last& __ymwdl,
2251	const months& __dm) noexcept
2252	{ return __ymwdl + -__dm; }
2253
2254	friend constexpr year_month_weekday_last
2255	operator-(const year_month_weekday_last& __ymwdl,
2256	const years& __dy) noexcept
2257	{ return __ymwdl + -__dy; }
2258
2259	friend constexpr year_month_weekday_last
2260	operator/(const year_month& __ym,
2261	const chrono::weekday_last& __wdl) noexcept
2262	{ return {__ym.year(), __ym.month(), __wdl}; }
2263
2264	friend constexpr year_month_weekday_last
2265	operator/(const chrono::year& __y,
2266	const chrono::month_weekday_last& __mwdl) noexcept
2267	{ return {__y, __mwdl.month(), __mwdl.weekday_last()}; }
2268
2269	friend constexpr year_month_weekday_last
2270	operator/(int __y, const chrono::month_weekday_last& __mwdl) noexcept
2271	{ return chrono::year(__y) / __mwdl; }
2272
2273	friend constexpr year_month_weekday_last
2274	operator/(const chrono::month_weekday_last& __mwdl,
2275	const chrono::year& __y) noexcept
2276	{ return __y / __mwdl; }
2277
2278	friend constexpr year_month_weekday_last
2279	operator/(const chrono::month_weekday_last& __mwdl, int __y) noexcept
2280	{ return chrono::year(__y) / __mwdl; }
2281	};
2282
2283	// HH_MM_SS
2284
2285	/// @cond undocumented
2286	namespace __detail
2287	{
2288	consteval long long
2289	__pow10(unsigned __n)
2290	{
2291	long long __r = 1;
2292	while (__n-- > 0)
2293	__r *= 10;
2294	return __r;
2295	}
2296
2297	template<typename _Duration> struct __utc_leap_second;
2298	}
2299	/// @endcond
2300
2301	/** Utility for splitting a duration into hours, minutes, and seconds
2302	*
2303	* This is a convenience type that provides accessors for the constituent
2304	* parts (hours, minutes, seconds and subseconds) of a duration.
2305	*
2306	* @since C++20
2307	*/
2308	template<typename _Duration>
2309	class hh_mm_ss
2310	{
2311	static_assert( __is_duration<_Duration>::value );
2312
2313	private:
2314	static consteval int
2315	_S_fractional_width()
2316	{
2317	auto __den = _Duration::period::den;
2318	const int __multiplicity_2 = std::__countr_zero((uintmax_t)__den);
2319	__den >>= __multiplicity_2;
2320	int __multiplicity_5 = 0;
2321	while ((__den % 5) == 0)
2322	{
2323	++__multiplicity_5;
2324	__den /= 5;
2325	}
2326	if (__den != 1)
2327	return 6;
2328
2329	int __width = (__multiplicity_2 > __multiplicity_5
2330	? __multiplicity_2 : __multiplicity_5);
2331	if (__width > 18)
2332	__width = 18;
2333	return __width;
2334	}
2335
2336	constexpr
2337	hh_mm_ss(_Duration __d, bool __is_neg)
2338	: _M_h (duration_cast<chrono::hours>(__d)),
2339	_M_m (duration_cast<chrono::minutes>(__d - hours())),
2340	_M_s (duration_cast<chrono::seconds>(__d - hours() - minutes())),
2341	_M_is_neg(__is_neg)
2342	{
2343	auto __ss = __d - hours() - minutes() - seconds();
2344	if constexpr (treat_as_floating_point_v<typename precision::rep>)
2345	_M_ss._M_r = __ss.count();
2346	else if constexpr (precision::period::den != 1)
2347	_M_ss._M_r = duration_cast<precision>(__ss).count();
2348	}
2349
2350	static constexpr _Duration
2351	_S_abs(_Duration __d)
2352	{
2353	if constexpr (numeric_limits<typename _Duration::rep>::is_signed)
2354	return chrono::abs(__d);
2355	else
2356	return __d;
2357	}
2358
2359	public:
2360	static constexpr unsigned fractional_width = {_S_fractional_width()};
2361
2362	using precision
2363	= duration<common_type_t<typename _Duration::rep,
2364	chrono::seconds::rep>,
2365	ratio<1, __detail::__pow10(fractional_width)>>;
2366
2367	constexpr hh_mm_ss() noexcept = default;
2368
2369	constexpr explicit
2370	hh_mm_ss(_Duration __d)
2371	: hh_mm_ss(_S_abs(__d), __d < _Duration::zero())
2372	{ }
2373
2374	constexpr bool
2375	is_negative() const noexcept
2376	{
2377	if constexpr (!_S_is_unsigned)
2378	return _M_is_neg;
2379	else
2380	return false;
2381	}
2382
2383	constexpr chrono::hours
2384	hours() const noexcept
2385	{ return _M_h; }
2386
2387	constexpr chrono::minutes
2388	minutes() const noexcept
2389	{ return _M_m; }
2390
2391	constexpr chrono::seconds
2392	seconds() const noexcept
2393	{ return _M_s; }
2394
2395	constexpr precision
2396	subseconds() const noexcept
2397	{ return static_cast<precision>(_M_ss); }
2398
2399	constexpr explicit
2400	operator precision() const noexcept
2401	{ return to_duration(); }
2402
2403	constexpr precision
2404	to_duration() const noexcept
2405	{
2406	if constexpr (!_S_is_unsigned)
2407	if (_M_is_neg)
2408	return -(_M_h + _M_m + _M_s + subseconds());
2409	return _M_h + _M_m + _M_s + subseconds();
2410	}
2411
2412	private:
2413	static constexpr bool _S_is_unsigned
2414	= __and_v<is_integral<typename _Duration::rep>,
2415	is_unsigned<typename _Duration::rep>>;
2416
2417	template<typename _Ratio>
2418	using __byte_duration = duration<unsigned char, _Ratio>;
2419
2420	// The type of the _M_ss member that holds the subsecond precision.
2421	template<typename _Dur>
2422	struct __subseconds
2423	{
2424	typename _Dur::rep _M_r{};
2425
2426	constexpr explicit
2427	operator _Dur() const noexcept
2428	{ return _Dur(_M_r); }
2429	};
2430
2431	// An empty class if this precision doesn't need subseconds.
2432	template<typename _Rep>
2433	requires (!treat_as_floating_point_v<_Rep>)
2434	struct __subseconds<duration<_Rep, ratio<1>>>
2435	{
2436	constexpr explicit
2437	operator duration<_Rep, ratio<1>>() const noexcept
2438	{ return {}; }
2439	};
2440
2441	// True if the maximum constructor argument can be represented in _Tp.
2442	template<typename _Tp>
2443	static constexpr bool __fits
2444	= duration_values<typename _Duration::rep>::max()
2445	<= duration_values<_Tp>::max();
2446
2447	template<typename _Rep, typename _Period>
2448	requires (!treat_as_floating_point_v<_Rep>)
2449	&& ratio_less_v<_Period, ratio<1, 1>>
2450	&& (ratio_greater_equal_v<_Period, ratio<1, 250>>
2451	|| __fits<unsigned char>)
2452	struct __subseconds<duration<_Rep, _Period>>
2453	{
2454	unsigned char _M_r{};
2455
2456	constexpr explicit
2457	operator duration<_Rep, _Period>() const noexcept
2458	{ return duration<_Rep, _Period>(_M_r); }
2459	};
2460
2461	template<typename _Rep, typename _Period>
2462	requires (!treat_as_floating_point_v<_Rep>)
2463	&& ratio_less_v<_Period, ratio<1, 250>>
2464	&& (ratio_greater_equal_v<_Period, ratio<1, 4000000000>>
2465	|| __fits<uint_least32_t>)
2466	struct __subseconds<duration<_Rep, _Period>>
2467	{
2468	uint_least32_t _M_r{};
2469
2470	constexpr explicit
2471	operator duration<_Rep, _Period>() const noexcept
2472	{ return duration<_Rep, _Period>(_M_r); }
2473	};
2474
2475	chrono::hours _M_h{};
2476	__byte_duration<ratio<60>> _M_m{};
2477	__byte_duration<ratio<1>> _M_s{};
2478	bool _M_is_neg{};
2479	__subseconds<precision> _M_ss{};
2480
2481	template<typename> friend struct __detail::__utc_leap_second;
2482	};
2483
2484	/// @cond undocumented
2485	namespace __detail
2486	{
2487	// Represents a time that is within a leap second insertion.
2488	template<typename _Duration>
2489	struct __utc_leap_second
2490	{
2491	explicit
2492	__utc_leap_second(const sys_time<_Duration>& __s)
2493	: _M_date(chrono::floor<days>(__s)), _M_time(__s - _M_date)
2494	{
2495	++_M_time._M_s;
2496	}
2497
2498	sys_days _M_date;
2499	hh_mm_ss<common_type_t<_Duration, days>> _M_time;
2500	};
2501	}
2502	/// @endcond
2503
2504	// 12/24 HOURS FUNCTIONS
2505
2506	constexpr bool
2507	is_am(const hours& __h) noexcept
2508	{ return 0h <= __h && __h <= 11h; }
2509
2510	constexpr bool
2511	is_pm(const hours& __h) noexcept
2512	{ return 12h <= __h && __h <= 23h; }
2513
2514	constexpr hours
2515	make12(const hours& __h) noexcept
2516	{
2517	if (__h == 0h)
2518	return 12h;
2519	else if (__h > 12h)
2520	return __h - 12h;
2521	return __h;
2522	}
2523
2524	constexpr hours
2525	make24(const hours& __h, bool __is_pm) noexcept
2526	{
2527	if (!__is_pm)
2528	{
2529	if (__h == 12h)
2530	return 0h;
2531	else
2532	return __h;
2533	}
2534	else
2535	{
2536	if (__h == 12h)
2537	return __h;
2538	else
2539	return __h + 12h;
2540	}
2541	}
2542
2543	#if _GLIBCXX_USE_CXX11_ABI || ! _GLIBCXX_USE_DUAL_ABI
2544	// C++20 [time.zones] Time zones
2545
2546	struct tzdb;
2547
2548	struct sys_info
2549	{
2550	sys_seconds begin;
2551	sys_seconds end;
2552	seconds offset;
2553	minutes save;
2554	string abbrev;
2555	};
2556
2557	struct local_info
2558	{
2559	static constexpr int unique = 0;
2560	static constexpr int nonexistent = 1;
2561	static constexpr int ambiguous = 2;
2562
2563	int result;
2564	sys_info first;
2565	sys_info second;
2566	};
2567
2568	class nonexistent_local_time : public runtime_error
2569	{
2570	public:
2571	template<typename _Duration>
2572	nonexistent_local_time(const local_time<_Duration>& __tp,
2573	const local_info& __i)
2574	: runtime_error(_S_make_what_str(__tp, __i))
2575	{ __glibcxx_assert(__i.result == local_info::nonexistent); }
2576
2577	private:
2578	template<typename _Duration>
2579	static string
2580	_S_make_what_str(const local_time<_Duration>& __tp,
2581	const local_info& __i)
2582	{
2583	std::ostringstream __os;
2584	__os << __tp << " is in a gap between\n"
2585	<< local_seconds(__i.first.end.time_since_epoch())
2586	+ __i.first.offset << ' ' << __i.first.abbrev << " and\n"
2587	<< local_seconds(__i.second.begin.time_since_epoch())
2588	+ __i.second.offset << ' ' << __i.second.abbrev
2589	<< " which are both equivalent to\n"
2590	<< __i.first.end << " UTC";
2591	return std::move(__os).str();
2592	}
2593	};
2594
2595	class ambiguous_local_time : public runtime_error
2596	{
2597	public:
2598	template<typename _Duration>
2599	ambiguous_local_time(const local_time<_Duration>& __tp,
2600	const local_info& __i)
2601	: runtime_error(_S_make_what_str(__tp, __i))
2602	{ __glibcxx_assert(__i.result == local_info::ambiguous); }
2603
2604	private:
2605	template<typename _Duration>
2606	static string
2607	_S_make_what_str(const local_time<_Duration>& __tp,
2608	const local_info& __i)
2609	{
2610	std::ostringstream __os;
2611	__os << __tp << " is ambiguous. It could be\n"
2612	<< __tp << ' ' << __i.first.abbrev << " == "
2613	<< __tp - __i.first.offset << " UTC or\n"
2614	<< __tp << ' ' << __i.second.abbrev << " == "
2615	<< __tp - __i.second.offset << " UTC";
2616	return std::move(__os).str();
2617	}
2618	};
2619
2620	template<typename _Duration>
2621	[[noreturn]] void
2622	__throw_bad_local_time(const local_time<_Duration>& __tp,
2623	const local_info& __i)
2624	{
2625	#if __cpp_exceptions
2626	if (__i.result == local_info::nonexistent)
2627	throw nonexistent_local_time(__tp, __i);
2628	throw ambiguous_local_time(__tp, __i);
2629	#else
2630	__builtin_abort();
2631	#endif
2632	}
2633
2634	enum class choose { earliest, latest };
2635
2636	class time_zone
2637	{
2638	public:
2639	time_zone(time_zone&&) = default;
2640	time_zone& operator=(time_zone&&) = default;
2641
2642	~time_zone();
2643
2644	[[nodiscard]]
2645	string_view name() const noexcept { return _M_name; }
2646
2647	template<typename _Duration>
2648	sys_info
2649	get_info(const sys_time<_Duration>& __st) const
2650	{ return _M_get_sys_info(chrono::floor<seconds>(__st)); }
2651
2652	template<typename _Duration>
2653	local_info
2654	get_info(const local_time<_Duration>& __tp) const
2655	{ return _M_get_local_info(chrono::floor<seconds>(__tp)); }
2656
2657	template<typename _Duration>
2658	sys_time<common_type_t<_Duration, seconds>>
2659	to_sys(const local_time<_Duration>& __tp) const
2660	{
2661	local_info __info = get_info(__tp);
2662
2663	if (__info.result != local_info::unique)
2664	__throw_bad_local_time(__tp, __info);
2665
2666	return sys_time<_Duration>(__tp.time_since_epoch())
2667	- __info.first.offset;
2668	}
2669
2670	template<typename _Duration>
2671	sys_time<common_type_t<_Duration, seconds>>
2672	to_sys(const local_time<_Duration>& __tp, choose __z) const
2673	{
2674	local_info __info = get_info(__tp);
2675
2676	if (__info.result == local_info::nonexistent)
2677	return __info.first.end; // Last second of the previous sys_info.
2678
2679	sys_time<_Duration> __st(__tp.time_since_epoch());
2680
2681	if (__info.result == local_info::ambiguous && __z == choose::latest)
2682	return __st - __info.second.offset; // Time in the later sys_info.
2683	// else if __z == earliest, use __info.first.offset as below:
2684
2685	return __st - __info.first.offset;
2686	}
2687
2688	template<typename _Duration>
2689	local_time<common_type_t<_Duration, seconds>>
2690	to_local(const sys_time<_Duration>& __tp) const
2691	{
2692	auto __d = (__tp + get_info(__tp).offset).time_since_epoch();
2693	return local_time<common_type_t<_Duration, seconds>>(__d);
2694	}
2695
2696	[[nodiscard]] friend bool
2697	operator==(const time_zone& __x, const time_zone& __y) noexcept
2698	{ return __x._M_name == __y._M_name; }
2699
2700	[[nodiscard]] friend strong_ordering
2701	operator<=>(const time_zone& __x, const time_zone& __y) noexcept
2702	{ return __x._M_name <=> __y._M_name; }
2703
2704	private:
2705	sys_info _M_get_sys_info(sys_seconds) const;
2706	local_info _M_get_local_info(local_seconds) const;
2707
2708	friend const tzdb& reload_tzdb();
2709	friend struct tzdb;
2710	friend class tzdb_list;
2711
2712	struct _Impl;
2713
2714	explicit time_zone(unique_ptr<_Impl> __p);
2715	string _M_name;
2716	unique_ptr<_Impl> _M_impl;
2717	};
2718
2719	const time_zone* locate_zone(string_view __tz_name);
2720	const time_zone* current_zone();
2721
2722	/** The list of `chrono::tzdb` objects
2723	*
2724	* A single object of this type is constructed by the C++ runtime,
2725	* and can be accessed by calling `chrono::get_tzdb_list()`.
2726	*
2727	* The front of the list is the current `tzdb` object and can be accessed
2728	* via `chrono::get_tzdb_list().front()` or `chrono::get_tzdb()` or
2729	* `*chrono::get_tzdb_list().begin()`.
2730	*
2731	* The `chrono::reload_tzdb()` function will check for a newer version
2732	* and if found, insert it at the front of the list.
2733	*
2734	* @since C++20
2735	*/
2736	class tzdb_list
2737	{
2738	struct _Node;
2739
2740	public:
2741	tzdb_list(const tzdb_list&) = delete;
2742	tzdb_list& operator=(const tzdb_list&) = delete;
2743
2744	/** An iterator into the `tzdb_list`
2745	*
2746	* As a extension, in libstdc++ each `tzdb` is reference-counted
2747	* and the `const_iterator` type shares ownership of the object it
2748	* refers to. This ensures that a `tzdb` erased from the list will
2749	* not be destroyed while there is an iterator that refers to it.
2750	*/
2751	class const_iterator
2752	{
2753	public:
2754	using value_type = tzdb;
2755	using reference = const tzdb&;
2756	using pointer = const tzdb*;
2757	using difference_type = ptrdiff_t;
2758	using iterator_category = forward_iterator_tag;
2759
2760	constexpr const_iterator() = default;
2761	const_iterator(const const_iterator&) = default;
2762	const_iterator(const_iterator&&) = default;
2763	const_iterator& operator=(const const_iterator&) = default;
2764	const_iterator& operator=(const_iterator&&) = default;
2765
2766	reference operator*() const noexcept;
2767	pointer operator->() const noexcept { return &**this; }
2768	const_iterator& operator++();
2769	const_iterator operator++(int);
2770
2771	bool operator==(const const_iterator&) const noexcept = default;
2772
2773	private:
2774	explicit const_iterator(const shared_ptr<_Node>&) noexcept;
2775
2776	friend class tzdb_list;
2777
2778	shared_ptr<_Node> _M_node;
2779	void* _M_reserved = nullptr;
2780	};
2781
2782	/** Access the current `tzdb` at the front of the list.
2783	*
2784	* This returns a reference to the same object as `chrono::get_tzdb()`.
2785	*
2786	* @returns A reference to the current tzdb object.
2787	* @since C++20
2788	*/
2789	const tzdb& front() const noexcept;
2790
2791	/** Remove the tzdb object _after_ the one the iterator refers to.
2792	*
2793	* Calling this function concurrently with any of `front()`, `begin()`,
2794	* or `end()` does not cause a data race, but in general this function
2795	* is not thread-safe. The behaviour may be undefined if erasing an
2796	* element from the list while another thread is calling the same
2797	* function, or incrementing an iterator into the list, or accessing
2798	* the element being erased (unless it is accessed through an iterator).
2799	*
2800	* @param __p A dereferenceable iterator.
2801	* @returns An iterator the element after the one that was erased
2802	* (or `end()` if there is no such element).
2803	* @since C++20
2804	*/
2805	const_iterator erase_after(const_iterator __p);
2806
2807	const_iterator begin() const noexcept;
2808	const_iterator end() const noexcept { return {}; }
2809	const_iterator cbegin() const noexcept { return begin(); }
2810	const_iterator cend() const noexcept { return end(); }
2811
2812	private:
2813	constexpr explicit tzdb_list(nullptr_t);
2814
2815	friend tzdb_list& get_tzdb_list();
2816	friend const tzdb& get_tzdb();
2817	friend const tzdb& reload_tzdb();
2818	friend struct tzdb;
2819	friend class leap_second;
2820	friend struct time_zone::_Impl;
2821	friend class time_zone_link;
2822	};
2823
2824	class time_zone_link
2825	{
2826	public:
2827	time_zone_link(time_zone_link&&) = default;
2828	time_zone_link& operator=(time_zone_link&&) = default;
2829
2830	string_view name() const noexcept { return _M_name; }
2831	string_view target() const noexcept { return _M_target; }
2832
2833	friend bool
2834	operator==(const time_zone_link& __x, const time_zone_link& __y) noexcept
2835	{ return __x.name() == __y.name(); }
2836
2837	friend strong_ordering
2838	operator<=>(const time_zone_link& __x, const time_zone_link& __y) noexcept
2839	{ return __x.name() <=> __y.name(); }
2840
2841	private:
2842	friend const tzdb& reload_tzdb();
2843	friend struct tzdb_list::_Node;
2844
2845	explicit time_zone_link(nullptr_t) { }
2846
2847	string _M_name;
2848	string _M_target;
2849	};
2850
2851	class leap_second
2852	{
2853	public:
2854	leap_second(const leap_second&) = default;
2855	leap_second& operator=(const leap_second&) = default;
2856
2857	[[nodiscard]]
2858	constexpr sys_seconds
2859	date() const noexcept
2860	{
2861	if (_M_s >= _M_s.zero()) [[likely]]
2862	return sys_seconds(_M_s);
2863	return sys_seconds(-_M_s);
2864	}
2865
2866	[[nodiscard]]
2867	constexpr seconds
2868	value() const noexcept
2869	{
2870	if (_M_s >= _M_s.zero()) [[likely]]
2871	return seconds(1);
2872	return seconds(-1);
2873	}
2874
2875	// This can be defaulted because the database will never contain two
2876	// leap_second objects with the same date but different signs.
2877	[[nodiscard]] friend constexpr bool
2878	operator==(const leap_second&, const leap_second&) noexcept = default;
2879
2880	[[nodiscard]] friend constexpr strong_ordering
2881	operator<=>(const leap_second& __x, const leap_second& __y) noexcept
2882	{ return __x.date() <=> __y.date(); }
2883
2884	template<typename _Duration>
2885	[[nodiscard]] friend constexpr bool
2886	operator==(const leap_second& __x,
2887	const sys_time<_Duration>& __y) noexcept
2888	{ return __x.date() == __y; }
2889
2890	template<typename _Duration>
2891	[[nodiscard]] friend constexpr bool
2892	operator<(const leap_second& __x,
2893	const sys_time<_Duration>& __y) noexcept
2894	{ return __x.date() < __y; }
2895
2896	template<typename _Duration>
2897	[[nodiscard]] friend constexpr bool
2898	operator<(const sys_time<_Duration>& __x,
2899	const leap_second& __y) noexcept
2900	{ return __x < __y.date(); }
2901
2902	template<typename _Duration>
2903	[[nodiscard]] friend constexpr bool
2904	operator>(const leap_second& __x,
2905	const sys_time<_Duration>& __y) noexcept
2906	{ return __y < __x.date(); }
2907
2908	template<typename _Duration>
2909	[[nodiscard]] friend constexpr bool
2910	operator>(const sys_time<_Duration>& __x,
2911	const leap_second& __y) noexcept
2912	{ return __y.date() < __x; }
2913
2914	template<typename _Duration>
2915	[[nodiscard]] friend constexpr bool
2916	operator<=(const leap_second& __x,
2917	const sys_time<_Duration>& __y) noexcept
2918	{ return !(__y < __x.date()); }
2919
2920	template<typename _Duration>
2921	[[nodiscard]] friend constexpr bool
2922	operator<=(const sys_time<_Duration>& __x,
2923	const leap_second& __y) noexcept
2924	{ return !(__y.date() < __x); }
2925
2926	template<typename _Duration>
2927	[[nodiscard]] friend constexpr bool
2928	operator>=(const leap_second& __x,
2929	const sys_time<_Duration>& __y) noexcept
2930	{ return !(__x.date() < __y); }
2931
2932	template<typename _Duration>
2933	[[nodiscard]] friend constexpr bool
2934	operator>=(const sys_time<_Duration>& __x,
2935	const leap_second& __y) noexcept
2936	{ return !(__x < __y.date()); }
2937
2938	template<three_way_comparable_with<seconds> _Duration>
2939	[[nodiscard]] friend constexpr auto
2940	operator<=>(const leap_second& __x,
2941	const sys_time<_Duration>& __y) noexcept
2942	{ return __x.date() <=> __y; }
2943
2944	private:
2945	explicit leap_second(seconds::rep __s) : _M_s(__s) { }
2946
2947	friend struct tzdb_list::_Node;
2948
2949	friend const tzdb& reload_tzdb();
2950
2951	template<typename _Duration>
2952	friend leap_second_info
2953	get_leap_second_info(const utc_time<_Duration>&);
2954
2955	seconds _M_s; // == date().time_since_epoch() * value().count()
2956	};
2957
2958	template<class _Tp> struct zoned_traits { };
2959
2960	template<>
2961	struct zoned_traits<const time_zone*>
2962	{
2963	static const time_zone*
2964	default_zone()
2965	{ return std::chrono::locate_zone("UTC"); }
2966
2967	static const time_zone*
2968	locate_zone(string_view __name)
2969	{ return std::chrono::locate_zone(__name); }
2970	};
2971
2972	struct tzdb
2973	{
2974	string version;
2975	_GLIBCXX_STD_C::vector<time_zone> zones;
2976	_GLIBCXX_STD_C::vector<time_zone_link> links;
2977	_GLIBCXX_STD_C::vector<leap_second> leap_seconds;
2978
2979	const time_zone*
2980	locate_zone(string_view __tz_name) const;
2981
2982	const time_zone*
2983	current_zone() const;
2984
2985	private:
2986	friend const tzdb& reload_tzdb();
2987	friend class time_zone;
2988	friend struct tzdb_list::_Node;
2989	};
2990
2991	tzdb_list& get_tzdb_list();
2992	const tzdb& get_tzdb();
2993
2994	const tzdb& reload_tzdb();
2995	string remote_version();
2996
2997	template<typename _Duration, typename _TimeZonePtr = const time_zone*>
2998	class zoned_time
2999	{
3000	static_assert(__is_duration_v<_Duration>);
3001
3002	using _Traits = zoned_traits<_TimeZonePtr>;
3003
3004	// Every constructor that accepts a string_view as its first parameter
3005	// does not participate in class template argument deduction.
3006	using string_view = type_identity_t<std::string_view>;
3007
3008	public:
3009	using duration = common_type_t<_Duration, seconds>;
3010
3011	zoned_time() requires requires { _Traits::default_zone(); }
3012	{ }
3013
3014	zoned_time(const zoned_time&) = default;
3015	zoned_time& operator=(const zoned_time&) = default;
3016
3017	zoned_time(const sys_time<_Duration>& __st)
3018	requires requires { _Traits::default_zone(); }
3019	: _M_tp(__st)
3020	{ }
3021
3022	explicit
3023	zoned_time(_TimeZonePtr __z) : _M_zone(std::move(__z)) { }
3024
3025	explicit
3026	zoned_time(string_view __name)
3027	requires requires {
3028	_TimeZonePtr{_Traits::locate_zone(std::string_view{})};
3029	}
3030	: _M_zone(_Traits::locate_zone(__name))
3031	{ }
3032
3033	template<typename _Duration2>
3034	zoned_time(const zoned_time<_Duration2, _TimeZonePtr>& __zt)
3035	requires is_convertible_v<sys_time<_Duration2>, sys_time<_Duration>>
3036	: _M_zone(__zt._M_zone), _M_tp(__zt._M_tp)
3037	{ }
3038
3039	zoned_time(_TimeZonePtr __z, const sys_time<_Duration>& __st)
3040	: _M_zone(std::move(__z)), _M_tp(__st)
3041	{ }
3042
3043	zoned_time(string_view __name, const sys_time<_Duration>& __st)
3044	: zoned_time(_Traits::locate_zone(__name), __st)
3045	{ }
3046
3047	zoned_time(_TimeZonePtr __z, const local_time<_Duration>& __tp)
3048	requires requires {
3049	{ __z->to_sys(__tp) } -> convertible_to<sys_time<_Duration>>;
3050	}
3051	: _M_zone(std::move(__z)), _M_tp(_M_zone->to_sys(__tp))
3052	{ }
3053
3054	zoned_time(string_view __name, const local_time<_Duration>& __tp)
3055	requires requires (_TimeZonePtr __z) {
3056	{ _Traits::locate_zone(__name) } -> convertible_to<_TimeZonePtr>;
3057	{ __z->to_sys(__tp) } -> convertible_to<sys_time<_Duration>>;
3058	}
3059	: zoned_time(_Traits::locate_zone(__name), __tp)
3060	{ }
3061
3062	zoned_time(_TimeZonePtr __z, const local_time<_Duration>& __tp,
3063	choose __c)
3064	requires requires {
3065	{ __z->to_sys(__tp, __c) } -> convertible_to<sys_time<_Duration>>;
3066	}
3067	: _M_zone(std::move(__z)), _M_tp(_M_zone->to_sys(__tp, __c))
3068	{ }
3069
3070	zoned_time(string_view __name, const local_time<_Duration>& __tp,
3071	choose __c)
3072	requires requires (_TimeZonePtr __z) {
3073	{ _Traits::locate_zone(__name) } -> convertible_to<_TimeZonePtr>;
3074	{ __z->to_sys(__tp, __c) } -> convertible_to<sys_time<_Duration>>;
3075	}
3076	: _M_zone(_Traits::locate_zone(__name)),
3077	_M_tp(_M_zone->to_sys(__tp, __c))
3078	{ }
3079
3080	template<typename _Duration2, typename _TimeZonePtr2>
3081	zoned_time(_TimeZonePtr __z,
3082	const zoned_time<_Duration2, _TimeZonePtr2>& __zt)
3083	requires is_convertible_v<sys_time<_Duration2>, sys_time<_Duration>>
3084	: _M_zone(__z), _M_tp(__zt._M_tp)
3085	{ }
3086
3087	template<typename _Duration2, typename _TimeZonePtr2>
3088	zoned_time(_TimeZonePtr __z,
3089	const zoned_time<_Duration2, _TimeZonePtr2>& __zt,
3090	choose)
3091	requires is_convertible_v<sys_time<_Duration2>, sys_time<_Duration>>
3092	: _M_zone(__z), _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	requires is_convertible_v<sys_time<_Duration2>, sys_time<_Duration>>
3099	&& requires {
3100	{ _Traits::locate_zone(__name) } -> convertible_to<_TimeZonePtr>;
3101	}
3102	: _M_zone(_Traits::locate_zone(__name)), _M_tp(__zt._M_tp)
3103	{ }
3104
3105	template<typename _Duration2, typename _TimeZonePtr2>
3106	zoned_time(string_view __name,
3107	const zoned_time<_Duration2, _TimeZonePtr2>& __zt,
3108	choose)
3109	requires is_convertible_v<sys_time<_Duration2>, sys_time<_Duration>>
3110	&& requires {
3111	{ _Traits::locate_zone(__name) } -> convertible_to<_TimeZonePtr>;
3112	}
3113	: _M_zone(_Traits::locate_zone(__name)), _M_tp(__zt._M_tp)
3114	{ }
3115
3116	zoned_time&
3117	operator=(const sys_time<_Duration>& __st)
3118	{
3119	_M_tp = __st;
3120	return *this;
3121	}
3122
3123	zoned_time&
3124	operator=(const local_time<_Duration>& __lt)
3125	{
3126	_M_tp = _M_zone->to_sys(__lt);
3127	return *this;
3128	}
3129
3130	[[nodiscard]]
3131	operator sys_time<duration>() const { return _M_tp; }
3132
3133	[[nodiscard]]
3134	explicit operator local_time<duration>() const
3135	{ return get_local_time(); }
3136
3137	[[nodiscard]]
3138	_TimeZonePtr
3139	get_time_zone() const
3140	{ return _M_zone; }
3141
3142	[[nodiscard]]
3143	local_time<duration>
3144	get_local_time() const
3145	{ return _M_zone->to_local(_M_tp); }
3146
3147	[[nodiscard]]
3148	sys_time<duration>
3149	get_sys_time() const
3150	{ return _M_tp; }
3151
3152	[[nodiscard]]
3153	sys_info
3154	get_info() const
3155	{ return _M_zone->get_info(_M_tp); }
3156
3157	[[nodiscard]] friend bool
3158	operator==(const zoned_time&, const zoned_time&) = default;
3159
3160	private:
3161	_TimeZonePtr _M_zone{ _Traits::default_zone() };
3162	sys_time<duration> _M_tp{};
3163
3164	template<typename _Duration2, typename _TimeZonePtr2>
3165	friend class zoned_time;
3166	};
3167
3168	zoned_time() -> zoned_time<seconds>;
3169
3170	template<typename _Duration>
3171	zoned_time(sys_time<_Duration>)
3172	-> zoned_time<common_type_t<_Duration, seconds>>;
3173
3174	/// @cond undocumented
3175	template<typename _TimeZonePtrOrName>
3176	using __time_zone_representation
3177	= __conditional_t<is_convertible_v<_TimeZonePtrOrName, string_view>,
3178	const time_zone*,
3179	remove_cvref_t<_TimeZonePtrOrName>>;
3180	/// @endcond
3181
3182	template<typename _TimeZonePtrOrName>
3183	zoned_time(_TimeZonePtrOrName&&)
3184	-> zoned_time<seconds, __time_zone_representation<_TimeZonePtrOrName>>;
3185
3186	template<typename _TimeZonePtrOrName, typename _Duration>
3187	zoned_time(_TimeZonePtrOrName&&, sys_time<_Duration>)
3188	-> zoned_time<common_type_t<_Duration, seconds>,
3189	__time_zone_representation<_TimeZonePtrOrName>>;
3190
3191	template<typename _TimeZonePtrOrName, typename _Duration>
3192	zoned_time(_TimeZonePtrOrName&&, local_time<_Duration>,
3193	choose = choose::earliest)
3194	-> zoned_time<common_type_t<_Duration, seconds>,
3195	__time_zone_representation<_TimeZonePtrOrName>>;
3196
3197	template<typename _Duration, typename _TimeZonePtrOrName,
3198	typename _TimeZonePtr2>
3199	zoned_time(_TimeZonePtrOrName&&, zoned_time<_Duration, _TimeZonePtr2>,
3200	choose = choose::earliest)
3201	-> zoned_time<common_type_t<_Duration, seconds>,
3202	__time_zone_representation<_TimeZonePtrOrName>>;
3203
3204	template<typename _Dur1, typename _TZPtr1, typename _Dur2, typename _TZPtr2>
3205	[[nodiscard]]
3206	inline bool
3207	operator==(const zoned_time<_Dur1, _TZPtr1>& __x,
3208	const zoned_time<_Dur2, _TZPtr2>& __y)
3209	{
3210	return __x.get_time_zone() == __y.get_time_zone()
3211	&& __x.get_sys_time() == __y.get_sys_time();
3212	}
3213
3214	using zoned_seconds = zoned_time<seconds>;
3215	#endif // _GLIBCXX_USE_CXX11_ABI || ! _GLIBCXX_USE_DUAL_ABI
3216
3217	namespace __detail
3218	{
3219	inline leap_second_info
3220	__get_leap_second_info(sys_seconds __ss, bool __is_utc)
3221	{
3222	if (__ss < sys_seconds{}) [[unlikely]]
3223	return {};
3224
3225	const seconds::rep __leaps[] {
3226	78796800, // 1 Jul 1972
3227	94694400, // 1 Jan 1973
3228	126230400, // 1 Jan 1974
3229	157766400, // 1 Jan 1975
3230	189302400, // 1 Jan 1976
3231	220924800, // 1 Jan 1977
3232	252460800, // 1 Jan 1978
3233	283996800, // 1 Jan 1979
3234	315532800, // 1 Jan 1980
3235	362793600, // 1 Jul 1981
3236	394329600, // 1 Jul 1982
3237	425865600, // 1 Jul 1983
3238	489024000, // 1 Jul 1985
3239	567993600, // 1 Jan 1988
3240	631152000, // 1 Jan 1990
3241	662688000, // 1 Jan 1991
3242	709948800, // 1 Jul 1992
3243	741484800, // 1 Jul 1993
3244	773020800, // 1 Jul 1994
3245	820454400, // 1 Jan 1996
3246	867715200, // 1 Jul 1997
3247	915148800, // 1 Jan 1999
3248	1136073600, // 1 Jan 2006
3249	1230768000, // 1 Jan 2009
3250	1341100800, // 1 Jul 2012
3251	1435708800, // 1 Jul 2015
3252	1483228800, // 1 Jan 2017
3253	};
3254	// The list above is known to be valid until (at least) this date
3255	// and only contains positive leap seconds.
3256	const sys_seconds __expires(1735344000s); // 2024-12-28 00:00:00 UTC
3257
3258	#if _GLIBCXX_USE_CXX11_ABI || ! _GLIBCXX_USE_DUAL_ABI
3259	if (__ss > __expires)
3260	{
3261	// Use updated leap_seconds from tzdb.
3262	size_t __n = std::size(__leaps);
3263
3264	auto __db = get_tzdb_list().begin();
3265	auto __first = __db->leap_seconds.begin() + __n;
3266	auto __last = __db->leap_seconds.end();
3267	auto __pos = std::upper_bound(__first, __last, __ss);
3268	seconds __elapsed(__n);
3269	for (auto __i = __first; __i != __pos; ++__i)
3270	__elapsed += __i->value();
3271
3272	if (__is_utc)
3273	{
3274	// Convert utc_time to sys_time:
3275	__ss -= __elapsed;
3276	// See if that sys_time is before (or during) previous leap sec:
3277	if (__pos != __first && __ss < __pos[-1])
3278	{
3279	if ((__ss + 1s) >= __pos[-1])
3280	return {true, __elapsed};
3281	__elapsed -= __pos[-1].value();
3282	}
3283	}
3284	return {false, __elapsed};
3285	}
3286	else
3287	#endif
3288	{
3289	seconds::rep __s = __ss.time_since_epoch().count();
3290	const seconds::rep* __first = std::begin(__leaps);
3291	const seconds::rep* __last = std::end(__leaps);
3292
3293	// Don't bother searching the list if we're after the last one.
3294	if (__s > (__last[-1] + (__last - __first) + 1))
3295	return { false, seconds(__last - __first) };
3296
3297	auto __pos = std::upper_bound(__first, __last, __s);
3298	seconds __elapsed{__pos - __first};
3299	if (__is_utc)
3300	{
3301	// Convert utc_time to sys_time:
3302	__s -= __elapsed.count();
3303	// See if that sys_time is before (or during) previous leap sec:
3304	if (__pos != __first && __s < __pos[-1])
3305	{
3306	if ((__s + 1) >= __pos[-1])
3307	return {true, __elapsed};
3308	--__elapsed;
3309	}
3310	}
3311	return {false, __elapsed};
3312	}
3313	}
3314	} // namespace __detail
3315
3316	template<typename _Duration>
3317	[[nodiscard]]
3318	inline leap_second_info
3319	get_leap_second_info(const utc_time<_Duration>& __ut)
3320	{
3321	auto __s = chrono::duration_cast<seconds>(__ut.time_since_epoch());
3322	return __detail::__get_leap_second_info(sys_seconds(__s), true);
3323	}
3324
3325	template<typename _Duration>
3326	[[nodiscard]]
3327	inline utc_time<common_type_t<_Duration, seconds>>
3328	utc_clock::from_sys(const sys_time<_Duration>& __t)
3329	{
3330	using _CDur = common_type_t<_Duration, seconds>;
3331	auto __s = chrono::time_point_cast<seconds>(__t);
3332	const auto __li = __detail::__get_leap_second_info(__s, false);
3333	return utc_time<_CDur>{__t.time_since_epoch()} + __li.elapsed;
3334	}
3335
3336	/// @} group chrono
3337	#endif // C++20
3338	} // namespace chrono
3339
3340	#if __cplusplus >= 202002L
3341	inline namespace literals
3342	{
3343	inline namespace chrono_literals
3344	{
3345	/// @addtogroup chrono
3346	/// @{
3347	#pragma GCC diagnostic push
3348	#pragma GCC diagnostic ignored "-Wliteral-suffix"
3349	/// Literal suffix for creating chrono::day objects.
3350	/// @since C++20
3351	constexpr chrono::day
3352	operator""d(unsigned long long __d) noexcept
3353	{ return chrono::day{static_cast<unsigned>(__d)}; }
3354
3355	/// Literal suffix for creating chrono::year objects.
3356	/// @since C++20
3357	constexpr chrono::year
3358	operator""y(unsigned long long __y) noexcept
3359	{ return chrono::year{static_cast<int>(__y)}; }
3360	#pragma GCC diagnostic pop
3361	/// @}
3362	} // inline namespace chrono_literals
3363	} // inline namespace literals
3364	#endif // C++20
3365
3366	_GLIBCXX_END_NAMESPACE_VERSION
3367	} // namespace std
3368
3369	#if __cplusplus >= 202002L
3370	# include <bits/chrono_io.h>
3371	#endif
3372
3373	#endif // C++11
3374
3375	#endif //_GLIBCXX_CHRONO
3376