1// <chrono> -*- C++ -*-
2
3// Copyright (C) 2008-2021 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#if __cplusplus < 201103L
36# include <bits/c++0x_warning.h>
37#else
38
39#include <ratio>
40#include <type_traits>
41#include <limits>
42#include <ctime>
43#include <bits/parse_numbers.h> // for literals support.
44#if __cplusplus > 201703L
45# include <concepts>
46# include <compare>
47#endif
48
49namespace std _GLIBCXX_VISIBILITY(default)
50{
51_GLIBCXX_BEGIN_NAMESPACE_VERSION
52
53#if __cplusplus >= 201703L
54  namespace filesystem { struct __file_clock; };
55#endif
56
57  /**
58   * @defgroup chrono Time
59   * @ingroup utilities
60   *
61   * Classes and functions for time.
62   *
63   * @since C++11
64   */
65
66  /** @namespace std::chrono
67   *  @brief ISO C++ 2011 namespace for date and time utilities
68   *  @ingroup chrono
69   */
70  namespace chrono
71  {
72    /// @addtogroup chrono
73    /// @{
74
75    /// `chrono::duration` represents a distance between two points in time
76    template<typename _Rep, typename _Period = ratio<1>>
77      struct duration;
78
79    /// `chrono::time_point` represents a point in time as measured by a clock
80    template<typename _Clock, typename _Dur = typename _Clock::duration>
81      struct time_point;
82    /// @}
83  }
84
85  /// @addtogroup chrono
86  /// @{
87
88  // 20.11.4.3 specialization of common_type (for duration, sfinae-friendly)
89
90  /// @cond undocumented
91
92  template<typename _CT, typename _Period1, typename _Period2, typename = void>
93    struct __duration_common_type
94    { };
95
96  template<typename _CT, typename _Period1, typename _Period2>
97    struct __duration_common_type<_CT, _Period1, _Period2,
98				  __void_t<typename _CT::type>>
99    {
100    private:
101      using __gcd_num = __static_gcd<_Period1::num, _Period2::num>;
102      using __gcd_den = __static_gcd<_Period1::den, _Period2::den>;
103      using __cr = typename _CT::type;
104      using __r = ratio<__gcd_num::value,
105			(_Period1::den / __gcd_den::value) * _Period2::den>;
106
107    public:
108      using type = chrono::duration<__cr, typename __r::type>;
109    };
110
111  /// @endcond
112
113  /// @{
114  /// @relates chrono::duration
115
116  /// Specialization of common_type for chrono::duration types.
117  template<typename _Rep1, typename _Period1, typename _Rep2, typename _Period2>
118    struct common_type<chrono::duration<_Rep1, _Period1>,
119		       chrono::duration<_Rep2, _Period2>>
120    : __duration_common_type<common_type<_Rep1, _Rep2>,
121			     typename _Period1::type,
122			     typename _Period2::type>
123    { };
124
125  /// Specialization of common_type for two identical chrono::duration types.
126  template<typename _Rep, typename _Period>
127    struct common_type<chrono::duration<_Rep, _Period>,
128		       chrono::duration<_Rep, _Period>>
129    {
130      using type = chrono::duration<typename common_type<_Rep>::type,
131				    typename _Period::type>;
132    };
133
134  /// Specialization of common_type for one chrono::duration type.
135  template<typename _Rep, typename _Period>
136    struct common_type<chrono::duration<_Rep, _Period>>
137    {
138      using type = chrono::duration<typename common_type<_Rep>::type,
139				    typename _Period::type>;
140    };
141  /// @}
142
143  // 20.11.4.3 specialization of common_type (for time_point, sfinae-friendly)
144
145  /// @cond undocumented
146
147  template<typename _CT, typename _Clock, typename = void>
148    struct __timepoint_common_type
149    { };
150
151  template<typename _CT, typename _Clock>
152    struct __timepoint_common_type<_CT, _Clock, __void_t<typename _CT::type>>
153    {
154      using type = chrono::time_point<_Clock, typename _CT::type>;
155    };
156
157  /// @endcond
158
159  /// @{
160  /// @relates chrono::time_point
161
162  /// Specialization of common_type for chrono::time_point types.
163  template<typename _Clock, typename _Duration1, typename _Duration2>
164    struct common_type<chrono::time_point<_Clock, _Duration1>,
165		       chrono::time_point<_Clock, _Duration2>>
166    : __timepoint_common_type<common_type<_Duration1, _Duration2>, _Clock>
167    { };
168
169  /// Specialization of common_type for two identical chrono::time_point types.
170  template<typename _Clock, typename _Duration>
171    struct common_type<chrono::time_point<_Clock, _Duration>,
172		       chrono::time_point<_Clock, _Duration>>
173    { using type = chrono::time_point<_Clock, _Duration>; };
174
175  /// Specialization of common_type for one chrono::time_point type.
176  template<typename _Clock, typename _Duration>
177    struct common_type<chrono::time_point<_Clock, _Duration>>
178    { using type = chrono::time_point<_Clock, _Duration>; };
179  /// @}
180
181  /// @} group chrono
182
183  namespace chrono
184  {
185    /// @addtogroup chrono
186    /// @{
187
188    /// @cond undocumented
189
190    // Primary template for duration_cast impl.
191    template<typename _ToDur, typename _CF, typename _CR,
192	     bool _NumIsOne = false, bool _DenIsOne = false>
193      struct __duration_cast_impl
194      {
195	template<typename _Rep, typename _Period>
196	  static constexpr _ToDur
197	  __cast(const duration<_Rep, _Period>& __d)
198	  {
199	    typedef typename _ToDur::rep			__to_rep;
200	    return _ToDur(static_cast<__to_rep>(static_cast<_CR>(__d.count())
201	      * static_cast<_CR>(_CF::num)
202	      / static_cast<_CR>(_CF::den)));
203	  }
204      };
205
206    template<typename _ToDur, typename _CF, typename _CR>
207      struct __duration_cast_impl<_ToDur, _CF, _CR, true, true>
208      {
209	template<typename _Rep, typename _Period>
210	  static constexpr _ToDur
211	  __cast(const duration<_Rep, _Period>& __d)
212	  {
213	    typedef typename _ToDur::rep			__to_rep;
214	    return _ToDur(static_cast<__to_rep>(__d.count()));
215	  }
216      };
217
218    template<typename _ToDur, typename _CF, typename _CR>
219      struct __duration_cast_impl<_ToDur, _CF, _CR, true, false>
220      {
221	template<typename _Rep, typename _Period>
222	  static constexpr _ToDur
223	  __cast(const duration<_Rep, _Period>& __d)
224	  {
225	    typedef typename _ToDur::rep			__to_rep;
226	    return _ToDur(static_cast<__to_rep>(
227	      static_cast<_CR>(__d.count()) / static_cast<_CR>(_CF::den)));
228	  }
229      };
230
231    template<typename _ToDur, typename _CF, typename _CR>
232      struct __duration_cast_impl<_ToDur, _CF, _CR, false, true>
233      {
234	template<typename _Rep, typename _Period>
235	  static constexpr _ToDur
236	  __cast(const duration<_Rep, _Period>& __d)
237	  {
238	    typedef typename _ToDur::rep			__to_rep;
239	    return _ToDur(static_cast<__to_rep>(
240	      static_cast<_CR>(__d.count()) * static_cast<_CR>(_CF::num)));
241	  }
242      };
243
244    template<typename _Tp>
245      struct __is_duration
246      : std::false_type
247      { };
248
249    template<typename _Rep, typename _Period>
250      struct __is_duration<duration<_Rep, _Period>>
251      : std::true_type
252      { };
253
254    template<typename _Tp>
255      using __enable_if_is_duration
256	= typename enable_if<__is_duration<_Tp>::value, _Tp>::type;
257
258    template<typename _Tp>
259      using __disable_if_is_duration
260	= typename enable_if<!__is_duration<_Tp>::value, _Tp>::type;
261
262    /// @endcond
263
264    /// duration_cast
265    template<typename _ToDur, typename _Rep, typename _Period>
266      constexpr __enable_if_is_duration<_ToDur>
267      duration_cast(const duration<_Rep, _Period>& __d)
268      {
269	typedef typename _ToDur::period				__to_period;
270	typedef typename _ToDur::rep				__to_rep;
271	typedef ratio_divide<_Period, __to_period> 		__cf;
272	typedef typename common_type<__to_rep, _Rep, intmax_t>::type
273	  							__cr;
274	typedef  __duration_cast_impl<_ToDur, __cf, __cr,
275				      __cf::num == 1, __cf::den == 1> __dc;
276	return __dc::__cast(__d);
277      }
278
279    /// treat_as_floating_point
280    template<typename _Rep>
281      struct treat_as_floating_point
282      : is_floating_point<_Rep>
283      { };
284
285#if __cplusplus > 201402L
286    template <typename _Rep>
287      inline constexpr bool treat_as_floating_point_v =
288        treat_as_floating_point<_Rep>::value;
289#endif // C++17
290
291#if __cplusplus > 201703L
292    template<typename _Tp>
293      struct is_clock;
294
295    template<typename _Tp>
296      inline constexpr bool is_clock_v = is_clock<_Tp>::value;
297
298#if __cpp_lib_concepts
299    template<typename _Tp>
300      struct is_clock : false_type
301      { };
302
303    template<typename _Tp>
304      requires requires {
305	typename _Tp::rep;
306	typename _Tp::period;
307	typename _Tp::duration;
308	typename _Tp::time_point::clock;
309	typename _Tp::time_point::duration;
310	{ &_Tp::is_steady } -> same_as<const bool*>;
311	{ _Tp::now() } -> same_as<typename _Tp::time_point>;
312	requires same_as<typename _Tp::duration,
313			 duration<typename _Tp::rep, typename _Tp::period>>;
314	requires same_as<typename _Tp::time_point::duration,
315			 typename _Tp::duration>;
316      }
317      struct is_clock<_Tp> : true_type
318      { };
319#else
320    template<typename _Tp, typename = void>
321      struct __is_clock_impl : false_type
322      { };
323
324    template<typename _Tp>
325      struct __is_clock_impl<_Tp,
326			     void_t<typename _Tp::rep, typename _Tp::period,
327				    typename _Tp::duration,
328				    typename _Tp::time_point::duration,
329				    decltype(_Tp::is_steady),
330				    decltype(_Tp::now())>>
331      : __and_<is_same<typename _Tp::duration,
332		       duration<typename _Tp::rep, typename _Tp::period>>,
333	       is_same<typename _Tp::time_point::duration,
334		       typename _Tp::duration>,
335	       is_same<decltype(&_Tp::is_steady), const bool*>,
336	       is_same<decltype(_Tp::now()), typename _Tp::time_point>>::type
337      { };
338
339    template<typename _Tp>
340      struct is_clock : __is_clock_impl<_Tp>::type
341      { };
342#endif
343#endif // C++20
344
345#if __cplusplus >= 201703L
346# define __cpp_lib_chrono 201611
347
348    template<typename _ToDur, typename _Rep, typename _Period>
349      constexpr __enable_if_is_duration<_ToDur>
350      floor(const duration<_Rep, _Period>& __d)
351      {
352	auto __to = chrono::duration_cast<_ToDur>(__d);
353	if (__to > __d)
354	  return __to - _ToDur{1};
355	return __to;
356      }
357
358    template<typename _ToDur, typename _Rep, typename _Period>
359      constexpr __enable_if_is_duration<_ToDur>
360      ceil(const duration<_Rep, _Period>& __d)
361      {
362	auto __to = chrono::duration_cast<_ToDur>(__d);
363	if (__to < __d)
364	  return __to + _ToDur{1};
365	return __to;
366      }
367
368    template <typename _ToDur, typename _Rep, typename _Period>
369      constexpr enable_if_t<
370	__and_<__is_duration<_ToDur>,
371	       __not_<treat_as_floating_point<typename _ToDur::rep>>>::value,
372	_ToDur>
373      round(const duration<_Rep, _Period>& __d)
374      {
375	_ToDur __t0 = chrono::floor<_ToDur>(__d);
376	_ToDur __t1 = __t0 + _ToDur{1};
377	auto __diff0 = __d - __t0;
378	auto __diff1 = __t1 - __d;
379	if (__diff0 == __diff1)
380	{
381	    if (__t0.count() & 1)
382		return __t1;
383	    return __t0;
384	}
385	else if (__diff0 < __diff1)
386	    return __t0;
387	return __t1;
388      }
389
390    template<typename _Rep, typename _Period>
391      constexpr
392      enable_if_t<numeric_limits<_Rep>::is_signed, duration<_Rep, _Period>>
393      abs(duration<_Rep, _Period> __d)
394      {
395	if (__d >= __d.zero())
396	  return __d;
397	return -__d;
398      }
399
400    // Make chrono::ceil<D> also usable as chrono::__detail::ceil<D>.
401    namespace __detail { using chrono::ceil; }
402
403#else // ! C++17
404
405    // We want to use ceil even when compiling for earlier standards versions.
406    // C++11 only allows a single statement in a constexpr function, so we
407    // need to move the comparison into a separate function, __ceil_impl.
408    namespace __detail
409    {
410      template<typename _Tp, typename _Up>
411	constexpr _Tp
412	__ceil_impl(const _Tp& __t, const _Up& __u)
413	{
414	  return (__t < __u) ? (__t + _Tp{1}) : __t;
415	}
416
417      // C++11-friendly version of std::chrono::ceil<D> for internal use.
418      template<typename _ToDur, typename _Rep, typename _Period>
419	constexpr _ToDur
420	ceil(const duration<_Rep, _Period>& __d)
421	{
422	  return __detail::__ceil_impl(chrono::duration_cast<_ToDur>(__d), __d);
423	}
424    }
425#endif // C++17
426
427    /// duration_values
428    template<typename _Rep>
429      struct duration_values
430      {
431	static constexpr _Rep
432	zero() noexcept
433	{ return _Rep(0); }
434
435	static constexpr _Rep
436	max() noexcept
437	{ return numeric_limits<_Rep>::max(); }
438
439	static constexpr _Rep
440	min() noexcept
441	{ return numeric_limits<_Rep>::lowest(); }
442      };
443
444    /// @cond undocumented
445
446    template<typename _Tp>
447      struct __is_ratio
448      : std::false_type
449      { };
450
451    template<intmax_t _Num, intmax_t _Den>
452      struct __is_ratio<ratio<_Num, _Den>>
453      : std::true_type
454      { };
455
456    /// @endcond
457
458    template<typename _Rep, typename _Period>
459      struct duration
460      {
461      private:
462	template<typename _Rep2>
463	  using __is_float = treat_as_floating_point<_Rep2>;
464
465	static constexpr intmax_t
466	_S_gcd(intmax_t __m, intmax_t __n) noexcept
467	{
468	  // Duration only allows positive periods so we don't need to
469	  // handle negative values here (unlike __static_gcd and std::gcd).
470#if __cplusplus >= 201402L
471	  do
472	    {
473	      intmax_t __rem = __m % __n;
474	      __m = __n;
475	      __n = __rem;
476	    }
477	  while (__n != 0);
478	  return __m;
479#else
480	  // C++11 doesn't allow loops in constexpr functions, but this
481	  // recursive version can be more expensive to evaluate.
482	  return (__n == 0) ? __m : _S_gcd(__n, __m % __n);
483#endif
484	}
485
486	// _GLIBCXX_RESOLVE_LIB_DEFECTS
487	// 2094. overflow shouldn't participate in overload resolution
488	// 3090. What is [2094] intended to mean?
489	// This only produces a valid type if no overflow occurs.
490	template<typename _R1, typename _R2,
491		 intmax_t __gcd1 = _S_gcd(_R1::num, _R2::num),
492		 intmax_t __gcd2 = _S_gcd(_R1::den, _R2::den)>
493	  using __divide = ratio<(_R1::num / __gcd1) * (_R2::den / __gcd2),
494				 (_R1::den / __gcd2) * (_R2::num / __gcd1)>;
495
496	// _Period2 is an exact multiple of _Period
497	template<typename _Period2>
498	  using __is_harmonic
499	    = __bool_constant<__divide<_Period2, _Period>::den == 1>;
500
501      public:
502
503	using rep = _Rep;
504	using period = typename _Period::type;
505
506	static_assert(!__is_duration<_Rep>::value, "rep cannot be a duration");
507	static_assert(__is_ratio<_Period>::value,
508		      "period must be a specialization of ratio");
509	static_assert(_Period::num > 0, "period must be positive");
510
511	// 20.11.5.1 construction / copy / destroy
512	constexpr duration() = default;
513
514	duration(const duration&) = default;
515
516	// _GLIBCXX_RESOLVE_LIB_DEFECTS
517	// 3050. Conversion specification problem in chrono::duration
518	template<typename _Rep2, typename = _Require<
519		 is_convertible<const _Rep2&, rep>,
520		 __or_<__is_float<rep>, __not_<__is_float<_Rep2>>>>>
521	  constexpr explicit duration(const _Rep2& __rep)
522	  : __r(static_cast<rep>(__rep)) { }
523
524	template<typename _Rep2, typename _Period2, typename = _Require<
525		 is_convertible<const _Rep2&, rep>,
526		 __or_<__is_float<rep>,
527		       __and_<__is_harmonic<_Period2>,
528			      __not_<__is_float<_Rep2>>>>>>
529	  constexpr duration(const duration<_Rep2, _Period2>& __d)
530	  : __r(duration_cast<duration>(__d).count()) { }
531
532	~duration() = default;
533	duration& operator=(const duration&) = default;
534
535	// 20.11.5.2 observer
536	constexpr rep
537	count() const
538	{ return __r; }
539
540	// 20.11.5.3 arithmetic
541
542	constexpr duration<typename common_type<rep>::type, period>
543	operator+() const
544	{ return duration<typename common_type<rep>::type, period>(__r); }
545
546	constexpr duration<typename common_type<rep>::type, period>
547	operator-() const
548	{ return duration<typename common_type<rep>::type, period>(-__r); }
549
550	_GLIBCXX17_CONSTEXPR duration&
551	operator++()
552	{
553	  ++__r;
554	  return *this;
555	}
556
557	_GLIBCXX17_CONSTEXPR duration
558	operator++(int)
559	{ return duration(__r++); }
560
561	_GLIBCXX17_CONSTEXPR duration&
562	operator--()
563	{
564	  --__r;
565	  return *this;
566	}
567
568	_GLIBCXX17_CONSTEXPR duration
569	operator--(int)
570	{ return duration(__r--); }
571
572	_GLIBCXX17_CONSTEXPR duration&
573	operator+=(const duration& __d)
574	{
575	  __r += __d.count();
576	  return *this;
577	}
578
579	_GLIBCXX17_CONSTEXPR duration&
580	operator-=(const duration& __d)
581	{
582	  __r -= __d.count();
583	  return *this;
584	}
585
586	_GLIBCXX17_CONSTEXPR duration&
587	operator*=(const rep& __rhs)
588	{
589	  __r *= __rhs;
590	  return *this;
591	}
592
593	_GLIBCXX17_CONSTEXPR duration&
594	operator/=(const rep& __rhs)
595	{
596	  __r /= __rhs;
597	  return *this;
598	}
599
600	// DR 934.
601	template<typename _Rep2 = rep>
602	  _GLIBCXX17_CONSTEXPR
603	  typename enable_if<!treat_as_floating_point<_Rep2>::value,
604			     duration&>::type
605	  operator%=(const rep& __rhs)
606	  {
607	    __r %= __rhs;
608	    return *this;
609	  }
610
611	template<typename _Rep2 = rep>
612	  _GLIBCXX17_CONSTEXPR
613	  typename enable_if<!treat_as_floating_point<_Rep2>::value,
614			     duration&>::type
615	  operator%=(const duration& __d)
616	  {
617	    __r %= __d.count();
618	    return *this;
619	  }
620
621	// 20.11.5.4 special values
622	static constexpr duration
623	zero() noexcept
624	{ return duration(duration_values<rep>::zero()); }
625
626	static constexpr duration
627	min() noexcept
628	{ return duration(duration_values<rep>::min()); }
629
630	static constexpr duration
631	max() noexcept
632	{ return duration(duration_values<rep>::max()); }
633
634      private:
635	rep __r;
636      };
637
638    /// @{
639    /// @relates std::chrono::duration
640
641    /// The sum of two durations.
642    template<typename _Rep1, typename _Period1,
643	     typename _Rep2, typename _Period2>
644      constexpr typename common_type<duration<_Rep1, _Period1>,
645				     duration<_Rep2, _Period2>>::type
646      operator+(const duration<_Rep1, _Period1>& __lhs,
647		const duration<_Rep2, _Period2>& __rhs)
648      {
649	typedef duration<_Rep1, _Period1>			__dur1;
650	typedef duration<_Rep2, _Period2>			__dur2;
651	typedef typename common_type<__dur1,__dur2>::type	__cd;
652	return __cd(__cd(__lhs).count() + __cd(__rhs).count());
653      }
654
655    /// The difference between two durations.
656    template<typename _Rep1, typename _Period1,
657	     typename _Rep2, typename _Period2>
658      constexpr typename common_type<duration<_Rep1, _Period1>,
659				     duration<_Rep2, _Period2>>::type
660      operator-(const duration<_Rep1, _Period1>& __lhs,
661		const duration<_Rep2, _Period2>& __rhs)
662      {
663	typedef duration<_Rep1, _Period1>			__dur1;
664	typedef duration<_Rep2, _Period2>			__dur2;
665	typedef typename common_type<__dur1,__dur2>::type	__cd;
666	return __cd(__cd(__lhs).count() - __cd(__rhs).count());
667      }
668
669    /// @}
670
671    /// @cond undocumented
672
673    // SFINAE helper to obtain common_type<_Rep1, _Rep2> only if _Rep2
674    // is implicitly convertible to it.
675    // _GLIBCXX_RESOLVE_LIB_DEFECTS
676    // 3050. Conversion specification problem in chrono::duration constructor
677    template<typename _Rep1, typename _Rep2,
678	     typename _CRep = typename common_type<_Rep1, _Rep2>::type>
679      using __common_rep_t = typename
680	enable_if<is_convertible<const _Rep2&, _CRep>::value, _CRep>::type;
681
682    /// @endcond
683
684    /** @{
685     * Arithmetic operators for chrono::duration
686     * @relates std::chrono::duration
687     */
688
689    template<typename _Rep1, typename _Period, typename _Rep2>
690      constexpr duration<__common_rep_t<_Rep1, _Rep2>, _Period>
691      operator*(const duration<_Rep1, _Period>& __d, const _Rep2& __s)
692      {
693	typedef duration<typename common_type<_Rep1, _Rep2>::type, _Period>
694	  __cd;
695	return __cd(__cd(__d).count() * __s);
696      }
697
698    template<typename _Rep1, typename _Rep2, typename _Period>
699      constexpr duration<__common_rep_t<_Rep2, _Rep1>, _Period>
700      operator*(const _Rep1& __s, const duration<_Rep2, _Period>& __d)
701      { return __d * __s; }
702
703    template<typename _Rep1, typename _Period, typename _Rep2>
704      constexpr
705      duration<__common_rep_t<_Rep1, __disable_if_is_duration<_Rep2>>, _Period>
706      operator/(const duration<_Rep1, _Period>& __d, const _Rep2& __s)
707      {
708	typedef duration<typename common_type<_Rep1, _Rep2>::type, _Period>
709	  __cd;
710	return __cd(__cd(__d).count() / __s);
711      }
712
713    template<typename _Rep1, typename _Period1,
714	     typename _Rep2, typename _Period2>
715      constexpr typename common_type<_Rep1, _Rep2>::type
716      operator/(const duration<_Rep1, _Period1>& __lhs,
717		const duration<_Rep2, _Period2>& __rhs)
718      {
719	typedef duration<_Rep1, _Period1>			__dur1;
720	typedef duration<_Rep2, _Period2>			__dur2;
721	typedef typename common_type<__dur1,__dur2>::type	__cd;
722	return __cd(__lhs).count() / __cd(__rhs).count();
723      }
724
725    // DR 934.
726    template<typename _Rep1, typename _Period, typename _Rep2>
727      constexpr
728      duration<__common_rep_t<_Rep1, __disable_if_is_duration<_Rep2>>, _Period>
729      operator%(const duration<_Rep1, _Period>& __d, const _Rep2& __s)
730      {
731	typedef duration<typename common_type<_Rep1, _Rep2>::type, _Period>
732	  __cd;
733	return __cd(__cd(__d).count() % __s);
734      }
735
736    template<typename _Rep1, typename _Period1,
737	     typename _Rep2, typename _Period2>
738      constexpr typename common_type<duration<_Rep1, _Period1>,
739				     duration<_Rep2, _Period2>>::type
740      operator%(const duration<_Rep1, _Period1>& __lhs,
741		const duration<_Rep2, _Period2>& __rhs)
742      {
743	typedef duration<_Rep1, _Period1>			__dur1;
744	typedef duration<_Rep2, _Period2>			__dur2;
745	typedef typename common_type<__dur1,__dur2>::type	__cd;
746	return __cd(__cd(__lhs).count() % __cd(__rhs).count());
747      }
748    /// @}
749
750    // comparisons
751
752    /** @{
753     * Comparisons for chrono::duration
754     * @relates std::chrono::duration
755     */
756
757    template<typename _Rep1, typename _Period1,
758	     typename _Rep2, typename _Period2>
759      constexpr bool
760      operator==(const duration<_Rep1, _Period1>& __lhs,
761		 const duration<_Rep2, _Period2>& __rhs)
762      {
763	typedef duration<_Rep1, _Period1>			__dur1;
764	typedef duration<_Rep2, _Period2>			__dur2;
765	typedef typename common_type<__dur1,__dur2>::type	__ct;
766	return __ct(__lhs).count() == __ct(__rhs).count();
767      }
768
769    template<typename _Rep1, typename _Period1,
770	     typename _Rep2, typename _Period2>
771      constexpr bool
772      operator<(const duration<_Rep1, _Period1>& __lhs,
773		const duration<_Rep2, _Period2>& __rhs)
774      {
775	typedef duration<_Rep1, _Period1>			__dur1;
776	typedef duration<_Rep2, _Period2>			__dur2;
777	typedef typename common_type<__dur1,__dur2>::type	__ct;
778	return __ct(__lhs).count() < __ct(__rhs).count();
779      }
780
781#if __cpp_lib_three_way_comparison
782    template<typename _Rep1, typename _Period1,
783	     typename _Rep2, typename _Period2>
784      requires three_way_comparable<common_type_t<_Rep1, _Rep2>>
785      constexpr auto
786      operator<=>(const duration<_Rep1, _Period1>& __lhs,
787		  const duration<_Rep2, _Period2>& __rhs)
788      {
789	using __ct = common_type_t<duration<_Rep1, _Period1>,
790				   duration<_Rep2, _Period2>>;
791	return __ct(__lhs).count() <=> __ct(__rhs).count();
792      }
793#else
794    template<typename _Rep1, typename _Period1,
795	     typename _Rep2, typename _Period2>
796      constexpr bool
797      operator!=(const duration<_Rep1, _Period1>& __lhs,
798		 const duration<_Rep2, _Period2>& __rhs)
799      { return !(__lhs == __rhs); }
800#endif
801
802    template<typename _Rep1, typename _Period1,
803	     typename _Rep2, typename _Period2>
804      constexpr bool
805      operator<=(const duration<_Rep1, _Period1>& __lhs,
806		 const duration<_Rep2, _Period2>& __rhs)
807      { return !(__rhs < __lhs); }
808
809    template<typename _Rep1, typename _Period1,
810	     typename _Rep2, typename _Period2>
811      constexpr bool
812      operator>(const duration<_Rep1, _Period1>& __lhs,
813		const duration<_Rep2, _Period2>& __rhs)
814      { return __rhs < __lhs; }
815
816    template<typename _Rep1, typename _Period1,
817	     typename _Rep2, typename _Period2>
818      constexpr bool
819      operator>=(const duration<_Rep1, _Period1>& __lhs,
820		 const duration<_Rep2, _Period2>& __rhs)
821      { return !(__lhs < __rhs); }
822
823    /// @}
824
825    /// @cond undocumented
826#ifdef _GLIBCXX_USE_C99_STDINT_TR1
827# define _GLIBCXX_CHRONO_INT64_T int64_t
828#elif defined __INT64_TYPE__
829# define _GLIBCXX_CHRONO_INT64_T __INT64_TYPE__
830#else
831    static_assert(std::numeric_limits<unsigned long long>::digits >= 64,
832	"Representation type for nanoseconds must have at least 64 bits");
833# define _GLIBCXX_CHRONO_INT64_T long long
834#endif
835    /// @endcond
836
837    /// nanoseconds
838    using nanoseconds	= duration<_GLIBCXX_CHRONO_INT64_T, nano>;
839
840    /// microseconds
841    using microseconds	= duration<_GLIBCXX_CHRONO_INT64_T, micro>;
842
843    /// milliseconds
844    using milliseconds	= duration<_GLIBCXX_CHRONO_INT64_T, milli>;
845
846    /// seconds
847    using seconds	= duration<_GLIBCXX_CHRONO_INT64_T>;
848
849    /// minutes
850    using minutes	= duration<_GLIBCXX_CHRONO_INT64_T, ratio< 60>>;
851
852    /// hours
853    using hours		= duration<_GLIBCXX_CHRONO_INT64_T, ratio<3600>>;
854
855#if __cplusplus > 201703L
856    /// days
857    using days		= duration<_GLIBCXX_CHRONO_INT64_T, ratio<86400>>;
858
859    /// weeks
860    using weeks		= duration<_GLIBCXX_CHRONO_INT64_T, ratio<604800>>;
861
862    /// years
863    using years		= duration<_GLIBCXX_CHRONO_INT64_T, ratio<31556952>>;
864
865    /// months
866    using months	= duration<_GLIBCXX_CHRONO_INT64_T, ratio<2629746>>;
867#endif // C++20
868
869#undef _GLIBCXX_CHRONO_INT64_T
870
871    template<typename _Clock, typename _Dur>
872      struct time_point
873      {
874	static_assert(__is_duration<_Dur>::value,
875	    "duration must be a specialization of std::chrono::duration");
876
877	typedef _Clock						clock;
878	typedef _Dur						duration;
879	typedef typename duration::rep				rep;
880	typedef typename duration::period			period;
881
882	constexpr time_point() : __d(duration::zero())
883	{ }
884
885	constexpr explicit time_point(const duration& __dur)
886	: __d(__dur)
887	{ }
888
889	// conversions
890	template<typename _Dur2,
891		 typename = _Require<is_convertible<_Dur2, _Dur>>>
892	  constexpr time_point(const time_point<clock, _Dur2>& __t)
893	  : __d(__t.time_since_epoch())
894	  { }
895
896	// observer
897	constexpr duration
898	time_since_epoch() const
899	{ return __d; }
900
901#if __cplusplus > 201703L
902	constexpr time_point&
903	operator++()
904	{
905	  ++__d;
906	  return *this;
907	}
908
909	constexpr time_point
910	operator++(int)
911	{ return time_point{__d++}; }
912
913	constexpr time_point&
914	operator--()
915	{
916	  --__d;
917	  return *this;
918	}
919
920	constexpr time_point
921	operator--(int)
922	{ return time_point{__d--}; }
923#endif
924
925	// arithmetic
926	_GLIBCXX17_CONSTEXPR time_point&
927	operator+=(const duration& __dur)
928	{
929	  __d += __dur;
930	  return *this;
931	}
932
933	_GLIBCXX17_CONSTEXPR time_point&
934	operator-=(const duration& __dur)
935	{
936	  __d -= __dur;
937	  return *this;
938	}
939
940	// special values
941	static constexpr time_point
942	min() noexcept
943	{ return time_point(duration::min()); }
944
945	static constexpr time_point
946	max() noexcept
947	{ return time_point(duration::max()); }
948
949      private:
950	duration __d;
951      };
952
953    /// time_point_cast
954    template<typename _ToDur, typename _Clock, typename _Dur>
955      constexpr typename enable_if<__is_duration<_ToDur>::value,
956				   time_point<_Clock, _ToDur>>::type
957      time_point_cast(const time_point<_Clock, _Dur>& __t)
958      {
959	typedef time_point<_Clock, _ToDur>			__time_point;
960	return __time_point(duration_cast<_ToDur>(__t.time_since_epoch()));
961      }
962
963#if __cplusplus > 201402L
964    template<typename _ToDur, typename _Clock, typename _Dur>
965      constexpr
966      enable_if_t<__is_duration<_ToDur>::value, time_point<_Clock, _ToDur>>
967      floor(const time_point<_Clock, _Dur>& __tp)
968      {
969	return time_point<_Clock, _ToDur>{
970	    chrono::floor<_ToDur>(__tp.time_since_epoch())};
971      }
972
973    template<typename _ToDur, typename _Clock, typename _Dur>
974      constexpr
975      enable_if_t<__is_duration<_ToDur>::value, time_point<_Clock, _ToDur>>
976      ceil(const time_point<_Clock, _Dur>& __tp)
977      {
978	return time_point<_Clock, _ToDur>{
979	    chrono::ceil<_ToDur>(__tp.time_since_epoch())};
980      }
981
982    template<typename _ToDur, typename _Clock, typename _Dur>
983      constexpr enable_if_t<
984	__and_<__is_duration<_ToDur>,
985	       __not_<treat_as_floating_point<typename _ToDur::rep>>>::value,
986	time_point<_Clock, _ToDur>>
987      round(const time_point<_Clock, _Dur>& __tp)
988      {
989	return time_point<_Clock, _ToDur>{
990	    chrono::round<_ToDur>(__tp.time_since_epoch())};
991      }
992#endif // C++17
993
994    /// @{
995    /// @relates time_point
996
997    /// Adjust a time point forwards by the given duration.
998    template<typename _Clock, typename _Dur1,
999	     typename _Rep2, typename _Period2>
1000      constexpr time_point<_Clock,
1001	typename common_type<_Dur1, duration<_Rep2, _Period2>>::type>
1002      operator+(const time_point<_Clock, _Dur1>& __lhs,
1003		const duration<_Rep2, _Period2>& __rhs)
1004      {
1005	typedef duration<_Rep2, _Period2>			__dur2;
1006	typedef typename common_type<_Dur1,__dur2>::type	__ct;
1007	typedef time_point<_Clock, __ct>			__time_point;
1008	return __time_point(__lhs.time_since_epoch() + __rhs);
1009      }
1010
1011    /// Adjust a time point forwards by the given duration.
1012    template<typename _Rep1, typename _Period1,
1013	     typename _Clock, typename _Dur2>
1014      constexpr time_point<_Clock,
1015	typename common_type<duration<_Rep1, _Period1>, _Dur2>::type>
1016      operator+(const duration<_Rep1, _Period1>& __lhs,
1017		const time_point<_Clock, _Dur2>& __rhs)
1018      {
1019	typedef duration<_Rep1, _Period1>			__dur1;
1020	typedef typename common_type<__dur1,_Dur2>::type	__ct;
1021	typedef time_point<_Clock, __ct>			__time_point;
1022	return __time_point(__rhs.time_since_epoch() + __lhs);
1023      }
1024
1025    /// Adjust a time point backwards by the given duration.
1026    template<typename _Clock, typename _Dur1,
1027	     typename _Rep2, typename _Period2>
1028      constexpr time_point<_Clock,
1029	typename common_type<_Dur1, duration<_Rep2, _Period2>>::type>
1030      operator-(const time_point<_Clock, _Dur1>& __lhs,
1031		const duration<_Rep2, _Period2>& __rhs)
1032      {
1033	typedef duration<_Rep2, _Period2>			__dur2;
1034	typedef typename common_type<_Dur1,__dur2>::type	__ct;
1035	typedef time_point<_Clock, __ct>			__time_point;
1036	return __time_point(__lhs.time_since_epoch() -__rhs);
1037      }
1038
1039    /// The difference between two time points (as a duration)
1040    template<typename _Clock, typename _Dur1, typename _Dur2>
1041      constexpr typename common_type<_Dur1, _Dur2>::type
1042      operator-(const time_point<_Clock, _Dur1>& __lhs,
1043		const time_point<_Clock, _Dur2>& __rhs)
1044      { return __lhs.time_since_epoch() - __rhs.time_since_epoch(); }
1045    /// @}
1046
1047    /** @{
1048     * Comparisons for time_point
1049     * @relates chrono::time_point
1050     */
1051
1052    template<typename _Clock, typename _Dur1, typename _Dur2>
1053      constexpr bool
1054      operator==(const time_point<_Clock, _Dur1>& __lhs,
1055		 const time_point<_Clock, _Dur2>& __rhs)
1056      { return __lhs.time_since_epoch() == __rhs.time_since_epoch(); }
1057
1058#if __cpp_lib_three_way_comparison
1059    template<typename _Clock, typename _Dur1,
1060	     three_way_comparable_with<_Dur1> _Dur2>
1061      constexpr auto
1062      operator<=>(const time_point<_Clock, _Dur1>& __lhs,
1063		  const time_point<_Clock, _Dur2>& __rhs)
1064      { return __lhs.time_since_epoch() <=> __rhs.time_since_epoch(); }
1065#else
1066    template<typename _Clock, typename _Dur1, typename _Dur2>
1067      constexpr bool
1068      operator!=(const time_point<_Clock, _Dur1>& __lhs,
1069		 const time_point<_Clock, _Dur2>& __rhs)
1070      { return !(__lhs == __rhs); }
1071#endif
1072
1073    template<typename _Clock, typename _Dur1, typename _Dur2>
1074      constexpr bool
1075      operator<(const time_point<_Clock, _Dur1>& __lhs,
1076		const time_point<_Clock, _Dur2>& __rhs)
1077      { return  __lhs.time_since_epoch() < __rhs.time_since_epoch(); }
1078
1079    template<typename _Clock, typename _Dur1, typename _Dur2>
1080      constexpr bool
1081      operator<=(const time_point<_Clock, _Dur1>& __lhs,
1082		 const time_point<_Clock, _Dur2>& __rhs)
1083      { return !(__rhs < __lhs); }
1084
1085    template<typename _Clock, typename _Dur1, typename _Dur2>
1086      constexpr bool
1087      operator>(const time_point<_Clock, _Dur1>& __lhs,
1088		const time_point<_Clock, _Dur2>& __rhs)
1089      { return __rhs < __lhs; }
1090
1091    template<typename _Clock, typename _Dur1, typename _Dur2>
1092      constexpr bool
1093      operator>=(const time_point<_Clock, _Dur1>& __lhs,
1094		 const time_point<_Clock, _Dur2>& __rhs)
1095      { return !(__lhs < __rhs); }
1096
1097    /// @}
1098
1099    // Clocks.
1100
1101    // Why nanosecond resolution as the default?
1102    // Why have std::system_clock always count in the highest
1103    // resolution (ie nanoseconds), even if on some OSes the low 3
1104    // or 9 decimal digits will be always zero? This allows later
1105    // implementations to change the system_clock::now()
1106    // implementation any time to provide better resolution without
1107    // changing function signature or units.
1108
1109    // To support the (forward) evolution of the library's defined
1110    // clocks, wrap inside inline namespace so that the current
1111    // defintions of system_clock, steady_clock, and
1112    // high_resolution_clock types are uniquely mangled. This way, new
1113    // code can use the latests clocks, while the library can contain
1114    // compatibility definitions for previous versions.  At some
1115    // point, when these clocks settle down, the inlined namespaces
1116    // can be removed.  XXX GLIBCXX_ABI Deprecated
1117    inline namespace _V2 {
1118
1119    /**
1120     *  @brief System clock.
1121     *
1122     *  Time returned represents wall time from the system-wide clock.
1123     *  @ingroup chrono
1124    */
1125    struct system_clock
1126    {
1127      typedef chrono::nanoseconds				duration;
1128      typedef duration::rep					rep;
1129      typedef duration::period					period;
1130      typedef chrono::time_point<system_clock, duration> 	time_point;
1131
1132      static_assert(system_clock::duration::min()
1133		    < system_clock::duration::zero(),
1134		    "a clock's minimum duration cannot be less than its epoch");
1135
1136      static constexpr bool is_steady = false;
1137
1138      static time_point
1139      now() noexcept;
1140
1141      // Map to C API
1142      static std::time_t
1143      to_time_t(const time_point& __t) noexcept
1144      {
1145	return std::time_t(duration_cast<chrono::seconds>
1146			   (__t.time_since_epoch()).count());
1147      }
1148
1149      static time_point
1150      from_time_t(std::time_t __t) noexcept
1151      {
1152	typedef chrono::time_point<system_clock, seconds>	__from;
1153	return time_point_cast<system_clock::duration>
1154	       (__from(chrono::seconds(__t)));
1155      }
1156    };
1157
1158
1159    /**
1160     *  @brief Monotonic clock
1161     *
1162     *  Time returned has the property of only increasing at a uniform rate.
1163     *  @ingroup chrono
1164    */
1165    struct steady_clock
1166    {
1167      typedef chrono::nanoseconds				duration;
1168      typedef duration::rep					rep;
1169      typedef duration::period					period;
1170      typedef chrono::time_point<steady_clock, duration>	time_point;
1171
1172      static constexpr bool is_steady = true;
1173
1174      static time_point
1175      now() noexcept;
1176    };
1177
1178
1179    /**
1180     *  @brief Highest-resolution clock
1181     *
1182     *  This is the clock "with the shortest tick period." Alias to
1183     *  std::system_clock until higher-than-nanosecond definitions
1184     *  become feasible.
1185     *  @ingroup chrono
1186    */
1187    using high_resolution_clock = system_clock;
1188
1189    } // end inline namespace _V2
1190
1191#if __cplusplus > 201703L
1192    template<typename _Duration>
1193      using sys_time = time_point<system_clock, _Duration>;
1194    using sys_seconds = sys_time<seconds>;
1195    using sys_days = sys_time<days>;
1196
1197    using file_clock = ::std::filesystem::__file_clock;
1198
1199    template<typename _Duration>
1200      using file_time = time_point<file_clock, _Duration>;
1201
1202    template<> struct is_clock<system_clock> : true_type { };
1203    template<> struct is_clock<steady_clock> : true_type { };
1204    template<> struct is_clock<file_clock> : true_type { };
1205
1206    template<> inline constexpr bool is_clock_v<system_clock> = true;
1207    template<> inline constexpr bool is_clock_v<steady_clock> = true;
1208    template<> inline constexpr bool is_clock_v<file_clock> = true;
1209
1210    struct local_t { };
1211    template<typename _Duration>
1212      using local_time = time_point<local_t, _Duration>;
1213    using local_seconds = local_time<seconds>;
1214    using local_days = local_time<days>;
1215
1216    class utc_clock;
1217    class tai_clock;
1218    class gps_clock;
1219
1220    template<typename _Duration>
1221      using utc_time = time_point<utc_clock, _Duration>;
1222    using utc_seconds = utc_time<seconds>;
1223
1224    template<typename _Duration>
1225      using tai_time = time_point<tai_clock, _Duration>;
1226    using tai_seconds = tai_time<seconds>;
1227
1228    template<typename _Duration>
1229      using gps_time = time_point<gps_clock, _Duration>;
1230    using gps_seconds = gps_time<seconds>;
1231
1232    template<> struct is_clock<utc_clock> : true_type { };
1233    template<> struct is_clock<tai_clock> : true_type { };
1234    template<> struct is_clock<gps_clock> : true_type { };
1235
1236    template<> inline constexpr bool is_clock_v<utc_clock> = true;
1237    template<> inline constexpr bool is_clock_v<tai_clock> = true;
1238    template<> inline constexpr bool is_clock_v<gps_clock> = true;
1239
1240    struct leap_second_info
1241    {
1242      bool is_leap_second;
1243      seconds elapsed;
1244    };
1245
1246    // CALENDRICAL TYPES
1247
1248    // CLASS DECLARATIONS
1249    class day;
1250    class month;
1251    class year;
1252    class weekday;
1253    class weekday_indexed;
1254    class weekday_last;
1255    class month_day;
1256    class month_day_last;
1257    class month_weekday;
1258    class month_weekday_last;
1259    class year_month;
1260    class year_month_day;
1261    class year_month_day_last;
1262    class year_month_weekday;
1263    class year_month_weekday_last;
1264
1265    struct last_spec
1266    {
1267      explicit last_spec() = default;
1268
1269      friend constexpr month_day_last
1270      operator/(int __m, last_spec) noexcept;
1271
1272      friend constexpr month_day_last
1273      operator/(last_spec, int __m) noexcept;
1274    };
1275
1276    inline constexpr last_spec last{};
1277
1278    namespace __detail
1279    {
1280      // Compute the remainder of the Euclidean division of __n divided by __d.
1281      // Euclidean division truncates toward negative infinity and always
1282      // produces a remainder in the range of [0,__d-1] (whereas standard
1283      // division truncates toward zero and yields a nonpositive remainder
1284      // for negative __n).
1285      constexpr unsigned
1286      __modulo(long long __n, unsigned __d)
1287      {
1288	if (__n >= 0)
1289	  return __n % __d;
1290	else
1291	  return (__d + (__n % __d)) % __d;
1292      }
1293
1294      inline constexpr unsigned __days_per_month[12]
1295	= { 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
1296    }
1297
1298    // DAY
1299
1300    class day
1301    {
1302    private:
1303      unsigned char _M_d;
1304
1305    public:
1306      day() = default;
1307
1308      explicit constexpr
1309      day(unsigned __d) noexcept
1310      : _M_d(__d)
1311      { }
1312
1313      constexpr day&
1314      operator++() noexcept
1315      {
1316	++_M_d;
1317	return *this;
1318      }
1319
1320      constexpr day
1321      operator++(int) noexcept
1322      {
1323	auto __ret = *this;
1324	++(*this);
1325	return __ret;
1326      }
1327
1328      constexpr day&
1329      operator--() noexcept
1330      {
1331	--_M_d;
1332	return *this;
1333      }
1334
1335      constexpr day
1336      operator--(int) noexcept
1337      {
1338	auto __ret = *this;
1339	--(*this);
1340	return __ret;
1341      }
1342
1343      constexpr day&
1344      operator+=(const days& __d) noexcept
1345      {
1346	*this = *this + __d;
1347	return *this;
1348      }
1349
1350      constexpr day&
1351      operator-=(const days& __d) noexcept
1352      {
1353	*this = *this - __d;
1354	return *this;
1355      }
1356
1357      constexpr explicit
1358      operator unsigned() const noexcept
1359      { return _M_d; }
1360
1361      constexpr bool
1362      ok() const noexcept
1363      { return 1 <= _M_d && _M_d <= 31; }
1364
1365      friend constexpr bool
1366      operator==(const day& __x, const day& __y) noexcept
1367      { return unsigned{__x} == unsigned{__y}; }
1368
1369      friend constexpr strong_ordering
1370      operator<=>(const day& __x, const day& __y) noexcept
1371      { return unsigned{__x} <=> unsigned{__y}; }
1372
1373      friend constexpr day
1374      operator+(const day& __x, const days& __y) noexcept
1375      { return day(unsigned{__x} + __y.count()); }
1376
1377      friend constexpr day
1378      operator+(const days& __x, const day& __y) noexcept
1379      { return __y + __x; }
1380
1381      friend constexpr day
1382      operator-(const day& __x, const days& __y) noexcept
1383      { return __x + -__y; }
1384
1385      friend constexpr days
1386      operator-(const day& __x, const day& __y) noexcept
1387      { return days{int(unsigned{__x}) - int(unsigned{__y})}; }
1388
1389      friend constexpr month_day
1390      operator/(const month& __m, const day& __d) noexcept;
1391
1392      friend constexpr month_day
1393      operator/(int __m, const day& __d) noexcept;
1394
1395      friend constexpr month_day
1396      operator/(const day& __d, const month& __m) noexcept;
1397
1398      friend constexpr month_day
1399      operator/(const day& __d, int __m) noexcept;
1400
1401      friend constexpr year_month_day
1402      operator/(const year_month& __ym, const day& __d) noexcept;
1403
1404      // TODO: Implement operator<<, to_stream, from_stream.
1405    };
1406
1407    // MONTH
1408
1409    class month
1410    {
1411    private:
1412      unsigned char _M_m;
1413
1414    public:
1415      month() = default;
1416
1417      explicit constexpr
1418      month(unsigned __m) noexcept
1419      : _M_m(__m)
1420      { }
1421
1422      constexpr month&
1423      operator++() noexcept
1424      {
1425	*this += months{1};
1426	return *this;
1427      }
1428
1429      constexpr month
1430      operator++(int) noexcept
1431      {
1432	auto __ret = *this;
1433	++(*this);
1434	return __ret;
1435      }
1436
1437      constexpr month&
1438      operator--() noexcept
1439      {
1440	*this -= months{1};
1441	return *this;
1442      }
1443
1444      constexpr month
1445      operator--(int) noexcept
1446      {
1447	auto __ret = *this;
1448	--(*this);
1449	return __ret;
1450      }
1451
1452      constexpr month&
1453      operator+=(const months& __m) noexcept
1454      {
1455	*this = *this + __m;
1456	return *this;
1457      }
1458
1459      constexpr month&
1460      operator-=(const months& __m) noexcept
1461      {
1462	*this = *this - __m;
1463	return *this;
1464      }
1465
1466      explicit constexpr
1467      operator unsigned() const noexcept
1468      { return _M_m; }
1469
1470      constexpr bool
1471      ok() const noexcept
1472      { return 1 <= _M_m && _M_m <= 12; }
1473
1474      friend constexpr bool
1475      operator==(const month& __x, const month& __y) noexcept
1476      { return unsigned{__x} == unsigned{__y}; }
1477
1478      friend constexpr strong_ordering
1479      operator<=>(const month& __x, const month& __y) noexcept
1480      { return unsigned{__x} <=> unsigned{__y}; }
1481
1482      friend constexpr month
1483      operator+(const month& __x, const months& __y) noexcept
1484      {
1485	auto __n = static_cast<long long>(unsigned{__x}) + (__y.count() - 1);
1486	return month{__detail::__modulo(__n, 12) + 1};
1487      }
1488
1489      friend constexpr month
1490      operator+(const months& __x,  const month& __y) noexcept
1491      { return __y + __x; }
1492
1493      friend constexpr month
1494      operator-(const month& __x, const months& __y) noexcept
1495      { return __x + -__y; }
1496
1497      friend constexpr months
1498      operator-(const month& __x,  const month& __y) noexcept
1499      {
1500	const auto __dm = int(unsigned(__x)) - int(unsigned(__y));
1501	return months{__dm < 0 ? 12 + __dm : __dm};
1502      }
1503
1504      friend constexpr year_month
1505      operator/(const year& __y, const month& __m) noexcept;
1506
1507      friend constexpr month_day
1508      operator/(const month& __m, int __d) noexcept;
1509
1510      friend constexpr month_day_last
1511      operator/(const month& __m, last_spec) noexcept;
1512
1513      friend constexpr month_day_last
1514      operator/(last_spec, const month& __m) noexcept;
1515
1516      friend constexpr month_weekday
1517      operator/(const month& __m, const weekday_indexed& __wdi) noexcept;
1518
1519      friend constexpr month_weekday
1520      operator/(const weekday_indexed& __wdi, const month& __m) noexcept;
1521
1522      friend constexpr month_weekday_last
1523      operator/(const month& __m, const weekday_last& __wdl) noexcept;
1524
1525      friend constexpr month_weekday_last
1526      operator/(const weekday_last& __wdl, const month& __m) noexcept;
1527
1528      // TODO: Implement operator<<, to_stream, from_stream.
1529    };
1530
1531    inline constexpr month January{1};
1532    inline constexpr month February{2};
1533    inline constexpr month March{3};
1534    inline constexpr month April{4};
1535    inline constexpr month May{5};
1536    inline constexpr month June{6};
1537    inline constexpr month July{7};
1538    inline constexpr month August{8};
1539    inline constexpr month September{9};
1540    inline constexpr month October{10};
1541    inline constexpr month November{11};
1542    inline constexpr month December{12};
1543
1544    // YEAR
1545
1546    class year
1547    {
1548    private:
1549      short _M_y;
1550
1551    public:
1552      year() = default;
1553
1554      explicit constexpr
1555      year(int __y) noexcept
1556      : _M_y{static_cast<short>(__y)}
1557      { }
1558
1559      static constexpr year
1560      min() noexcept
1561      { return year{-32767}; }
1562
1563      static constexpr year
1564      max() noexcept
1565      { return year{32767}; }
1566
1567      constexpr year&
1568      operator++() noexcept
1569      {
1570	++_M_y;
1571	return *this;
1572      }
1573
1574      constexpr year
1575      operator++(int) noexcept
1576      {
1577	auto __ret = *this;
1578	++(*this);
1579	return __ret;
1580      }
1581
1582      constexpr year&
1583      operator--() noexcept
1584      {
1585	--_M_y;
1586	return *this;
1587      }
1588
1589      constexpr year
1590      operator--(int) noexcept
1591      {
1592	auto __ret = *this;
1593	--(*this);
1594	return __ret;
1595      }
1596
1597      constexpr year&
1598      operator+=(const years& __y) noexcept
1599      {
1600	*this = *this + __y;
1601	return *this;
1602      }
1603
1604      constexpr year&
1605      operator-=(const years& __y) noexcept
1606      {
1607	*this = *this - __y;
1608	return *this;
1609      }
1610
1611      constexpr year
1612      operator+() const noexcept
1613      { return *this; }
1614
1615      constexpr year
1616      operator-() const noexcept
1617      { return year{-_M_y}; }
1618
1619      constexpr bool
1620      is_leap() const noexcept
1621      {
1622	// Testing divisibility by 100 first gives better performance, that is,
1623	// return (_M_y % 100 != 0 || _M_y % 400 == 0) && _M_y % 4 == 0;
1624
1625	// It gets even faster if _M_y is in [-536870800, 536870999]
1626	// (which is the case here) and _M_y % 100 is replaced by
1627	// __is_multiple_of_100 below.
1628
1629	// References:
1630	// [1] https://github.com/cassioneri/calendar
1631	// [2] https://accu.org/journals/overload/28/155/overload155.pdf#page=16
1632
1633	constexpr uint32_t __multiplier   = 42949673;
1634	constexpr uint32_t __bound        = 42949669;
1635	constexpr uint32_t __max_dividend = 1073741799;
1636	constexpr uint32_t __offset       = __max_dividend / 2 / 100 * 100;
1637	const bool __is_multiple_of_100
1638	  = __multiplier * (_M_y + __offset) < __bound;
1639	return (!__is_multiple_of_100 || _M_y % 400 == 0) && _M_y % 4 == 0;
1640      }
1641
1642      explicit constexpr
1643      operator int() const noexcept
1644      { return _M_y; }
1645
1646      constexpr bool
1647      ok() const noexcept
1648      { return min()._M_y <= _M_y && _M_y <= max()._M_y; }
1649
1650      friend constexpr bool
1651      operator==(const year& __x, const year& __y) noexcept
1652      { return int{__x} == int{__y}; }
1653
1654      friend constexpr strong_ordering
1655      operator<=>(const year& __x, const year& __y) noexcept
1656      { return int{__x} <=> int{__y}; }
1657
1658      friend constexpr year
1659      operator+(const year& __x, const years& __y) noexcept
1660      { return year{int{__x} + static_cast<int>(__y.count())}; }
1661
1662      friend constexpr year
1663      operator+(const years& __x, const year& __y) noexcept
1664      { return __y + __x; }
1665
1666      friend constexpr year
1667      operator-(const year& __x, const years& __y) noexcept
1668      { return __x + -__y; }
1669
1670      friend constexpr years
1671      operator-(const year& __x, const year& __y) noexcept
1672      { return years{int{__x} - int{__y}}; }
1673
1674      friend constexpr year_month
1675      operator/(const year& __y, int __m) noexcept;
1676
1677      friend constexpr year_month_day
1678      operator/(const year& __y, const month_day& __md) noexcept;
1679
1680      friend constexpr year_month_day
1681      operator/(const month_day& __md, const year& __y) noexcept;
1682
1683      friend constexpr year_month_day_last
1684      operator/(const year& __y, const month_day_last& __mdl) noexcept;
1685
1686      friend constexpr year_month_day_last
1687      operator/(const month_day_last& __mdl, const year& __y) noexcept;
1688
1689      friend constexpr year_month_weekday
1690      operator/(const year& __y, const month_weekday& __mwd) noexcept;
1691
1692      friend constexpr year_month_weekday
1693      operator/(const month_weekday& __mwd, const year& __y) noexcept;
1694
1695      friend constexpr year_month_weekday_last
1696      operator/(const year& __y, const month_weekday_last& __mwdl) noexcept;
1697
1698      friend constexpr year_month_weekday_last
1699      operator/(const month_weekday_last& __mwdl, const year& __y) noexcept;
1700
1701      // TODO: Implement operator<<, to_stream, from_stream.
1702    };
1703
1704    // WEEKDAY
1705
1706    class weekday
1707    {
1708    private:
1709      unsigned char _M_wd;
1710
1711      static constexpr weekday
1712      _S_from_days(const days& __d)
1713      {
1714	auto __n = __d.count();
1715	return weekday(__n >= -4 ? (__n + 4) % 7 : (__n + 5) % 7 + 6);
1716      }
1717
1718    public:
1719      weekday() = default;
1720
1721      explicit constexpr
1722      weekday(unsigned __wd) noexcept
1723      : _M_wd(__wd == 7 ? 0 : __wd) // __wd % 7 ?
1724      { }
1725
1726      constexpr
1727      weekday(const sys_days& __dp) noexcept
1728      : weekday{_S_from_days(__dp.time_since_epoch())}
1729      { }
1730
1731      explicit constexpr
1732      weekday(const local_days& __dp) noexcept
1733      : weekday{sys_days{__dp.time_since_epoch()}}
1734      { }
1735
1736      constexpr weekday&
1737      operator++() noexcept
1738      {
1739	*this += days{1};
1740	return *this;
1741      }
1742
1743      constexpr weekday
1744      operator++(int) noexcept
1745      {
1746	auto __ret = *this;
1747	++(*this);
1748	return __ret;
1749      }
1750
1751      constexpr weekday&
1752      operator--() noexcept
1753      {
1754	*this -= days{1};
1755	return *this;
1756      }
1757
1758      constexpr weekday
1759      operator--(int) noexcept
1760      {
1761	auto __ret = *this;
1762	--(*this);
1763	return __ret;
1764      }
1765
1766      constexpr weekday&
1767      operator+=(const days& __d) noexcept
1768      {
1769	*this = *this + __d;
1770	return *this;
1771      }
1772
1773      constexpr weekday&
1774      operator-=(const days& __d) noexcept
1775      {
1776	*this = *this - __d;
1777	return *this;
1778      }
1779
1780      constexpr unsigned
1781      c_encoding() const noexcept
1782      { return _M_wd; }
1783
1784      constexpr unsigned
1785      iso_encoding() const noexcept
1786      { return _M_wd == 0u ? 7u : _M_wd; }
1787
1788      constexpr bool
1789      ok() const noexcept
1790      { return _M_wd <= 6; }
1791
1792      constexpr weekday_indexed
1793      operator[](unsigned __index) const noexcept;
1794
1795      constexpr weekday_last
1796      operator[](last_spec) const noexcept;
1797
1798      friend constexpr bool
1799      operator==(const weekday& __x, const weekday& __y) noexcept
1800      { return __x._M_wd == __y._M_wd; }
1801
1802      friend constexpr weekday
1803      operator+(const weekday& __x, const days& __y) noexcept
1804      {
1805	auto __n = static_cast<long long>(__x._M_wd) + __y.count();
1806	return weekday{__detail::__modulo(__n, 7)};
1807      }
1808
1809      friend constexpr weekday
1810      operator+(const days& __x, const weekday& __y) noexcept
1811      { return __y + __x; }
1812
1813      friend constexpr weekday
1814      operator-(const weekday& __x, const days& __y) noexcept
1815      { return __x + -__y; }
1816
1817      friend constexpr days
1818      operator-(const weekday& __x, const weekday& __y) noexcept
1819      {
1820	auto __n = static_cast<long long>(__x._M_wd) - __y._M_wd;
1821	return days{__detail::__modulo(__n, 7)};
1822      }
1823
1824      // TODO: operator<<, from_stream.
1825    };
1826
1827    inline constexpr weekday Sunday{0};
1828    inline constexpr weekday Monday{1};
1829    inline constexpr weekday Tuesday{2};
1830    inline constexpr weekday Wednesday{3};
1831    inline constexpr weekday Thursday{4};
1832    inline constexpr weekday Friday{5};
1833    inline constexpr weekday Saturday{6};
1834
1835    // WEEKDAY_INDEXED
1836
1837    class weekday_indexed
1838    {
1839    private:
1840      chrono::weekday _M_wd;
1841      unsigned char _M_index;
1842
1843    public:
1844      weekday_indexed() = default;
1845
1846      constexpr
1847      weekday_indexed(const chrono::weekday& __wd, unsigned __index) noexcept
1848      : _M_wd(__wd), _M_index(__index)
1849      { }
1850
1851      constexpr chrono::weekday
1852      weekday() const noexcept
1853      { return _M_wd; }
1854
1855      constexpr unsigned
1856      index() const noexcept
1857      { return _M_index; };
1858
1859      constexpr bool
1860      ok() const noexcept
1861      { return _M_wd.ok() && 1 <= _M_index && _M_index <= 5; }
1862
1863      friend constexpr bool
1864      operator==(const weekday_indexed& __x, const weekday_indexed& __y) noexcept
1865      { return __x.weekday() == __y.weekday() && __x.index() == __y.index(); }
1866
1867      friend constexpr month_weekday
1868      operator/(const month& __m, const weekday_indexed& __wdi) noexcept;
1869
1870      friend constexpr month_weekday
1871      operator/(int __m, const weekday_indexed& __wdi) noexcept;
1872
1873      friend constexpr month_weekday
1874      operator/(const weekday_indexed& __wdi, const month& __m) noexcept;
1875
1876      friend constexpr month_weekday
1877      operator/(const weekday_indexed& __wdi, int __m) noexcept;
1878
1879      friend constexpr year_month_weekday
1880      operator/(const year_month& __ym, const weekday_indexed& __wdi) noexcept;
1881
1882      // TODO: Implement operator<<.
1883    };
1884
1885    constexpr weekday_indexed
1886    weekday::operator[](unsigned __index) const noexcept
1887    { return {*this, __index}; }
1888
1889    // WEEKDAY_LAST
1890
1891    class weekday_last
1892    {
1893    private:
1894      chrono::weekday _M_wd;
1895
1896    public:
1897      explicit constexpr
1898      weekday_last(const chrono::weekday& __wd) noexcept
1899      : _M_wd{__wd}
1900      { }
1901
1902      constexpr chrono::weekday
1903      weekday() const noexcept
1904      { return _M_wd; }
1905
1906      constexpr bool
1907      ok() const noexcept
1908      { return _M_wd.ok(); }
1909
1910      friend constexpr bool
1911      operator==(const weekday_last& __x, const weekday_last& __y) noexcept
1912      { return __x.weekday() == __y.weekday(); }
1913
1914      friend constexpr month_weekday_last
1915      operator/(int __m, const weekday_last& __wdl) noexcept;
1916
1917      friend constexpr month_weekday_last
1918      operator/(const weekday_last& __wdl, int __m) noexcept;
1919
1920      friend constexpr year_month_weekday_last
1921      operator/(const year_month& __ym, const weekday_last& __wdl) noexcept;
1922
1923      // TODO: Implement operator<<.
1924    };
1925
1926    constexpr weekday_last
1927    weekday::operator[](last_spec) const noexcept
1928    { return weekday_last{*this}; }
1929
1930    // MONTH_DAY
1931
1932    class month_day
1933    {
1934    private:
1935      chrono::month _M_m;
1936      chrono::day _M_d;
1937
1938    public:
1939      month_day() = default;
1940
1941      constexpr
1942      month_day(const chrono::month& __m, const chrono::day& __d) noexcept
1943      : _M_m{__m}, _M_d{__d}
1944      { }
1945
1946      constexpr chrono::month
1947      month() const noexcept
1948      { return _M_m; }
1949
1950      constexpr chrono::day
1951      day() const noexcept
1952      { return _M_d; }
1953
1954      constexpr bool
1955      ok() const noexcept
1956      {
1957	return _M_m.ok()
1958	  && 1u <= unsigned(_M_d)
1959	  && unsigned(_M_d) <= __detail::__days_per_month[unsigned(_M_m) - 1];
1960      }
1961
1962      friend constexpr bool
1963      operator==(const month_day& __x, const month_day& __y) noexcept
1964      { return __x.month() == __y.month() && __x.day() == __y.day(); }
1965
1966      friend constexpr strong_ordering
1967      operator<=>(const month_day& __x, const month_day& __y) noexcept
1968	= default;
1969
1970      friend constexpr month_day
1971      operator/(const chrono::month& __m, const chrono::day& __d) noexcept
1972      { return {__m, __d}; }
1973
1974      friend constexpr month_day
1975      operator/(const chrono::month& __m, int __d) noexcept
1976      { return {__m, chrono::day(unsigned(__d))}; }
1977
1978      friend constexpr month_day
1979      operator/(int __m, const chrono::day& __d) noexcept
1980      { return {chrono::month(unsigned(__m)), __d}; }
1981
1982      friend constexpr month_day
1983      operator/(const chrono::day& __d, const chrono::month& __m) noexcept
1984      { return {__m, __d}; }
1985
1986      friend constexpr month_day
1987      operator/(const chrono::day& __d, int __m) noexcept
1988      { return {chrono::month(unsigned(__m)), __d}; }
1989
1990      friend constexpr year_month_day
1991      operator/(int __y, const month_day& __md) noexcept;
1992
1993      friend constexpr year_month_day
1994      operator/(const month_day& __md, int __y) noexcept;
1995
1996      // TODO: Implement operator<<, from_stream.
1997    };
1998
1999    // MONTH_DAY_LAST
2000
2001    class month_day_last
2002    {
2003    private:
2004      chrono::month _M_m;
2005
2006    public:
2007      explicit constexpr
2008      month_day_last(const chrono::month& __m) noexcept
2009      : _M_m{__m}
2010      { }
2011
2012      constexpr chrono::month
2013      month() const noexcept
2014      { return _M_m; }
2015
2016      constexpr bool
2017      ok() const noexcept
2018      { return _M_m.ok(); }
2019
2020      friend constexpr bool
2021      operator==(const month_day_last& __x, const month_day_last& __y) noexcept
2022      { return __x.month() == __y.month(); }
2023
2024      friend constexpr strong_ordering
2025      operator<=>(const month_day_last& __x, const month_day_last& __y) noexcept
2026	= default;
2027
2028      friend constexpr month_day_last
2029      operator/(const chrono::month& __m, last_spec) noexcept
2030      { return month_day_last{__m}; }
2031
2032      friend constexpr month_day_last
2033      operator/(int __m, last_spec) noexcept
2034      { return chrono::month(unsigned(__m)) / last; }
2035
2036      friend constexpr month_day_last
2037      operator/(last_spec, const chrono::month& __m) noexcept
2038      { return __m / last; }
2039
2040      friend constexpr month_day_last
2041      operator/(last_spec, int __m) noexcept
2042      { return __m / last; }
2043
2044      friend constexpr year_month_day_last
2045      operator/(int __y, const month_day_last& __mdl) noexcept;
2046
2047      friend constexpr year_month_day_last
2048      operator/(const month_day_last& __mdl, int __y) noexcept;
2049
2050      // TODO: Implement operator<<.
2051    };
2052
2053    // MONTH_WEEKDAY
2054
2055    class month_weekday
2056    {
2057    private:
2058      chrono::month _M_m;
2059      chrono::weekday_indexed _M_wdi;
2060
2061    public:
2062      constexpr
2063      month_weekday(const chrono::month& __m,
2064		    const chrono::weekday_indexed& __wdi) noexcept
2065      : _M_m{__m}, _M_wdi{__wdi}
2066      { }
2067
2068      constexpr chrono::month
2069      month() const noexcept
2070      { return _M_m; }
2071
2072      constexpr chrono::weekday_indexed
2073      weekday_indexed() const noexcept
2074      { return _M_wdi; }
2075
2076      constexpr bool
2077      ok() const noexcept
2078      { return _M_m.ok() && _M_wdi.ok(); }
2079
2080      friend constexpr bool
2081      operator==(const month_weekday& __x, const month_weekday& __y) noexcept
2082      {
2083	return __x.month() == __y.month()
2084	  && __x.weekday_indexed() == __y.weekday_indexed();
2085      }
2086
2087      friend constexpr month_weekday
2088      operator/(const chrono::month& __m,
2089		const chrono::weekday_indexed& __wdi) noexcept
2090      { return {__m, __wdi}; }
2091
2092      friend constexpr month_weekday
2093      operator/(int __m, const chrono::weekday_indexed& __wdi) noexcept
2094      { return chrono::month(unsigned(__m)) / __wdi; }
2095
2096      friend constexpr month_weekday
2097      operator/(const chrono::weekday_indexed& __wdi,
2098		const chrono::month& __m) noexcept
2099      { return __m / __wdi; }
2100
2101      friend constexpr month_weekday
2102      operator/(const chrono::weekday_indexed& __wdi, int __m) noexcept
2103      { return __m / __wdi; }
2104
2105      friend constexpr year_month_weekday
2106      operator/(int __y, const month_weekday& __mwd) noexcept;
2107
2108      friend constexpr year_month_weekday
2109      operator/(const month_weekday& __mwd, int __y) noexcept;
2110
2111      // TODO: Implement operator<<.
2112    };
2113
2114    // MONTH_WEEKDAY_LAST
2115
2116    class month_weekday_last
2117    {
2118    private:
2119      chrono::month _M_m;
2120      chrono::weekday_last _M_wdl;
2121
2122    public:
2123      constexpr
2124      month_weekday_last(const chrono::month& __m,
2125			 const chrono::weekday_last& __wdl) noexcept
2126      :_M_m{__m}, _M_wdl{__wdl}
2127      { }
2128
2129      constexpr chrono::month
2130      month() const noexcept
2131      { return _M_m; }
2132
2133      constexpr chrono::weekday_last
2134      weekday_last() const noexcept
2135      { return _M_wdl; }
2136
2137      constexpr bool
2138      ok() const noexcept
2139      { return _M_m.ok() && _M_wdl.ok(); }
2140
2141      friend constexpr bool
2142      operator==(const month_weekday_last& __x,
2143		 const month_weekday_last& __y) noexcept
2144      {
2145	return __x.month() == __y.month()
2146	  && __x.weekday_last() == __y.weekday_last();
2147      }
2148
2149      friend constexpr month_weekday_last
2150      operator/(const chrono::month& __m,
2151		const chrono::weekday_last& __wdl) noexcept
2152      { return {__m, __wdl}; }
2153
2154      friend constexpr month_weekday_last
2155      operator/(int __m, const chrono::weekday_last& __wdl) noexcept
2156      { return chrono::month(unsigned(__m)) / __wdl; }
2157
2158      friend constexpr month_weekday_last
2159      operator/(const chrono::weekday_last& __wdl,
2160		const chrono::month& __m) noexcept
2161      { return __m / __wdl; }
2162
2163      friend constexpr month_weekday_last
2164      operator/(const chrono::weekday_last& __wdl, int __m) noexcept
2165      { return chrono::month(unsigned(__m)) / __wdl; }
2166
2167      friend constexpr year_month_weekday_last
2168      operator/(int __y, const month_weekday_last& __mwdl) noexcept;
2169
2170      friend constexpr year_month_weekday_last
2171      operator/(const month_weekday_last& __mwdl, int __y) noexcept;
2172
2173      // TODO: Implement operator<<.
2174    };
2175
2176    // YEAR_MONTH
2177
2178    namespace __detail
2179    {
2180      // [time.cal.ym], [time.cal.ymd], etc constrain the 'months'-based
2181      // addition/subtraction operator overloads like so:
2182      //
2183      //   Constraints: if the argument supplied by the caller for the months
2184      //   parameter is convertible to years, its implicit conversion sequence
2185      //   to years is worse than its implicit conversion sequence to months.
2186      //
2187      // We realize this constraint by templatizing the 'months'-based
2188      // overloads (using a dummy defaulted template parameter), so that
2189      // overload resolution doesn't select the 'months'-based overload unless
2190      // the implicit conversion sequence to 'months' is better than that to
2191      // 'years'.
2192      using __months_years_conversion_disambiguator = void;
2193    }
2194
2195    class year_month
2196    {
2197    private:
2198      chrono::year _M_y;
2199      chrono::month _M_m;
2200
2201    public:
2202      year_month() = default;
2203
2204      constexpr
2205      year_month(const chrono::year& __y, const chrono::month& __m) noexcept
2206      : _M_y{__y}, _M_m{__m}
2207      { }
2208
2209      constexpr chrono::year
2210      year() const noexcept
2211      { return _M_y; }
2212
2213      constexpr chrono::month
2214      month() const noexcept
2215      { return _M_m; }
2216
2217      template<typename = __detail::__months_years_conversion_disambiguator>
2218	constexpr year_month&
2219	operator+=(const months& __dm) noexcept
2220	{
2221	  *this = *this + __dm;
2222	  return *this;
2223	}
2224
2225      template<typename = __detail::__months_years_conversion_disambiguator>
2226	constexpr year_month&
2227	operator-=(const months& __dm) noexcept
2228	{
2229	  *this = *this - __dm;
2230	  return *this;
2231	}
2232
2233      constexpr year_month&
2234      operator+=(const years& __dy)  noexcept
2235      {
2236	*this = *this + __dy;
2237	return *this;
2238      }
2239
2240      constexpr year_month&
2241      operator-=(const years& __dy)  noexcept
2242      {
2243	*this = *this - __dy;
2244	return *this;
2245      }
2246
2247      constexpr bool
2248      ok() const noexcept
2249      { return _M_y.ok() && _M_m.ok(); }
2250
2251      friend constexpr bool
2252      operator==(const year_month& __x, const year_month& __y) noexcept
2253      { return __x.year() == __y.year() && __x.month() == __y.month(); }
2254
2255      friend constexpr strong_ordering
2256      operator<=>(const year_month& __x, const year_month& __y) noexcept
2257	= default;
2258
2259      template<typename = __detail::__months_years_conversion_disambiguator>
2260	friend constexpr year_month
2261	operator+(const year_month& __ym, const months& __dm) noexcept
2262	{
2263	  // TODO: Optimize?
2264	  auto __m = __ym.month() + __dm;
2265	  auto __i = int(unsigned(__ym.month())) - 1 + __dm.count();
2266	  auto __y = (__i < 0
2267		      ? __ym.year() + years{(__i - 11) / 12}
2268		      : __ym.year() + years{__i / 12});
2269	  return __y / __m;
2270	}
2271
2272      template<typename = __detail::__months_years_conversion_disambiguator>
2273	friend constexpr year_month
2274	operator+(const months& __dm, const year_month& __ym) noexcept
2275	{ return __ym + __dm; }
2276
2277      template<typename = __detail::__months_years_conversion_disambiguator>
2278	friend constexpr year_month
2279	operator-(const year_month& __ym, const months& __dm) noexcept
2280	{ return __ym + -__dm; }
2281
2282      friend constexpr months
2283      operator-(const year_month& __x, const year_month& __y) noexcept
2284      {
2285	return (__x.year() - __y.year()
2286		+ months{static_cast<int>(unsigned{__x.month()})
2287			 - static_cast<int>(unsigned{__y.month()})});
2288      }
2289
2290      friend constexpr year_month
2291      operator+(const year_month& __ym, const years& __dy) noexcept
2292      { return (__ym.year() + __dy) / __ym.month(); }
2293
2294      friend constexpr year_month
2295      operator+(const years& __dy, const year_month& __ym) noexcept
2296      { return __ym + __dy; }
2297
2298      friend constexpr year_month
2299      operator-(const year_month& __ym, const years& __dy) noexcept
2300      { return __ym + -__dy; }
2301
2302      friend constexpr year_month
2303      operator/(const chrono::year& __y, const chrono::month& __m) noexcept
2304      { return {__y, __m}; }
2305
2306      friend constexpr year_month
2307      operator/(const chrono::year& __y, int __m) noexcept
2308      { return {__y, chrono::month(unsigned(__m))}; }
2309
2310      friend constexpr year_month_day
2311      operator/(const year_month& __ym, int __d) noexcept;
2312
2313      friend constexpr year_month_day_last
2314      operator/(const year_month& __ym, last_spec) noexcept;
2315
2316      // TODO: Implement operator<<, from_stream.
2317    };
2318
2319    // YEAR_MONTH_DAY
2320
2321    class year_month_day
2322    {
2323    private:
2324      chrono::year _M_y;
2325      chrono::month _M_m;
2326      chrono::day _M_d;
2327
2328      static constexpr year_month_day _S_from_days(const days& __dp) noexcept;
2329
2330      constexpr days _M_days_since_epoch() const noexcept;
2331
2332    public:
2333      year_month_day() = default;
2334
2335      constexpr
2336      year_month_day(const chrono::year& __y, const chrono::month& __m,
2337		     const chrono::day& __d) noexcept
2338      : _M_y{__y}, _M_m{__m}, _M_d{__d}
2339      { }
2340
2341      constexpr
2342      year_month_day(const year_month_day_last& __ymdl) noexcept;
2343
2344      constexpr
2345      year_month_day(const sys_days& __dp) noexcept
2346      : year_month_day(_S_from_days(__dp.time_since_epoch()))
2347      { }
2348
2349      explicit constexpr
2350      year_month_day(const local_days& __dp) noexcept
2351      : year_month_day(sys_days{__dp.time_since_epoch()})
2352      { }
2353
2354      template<typename = __detail::__months_years_conversion_disambiguator>
2355	constexpr year_month_day&
2356	operator+=(const months& __m) noexcept
2357	{
2358	  *this = *this + __m;
2359	  return *this;
2360	}
2361
2362      template<typename = __detail::__months_years_conversion_disambiguator>
2363	constexpr year_month_day&
2364	operator-=(const months& __m) noexcept
2365	{
2366	  *this = *this - __m;
2367	  return *this;
2368	}
2369
2370      constexpr year_month_day&
2371      operator+=(const years& __y) noexcept
2372      {
2373	*this = *this + __y;
2374	return *this;
2375      }
2376
2377      constexpr year_month_day&
2378      operator-=(const years& __y) noexcept
2379      {
2380	*this = *this - __y;
2381	return *this;
2382      }
2383
2384      constexpr chrono::year
2385      year() const noexcept
2386      { return _M_y; }
2387
2388      constexpr chrono::month
2389      month() const noexcept
2390      { return _M_m; }
2391
2392      constexpr chrono::day
2393      day() const noexcept
2394      { return _M_d; }
2395
2396      constexpr
2397      operator sys_days() const noexcept
2398      { return sys_days{_M_days_since_epoch()}; }
2399
2400      explicit constexpr
2401      operator local_days() const noexcept
2402      { return local_days{sys_days{*this}.time_since_epoch()}; }
2403
2404      constexpr bool ok() const noexcept;
2405
2406      friend constexpr bool
2407      operator==(const year_month_day& __x, const year_month_day& __y) noexcept
2408      {
2409	return __x.year() == __y.year()
2410	  && __x.month() == __y.month()
2411	  && __x.day() == __y.day();
2412      }
2413
2414      friend constexpr strong_ordering
2415      operator<=>(const year_month_day& __x, const year_month_day& __y) noexcept
2416	= default;
2417
2418      template<typename = __detail::__months_years_conversion_disambiguator>
2419	friend constexpr year_month_day
2420	operator+(const year_month_day& __ymd, const months& __dm) noexcept
2421	{ return (__ymd.year() / __ymd.month() + __dm) / __ymd.day(); }
2422
2423      template<typename = __detail::__months_years_conversion_disambiguator>
2424	friend constexpr year_month_day
2425	operator+(const months& __dm, const year_month_day& __ymd) noexcept
2426	{ return __ymd + __dm; }
2427
2428      friend constexpr year_month_day
2429      operator+(const year_month_day& __ymd, const years& __dy) noexcept
2430      { return (__ymd.year() + __dy) / __ymd.month() / __ymd.day(); }
2431
2432      friend constexpr year_month_day
2433      operator+(const years& __dy, const year_month_day& __ymd) noexcept
2434      { return __ymd + __dy; }
2435
2436      template<typename = __detail::__months_years_conversion_disambiguator>
2437	friend constexpr year_month_day
2438	operator-(const year_month_day& __ymd, const months& __dm) noexcept
2439	{ return __ymd + -__dm; }
2440
2441      friend constexpr year_month_day
2442      operator-(const year_month_day& __ymd, const years& __dy) noexcept
2443      { return __ymd + -__dy; }
2444
2445      friend constexpr year_month_day
2446      operator/(const year_month& __ym, const chrono::day& __d) noexcept
2447      { return {__ym.year(), __ym.month(), __d}; }
2448
2449      friend constexpr year_month_day
2450      operator/(const year_month& __ym, int __d) noexcept
2451      { return __ym / chrono::day{unsigned(__d)}; }
2452
2453      friend constexpr year_month_day
2454      operator/(const chrono::year& __y, const month_day& __md) noexcept
2455      { return __y / __md.month() / __md.day(); }
2456
2457      friend constexpr year_month_day
2458      operator/(int __y, const month_day& __md) noexcept
2459      { return chrono::year{__y} / __md; }
2460
2461      friend constexpr year_month_day
2462      operator/(const month_day& __md, const chrono::year& __y) noexcept
2463      { return __y / __md; }
2464
2465      friend constexpr year_month_day
2466      operator/(const month_day& __md, int __y) noexcept
2467      { return chrono::year(__y) / __md; }
2468
2469      // TODO: Implement operator<<, from_stream.
2470    };
2471
2472    // Construct from days since 1970/01/01.
2473    // Proposition 6.3 of Neri and Schneider,
2474    // "Euclidean Affine Functions and Applications to Calendar Algorithms".
2475    // https://arxiv.org/abs/2102.06959
2476    constexpr year_month_day
2477    year_month_day::_S_from_days(const days& __dp) noexcept
2478    {
2479      constexpr auto __z2    = static_cast<uint32_t>(-1468000);
2480      constexpr auto __r2_e3 = static_cast<uint32_t>(536895458);
2481
2482      const auto __r0 = static_cast<uint32_t>(__dp.count()) + __r2_e3;
2483
2484      const auto __n1 = 4 * __r0 + 3;
2485      const auto __q1 = __n1 / 146097;
2486      const auto __r1 = __n1 % 146097 / 4;
2487
2488      constexpr auto __p32 = static_cast<uint64_t>(1) << 32;
2489      const auto __n2 = 4 * __r1 + 3;
2490      const auto __u2 = static_cast<uint64_t>(2939745) * __n2;
2491      const auto __q2 = static_cast<uint32_t>(__u2 / __p32);
2492      const auto __r2 = static_cast<uint32_t>(__u2 % __p32) / 2939745 / 4;
2493
2494      constexpr auto __p16 = static_cast<uint32_t>(1) << 16;
2495      const auto __n3 = 2141 * __r2 + 197913;
2496      const auto __q3 = __n3 / __p16;
2497      const auto __r3 = __n3 % __p16 / 2141;
2498
2499      const auto __y0 = 100 * __q1 + __q2;
2500      const auto __m0 = __q3;
2501      const auto __d0 = __r3;
2502
2503      const auto __j  = __r2 >= 306;
2504      const auto __y1 = __y0 + __j;
2505      const auto __m1 = __j ? __m0 - 12 : __m0;
2506      const auto __d1 = __d0 + 1;
2507
2508      return year_month_day{chrono::year{static_cast<int>(__y1 + __z2)},
2509			    chrono::month{__m1}, chrono::day{__d1}};
2510    }
2511
2512    // Days since 1970/01/01.
2513    // Proposition 6.2 of Neri and Schneider,
2514    // "Euclidean Affine Functions and Applications to Calendar Algorithms".
2515    // https://arxiv.org/abs/2102.06959
2516    constexpr days
2517    year_month_day::_M_days_since_epoch() const noexcept
2518    {
2519      auto constexpr __z2    = static_cast<uint32_t>(-1468000);
2520      auto constexpr __r2_e3 = static_cast<uint32_t>(536895458);
2521
2522      const auto __y1 = static_cast<uint32_t>(static_cast<int>(_M_y)) - __z2;
2523      const auto __m1 = static_cast<uint32_t>(static_cast<unsigned>(_M_m));
2524      const auto __d1 = static_cast<uint32_t>(static_cast<unsigned>(_M_d));
2525
2526      const auto __j  = static_cast<uint32_t>(__m1 < 3);
2527      const auto __y0 = __y1 - __j;
2528      const auto __m0 = __j ? __m1 + 12 : __m1;
2529      const auto __d0 = __d1 - 1;
2530
2531      const auto __q1 = __y0 / 100;
2532      const auto __yc = 1461 * __y0 / 4 - __q1 + __q1 / 4;
2533      const auto __mc = (979 *__m0 - 2919) / 32;
2534      const auto __dc = __d0;
2535
2536      return days{static_cast<int32_t>(__yc + __mc + __dc - __r2_e3)};
2537    }
2538
2539    // YEAR_MONTH_DAY_LAST
2540
2541    class year_month_day_last
2542    {
2543    private:
2544      chrono::year _M_y;
2545      chrono::month_day_last _M_mdl;
2546
2547    public:
2548      constexpr
2549      year_month_day_last(const chrono::year& __y,
2550			  const chrono::month_day_last& __mdl) noexcept
2551      : _M_y{__y}, _M_mdl{__mdl}
2552      { }
2553
2554      template<typename = __detail::__months_years_conversion_disambiguator>
2555	constexpr year_month_day_last&
2556	operator+=(const months& __m) noexcept
2557	{
2558	  *this = *this + __m;
2559	  return *this;
2560	}
2561
2562      template<typename = __detail::__months_years_conversion_disambiguator>
2563	constexpr year_month_day_last&
2564	operator-=(const months& __m) noexcept
2565	{
2566	  *this = *this - __m;
2567	  return *this;
2568	}
2569
2570      constexpr year_month_day_last&
2571      operator+=(const years& __y)  noexcept
2572      {
2573	*this = *this + __y;
2574	return *this;
2575      }
2576
2577      constexpr year_month_day_last&
2578      operator-=(const years& __y)  noexcept
2579      {
2580	*this = *this - __y;
2581	return *this;
2582      }
2583
2584      constexpr chrono::year
2585      year() const noexcept
2586      { return _M_y; }
2587
2588      constexpr chrono::month
2589      month() const noexcept
2590      { return _M_mdl.month(); }
2591
2592      constexpr chrono::month_day_last
2593      month_day_last() const noexcept
2594      { return _M_mdl; }
2595
2596      // Return A day representing the last day of this year, month pair.
2597      constexpr chrono::day
2598      day() const noexcept
2599      {
2600	const auto __m = static_cast<unsigned>(month());
2601
2602	// Excluding February, the last day of month __m is either 30 or 31 or,
2603	// in another words, it is 30 + b = 30 | b, where b is in {0, 1}.
2604
2605	// If __m in {1, 3, 4, 5, 6, 7}, then b is 1 if, and only if __m is odd.
2606	// Hence, b = __m & 1 = (__m ^ 0) & 1.
2607
2608	// If __m in {8, 9, 10, 11, 12}, then b is 1 if, and only if __m is even.
2609	// Hence, b = (__m ^ 1) & 1.
2610
2611	// Therefore, b = (__m ^ c) & 1, where c = 0, if __m < 8, or c = 1 if
2612	// __m >= 8, that is, c = __m >> 3.
2613
2614	// The above mathematically justifies this implementation whose
2615	// performance does not depend on look-up tables being on the L1 cache.
2616	return chrono::day{__m != 2 ? ((__m ^ (__m >> 3)) & 1) | 30
2617				    : _M_y.is_leap() ? 29 : 28};
2618      }
2619
2620      constexpr
2621      operator sys_days() const noexcept
2622      { return sys_days{year() / month() / day()}; }
2623
2624      explicit constexpr
2625      operator local_days() const noexcept
2626      { return local_days{sys_days{*this}.time_since_epoch()}; }
2627
2628      constexpr bool
2629      ok() const noexcept
2630      { return _M_y.ok() && _M_mdl.ok(); }
2631
2632      friend constexpr bool
2633      operator==(const year_month_day_last& __x,
2634		 const year_month_day_last& __y) noexcept
2635      {
2636	return __x.year() == __y.year()
2637	  && __x.month_day_last() == __y.month_day_last();
2638      }
2639
2640      friend constexpr strong_ordering
2641      operator<=>(const year_month_day_last& __x,
2642		  const year_month_day_last& __y) noexcept
2643	= default;
2644
2645      template<typename = __detail::__months_years_conversion_disambiguator>
2646	friend constexpr year_month_day_last
2647	operator+(const year_month_day_last& __ymdl,
2648		  const months& __dm) noexcept
2649	{ return (__ymdl.year() / __ymdl.month() + __dm) / last; }
2650
2651      template<typename = __detail::__months_years_conversion_disambiguator>
2652	friend constexpr year_month_day_last
2653	operator+(const months& __dm,
2654		  const year_month_day_last& __ymdl) noexcept
2655	{ return __ymdl + __dm; }
2656
2657      template<typename = __detail::__months_years_conversion_disambiguator>
2658	friend constexpr year_month_day_last
2659	operator-(const year_month_day_last& __ymdl,
2660		  const months& __dm) noexcept
2661	{ return __ymdl + -__dm; }
2662
2663      friend constexpr year_month_day_last
2664      operator+(const year_month_day_last& __ymdl,
2665		const years& __dy) noexcept
2666      { return {__ymdl.year() + __dy, __ymdl.month_day_last()}; }
2667
2668      friend constexpr year_month_day_last
2669      operator+(const years& __dy,
2670		const year_month_day_last& __ymdl) noexcept
2671      { return __ymdl + __dy; }
2672
2673      friend constexpr year_month_day_last
2674      operator-(const year_month_day_last& __ymdl,
2675		const years& __dy) noexcept
2676      { return __ymdl + -__dy; }
2677
2678      friend constexpr year_month_day_last
2679      operator/(const year_month& __ym, last_spec) noexcept
2680      { return {__ym.year(), chrono::month_day_last{__ym.month()}}; }
2681
2682      friend constexpr year_month_day_last
2683      operator/(const chrono::year& __y,
2684		const chrono::month_day_last& __mdl) noexcept
2685      { return {__y, __mdl}; }
2686
2687      friend constexpr year_month_day_last
2688      operator/(int __y, const chrono::month_day_last& __mdl) noexcept
2689      { return chrono::year(__y) / __mdl; }
2690
2691      friend constexpr year_month_day_last
2692      operator/(const chrono::month_day_last& __mdl,
2693		const chrono::year& __y) noexcept
2694      { return __y / __mdl; }
2695
2696      friend constexpr year_month_day_last
2697      operator/(const chrono::month_day_last& __mdl, int __y) noexcept
2698      { return chrono::year(__y) / __mdl; }
2699
2700      // TODO: Implement operator<<.
2701    };
2702
2703    // year_month_day ctor from year_month_day_last
2704    constexpr
2705    year_month_day::year_month_day(const year_month_day_last& __ymdl) noexcept
2706    : _M_y{__ymdl.year()}, _M_m{__ymdl.month()}, _M_d{__ymdl.day()}
2707    { }
2708
2709    constexpr bool
2710    year_month_day::ok() const noexcept
2711    {
2712      if (!_M_y.ok() || !_M_m.ok())
2713	return false;
2714      return chrono::day{1} <= _M_d && _M_d <= (_M_y / _M_m / last).day();
2715    }
2716
2717    // YEAR_MONTH_WEEKDAY
2718
2719    class year_month_weekday
2720    {
2721    private:
2722      chrono::year _M_y;
2723      chrono::month _M_m;
2724      chrono::weekday_indexed _M_wdi;
2725
2726      static constexpr year_month_weekday
2727      _S_from_sys_days(const sys_days& __dp)
2728      {
2729	year_month_day __ymd{__dp};
2730	chrono::weekday __wd{__dp};
2731	auto __index = __wd[(unsigned{__ymd.day()} - 1) / 7 + 1];
2732	return {__ymd.year(), __ymd.month(), __index};
2733      }
2734
2735    public:
2736      year_month_weekday() = default;
2737
2738      constexpr
2739      year_month_weekday(const chrono::year& __y, const chrono::month& __m,
2740			 const chrono::weekday_indexed& __wdi) noexcept
2741      : _M_y{__y}, _M_m{__m}, _M_wdi{__wdi}
2742      { }
2743
2744      constexpr
2745      year_month_weekday(const sys_days& __dp) noexcept
2746      : year_month_weekday{_S_from_sys_days(__dp)}
2747      { }
2748
2749      explicit constexpr
2750      year_month_weekday(const local_days& __dp) noexcept
2751      : year_month_weekday{sys_days{__dp.time_since_epoch()}}
2752      { }
2753
2754      template<typename = __detail::__months_years_conversion_disambiguator>
2755	constexpr year_month_weekday&
2756	operator+=(const months& __m) noexcept
2757	{
2758	  *this = *this + __m;
2759	  return *this;
2760	}
2761
2762      template<typename = __detail::__months_years_conversion_disambiguator>
2763	constexpr year_month_weekday&
2764	operator-=(const months& __m) noexcept
2765	{
2766	  *this = *this - __m;
2767	  return *this;
2768	}
2769
2770      constexpr year_month_weekday&
2771      operator+=(const years& __y) noexcept
2772      {
2773	*this = *this + __y;
2774	return *this;
2775      }
2776
2777      constexpr year_month_weekday&
2778      operator-=(const years& __y) noexcept
2779      {
2780	*this = *this - __y;
2781	return *this;
2782      }
2783
2784      constexpr chrono::year
2785      year() const noexcept
2786      { return _M_y; }
2787
2788      constexpr chrono::month
2789      month() const noexcept
2790      { return _M_m; }
2791
2792      constexpr chrono::weekday
2793      weekday() const noexcept
2794      { return _M_wdi.weekday(); }
2795
2796      constexpr unsigned
2797      index() const noexcept
2798      { return _M_wdi.index(); }
2799
2800      constexpr chrono::weekday_indexed
2801      weekday_indexed() const noexcept
2802      { return _M_wdi; }
2803
2804      constexpr
2805      operator sys_days() const noexcept
2806      {
2807	auto __d = sys_days{year() / month() / 1};
2808	return __d + (weekday() - chrono::weekday(__d)
2809		      + days{(static_cast<int>(index())-1)*7});
2810      }
2811
2812      explicit constexpr
2813      operator local_days() const noexcept
2814      { return local_days{sys_days{*this}.time_since_epoch()}; }
2815
2816      constexpr bool
2817      ok() const noexcept
2818      {
2819	if (!_M_y.ok() || !_M_m.ok() || !_M_wdi.ok())
2820	  return false;
2821	if (_M_wdi.index() <= 4)
2822	  return true;
2823	days __d = (_M_wdi.weekday()
2824		    - chrono::weekday{sys_days{_M_y / _M_m / 1}}
2825		    + days((_M_wdi.index()-1)*7 + 1));
2826	__glibcxx_assert(__d.count() >= 1);
2827	return __d.count() <= unsigned{(_M_y / _M_m / last).day()};
2828      }
2829
2830      friend constexpr bool
2831      operator==(const year_month_weekday& __x,
2832		 const year_month_weekday& __y) noexcept
2833      {
2834	return __x.year() == __y.year()
2835	  && __x.month() == __y.month()
2836	  && __x.weekday_indexed() == __y.weekday_indexed();
2837      }
2838
2839      template<typename = __detail::__months_years_conversion_disambiguator>
2840	friend constexpr year_month_weekday
2841	operator+(const year_month_weekday& __ymwd, const months& __dm) noexcept
2842	{
2843	  return ((__ymwd.year() / __ymwd.month() + __dm)
2844		  / __ymwd.weekday_indexed());
2845	}
2846
2847      template<typename = __detail::__months_years_conversion_disambiguator>
2848	friend constexpr year_month_weekday
2849	operator+(const months& __dm, const year_month_weekday& __ymwd) noexcept
2850	{ return __ymwd + __dm; }
2851
2852      friend constexpr year_month_weekday
2853      operator+(const year_month_weekday& __ymwd, const years& __dy) noexcept
2854      { return {__ymwd.year() + __dy, __ymwd.month(), __ymwd.weekday_indexed()}; }
2855
2856      friend constexpr year_month_weekday
2857      operator+(const years& __dy, const year_month_weekday& __ymwd) noexcept
2858      { return __ymwd + __dy; }
2859
2860      template<typename = __detail::__months_years_conversion_disambiguator>
2861	friend constexpr year_month_weekday
2862	operator-(const year_month_weekday& __ymwd, const months& __dm) noexcept
2863	{ return __ymwd + -__dm; }
2864
2865      friend constexpr year_month_weekday
2866      operator-(const year_month_weekday& __ymwd, const years& __dy) noexcept
2867      { return __ymwd + -__dy; }
2868
2869      friend constexpr year_month_weekday
2870      operator/(const year_month& __ym,
2871		const chrono::weekday_indexed& __wdi) noexcept
2872      { return {__ym.year(), __ym.month(), __wdi}; }
2873
2874      friend constexpr year_month_weekday
2875      operator/(const chrono::year& __y, const month_weekday& __mwd) noexcept
2876      { return {__y, __mwd.month(), __mwd.weekday_indexed()}; }
2877
2878      friend constexpr year_month_weekday
2879      operator/(int __y, const month_weekday& __mwd) noexcept
2880      { return chrono::year(__y) / __mwd; }
2881
2882      friend constexpr year_month_weekday
2883      operator/(const month_weekday& __mwd, const chrono::year& __y) noexcept
2884      { return __y / __mwd; }
2885
2886      friend constexpr year_month_weekday
2887      operator/(const month_weekday& __mwd, int __y) noexcept
2888      { return chrono::year(__y) / __mwd; }
2889
2890      // TODO: Implement operator<<.
2891    };
2892
2893    // YEAR_MONTH_WEEKDAY_LAST
2894
2895    class year_month_weekday_last
2896    {
2897    private:
2898      chrono::year _M_y;
2899      chrono::month _M_m;
2900      chrono::weekday_last _M_wdl;
2901
2902    public:
2903      constexpr
2904      year_month_weekday_last(const chrono::year& __y, const chrono::month& __m,
2905			      const chrono::weekday_last& __wdl) noexcept
2906      : _M_y{__y}, _M_m{__m}, _M_wdl{__wdl}
2907      { }
2908
2909      template<typename = __detail::__months_years_conversion_disambiguator>
2910	constexpr year_month_weekday_last&
2911	operator+=(const months& __m) noexcept
2912	{
2913	  *this = *this + __m;
2914	  return *this;
2915	}
2916
2917      template<typename = __detail::__months_years_conversion_disambiguator>
2918	constexpr year_month_weekday_last&
2919	operator-=(const months& __m) noexcept
2920	{
2921	  *this = *this - __m;
2922	  return *this;
2923	}
2924
2925      constexpr year_month_weekday_last&
2926      operator+=(const years& __y)  noexcept
2927      {
2928	*this = *this + __y;
2929	return *this;
2930      }
2931
2932      constexpr year_month_weekday_last&
2933      operator-=(const years& __y)  noexcept
2934      {
2935	*this = *this - __y;
2936	return *this;
2937      }
2938
2939      constexpr chrono::year
2940      year() const noexcept
2941      { return _M_y; }
2942
2943      constexpr chrono::month
2944      month() const noexcept
2945      { return _M_m; }
2946
2947      constexpr chrono::weekday
2948      weekday() const noexcept
2949      { return _M_wdl.weekday(); }
2950
2951      constexpr chrono::weekday_last
2952      weekday_last() const noexcept
2953      { return _M_wdl; }
2954
2955      constexpr
2956      operator sys_days() const noexcept
2957      {
2958	const auto __d = sys_days{_M_y / _M_m / last};
2959	return sys_days{(__d - (chrono::weekday{__d}
2960				- _M_wdl.weekday())).time_since_epoch()};
2961      }
2962
2963      explicit constexpr
2964      operator local_days() const noexcept
2965      { return local_days{sys_days{*this}.time_since_epoch()}; }
2966
2967      constexpr bool
2968      ok() const noexcept
2969      { return _M_y.ok() && _M_m.ok() && _M_wdl.ok(); }
2970
2971      friend constexpr bool
2972      operator==(const year_month_weekday_last& __x,
2973		 const year_month_weekday_last& __y) noexcept
2974      {
2975	return __x.year() == __y.year()
2976	  && __x.month() == __y.month()
2977	  && __x.weekday_last() == __y.weekday_last();
2978      }
2979
2980      template<typename = __detail::__months_years_conversion_disambiguator>
2981	friend constexpr year_month_weekday_last
2982	operator+(const year_month_weekday_last& __ymwdl,
2983		  const months& __dm) noexcept
2984	{
2985	  return ((__ymwdl.year() / __ymwdl.month() + __dm)
2986		  / __ymwdl.weekday_last());
2987	}
2988
2989      template<typename = __detail::__months_years_conversion_disambiguator>
2990	friend constexpr year_month_weekday_last
2991	operator+(const months& __dm,
2992		  const year_month_weekday_last& __ymwdl) noexcept
2993	{ return __ymwdl + __dm; }
2994
2995      friend constexpr year_month_weekday_last
2996      operator+(const year_month_weekday_last& __ymwdl,
2997		const years& __dy) noexcept
2998      { return {__ymwdl.year() + __dy, __ymwdl.month(), __ymwdl.weekday_last()}; }
2999
3000      friend constexpr year_month_weekday_last
3001      operator+(const years& __dy,
3002		const year_month_weekday_last& __ymwdl) noexcept
3003      { return __ymwdl + __dy; }
3004
3005      template<typename = __detail::__months_years_conversion_disambiguator>
3006	friend constexpr year_month_weekday_last
3007	operator-(const year_month_weekday_last& __ymwdl,
3008		  const months& __dm) noexcept
3009	{ return __ymwdl + -__dm; }
3010
3011      friend constexpr year_month_weekday_last
3012      operator-(const year_month_weekday_last& __ymwdl,
3013		const years& __dy) noexcept
3014      { return __ymwdl + -__dy; }
3015
3016      friend constexpr year_month_weekday_last
3017      operator/(const year_month& __ym,
3018		const chrono::weekday_last& __wdl) noexcept
3019      { return {__ym.year(), __ym.month(), __wdl}; }
3020
3021      friend constexpr year_month_weekday_last
3022      operator/(const chrono::year& __y,
3023		const chrono::month_weekday_last& __mwdl) noexcept
3024      { return {__y, __mwdl.month(), __mwdl.weekday_last()}; }
3025
3026      friend constexpr year_month_weekday_last
3027      operator/(int __y, const chrono::month_weekday_last& __mwdl) noexcept
3028      { return chrono::year(__y) / __mwdl; }
3029
3030      friend constexpr year_month_weekday_last
3031      operator/(const chrono::month_weekday_last& __mwdl,
3032		const chrono::year& __y) noexcept
3033      { return __y / __mwdl; }
3034
3035      friend constexpr year_month_weekday_last
3036      operator/(const chrono::month_weekday_last& __mwdl, int __y) noexcept
3037      { return chrono::year(__y) / __mwdl; }
3038
3039      // TODO: Implement operator<<.
3040    };
3041
3042    // HH_MM_SS
3043
3044    namespace __detail
3045    {
3046      consteval long long
3047      __pow10(unsigned __n)
3048      {
3049	long long __r = 1;
3050	while (__n-- > 0)
3051	  __r *= 10;
3052	return __r;
3053      }
3054    }
3055
3056    template<typename _Duration>
3057      class hh_mm_ss
3058      {
3059      private:
3060	static constexpr int
3061	_S_fractional_width()
3062	{
3063	  int __multiplicity_2 = 0;
3064	  int __multiplicity_5 = 0;
3065	  auto __den = _Duration::period::den;
3066	  while ((__den % 2) == 0)
3067	    {
3068	      ++__multiplicity_2;
3069	      __den /= 2;
3070	    }
3071	  while ((__den % 5) == 0)
3072	    {
3073	      ++__multiplicity_5;
3074	      __den /= 5;
3075	    }
3076	  if (__den != 1)
3077	    return 6;
3078
3079	  int __width = (__multiplicity_2 > __multiplicity_5
3080			 ? __multiplicity_2 : __multiplicity_5);
3081	  if (__width > 18)
3082	    __width = 18;
3083	  return __width;
3084	}
3085
3086      public:
3087	static constexpr unsigned fractional_width = {_S_fractional_width()};
3088
3089	using precision
3090	  = duration<common_type_t<typename _Duration::rep,
3091				   chrono::seconds::rep>,
3092		     ratio<1, __detail::__pow10(fractional_width)>>;
3093
3094	constexpr
3095	hh_mm_ss() noexcept
3096	: hh_mm_ss{_Duration::zero()}
3097	{ }
3098
3099	constexpr explicit
3100	hh_mm_ss(_Duration __d) noexcept
3101	: _M_is_neg (__d < _Duration::zero()),
3102	  _M_h (duration_cast<chrono::hours>(abs(__d))),
3103	  _M_m (duration_cast<chrono::minutes>(abs(__d) - hours())),
3104	  _M_s (duration_cast<chrono::seconds>(abs(__d) - hours() - minutes()))
3105	{
3106	  if constexpr (treat_as_floating_point_v<typename precision::rep>)
3107	    _M_ss = abs(__d) - hours() - minutes() - seconds();
3108	  else
3109	    _M_ss = duration_cast<precision>(abs(__d) - hours()
3110					     - minutes() - seconds());
3111	}
3112
3113	constexpr bool
3114	is_negative() const noexcept
3115	{ return _M_is_neg; }
3116
3117	constexpr chrono::hours
3118	hours() const noexcept
3119	{ return _M_h; }
3120
3121	constexpr chrono::minutes
3122	minutes() const noexcept
3123	{ return _M_m; }
3124
3125	constexpr chrono::seconds
3126	seconds() const noexcept
3127	{ return _M_s; }
3128
3129	constexpr precision
3130	subseconds() const noexcept
3131	{ return _M_ss; }
3132
3133	constexpr explicit
3134	operator precision() const noexcept
3135	{ return to_duration(); }
3136
3137	constexpr precision
3138	to_duration() const noexcept
3139	{
3140	  if (_M_is_neg)
3141	    return -(_M_h + _M_m + _M_s + _M_ss);
3142	  else
3143	    return _M_h + _M_m + _M_s + _M_ss;
3144	}
3145
3146	// TODO: Implement operator<<.
3147
3148      private:
3149	bool _M_is_neg;
3150	chrono::hours _M_h;
3151	chrono::minutes _M_m;
3152	chrono::seconds _M_s;
3153	precision _M_ss;
3154      };
3155#endif // C++20
3156
3157    /// @} group chrono
3158  } // namespace chrono
3159
3160#if __cplusplus > 201103L
3161
3162#define __cpp_lib_chrono_udls 201304
3163
3164  inline namespace literals
3165  {
3166  /** ISO C++ 2014  namespace for suffixes for duration literals.
3167   *
3168   * These suffixes can be used to create `chrono::duration` values with
3169   * tick periods of hours, minutes, seconds, milliseconds, microseconds
3170   * or nanoseconds. For example, `std::chrono::seconds(5)` can be written
3171   * as `5s` after making the suffix visible in the current scope.
3172   * The suffixes can be made visible by a using-directive or
3173   * using-declaration such as:
3174   *  - `using namespace std::chrono_literals;`
3175   *  - `using namespace std::literals;`
3176   *  - `using namespace std::chrono;`
3177   *  - `using namespace std;`
3178   *  - `using std::chrono_literals::operator""s;`
3179   *
3180   * The result of these suffixes on an integer literal is one of the
3181   * standard typedefs such as `std::chrono::hours`.
3182   * The result on a floating-point literal is a duration type with the
3183   * specified tick period and an unspecified floating-point representation,
3184   * for example `1.5e2ms` might be equivalent to
3185   * `chrono::duration<long double, chrono::milli>(1.5e2)`.
3186   *
3187   * @ingroup chrono
3188   */
3189  inline namespace chrono_literals
3190  {
3191    /// @addtogroup chrono
3192    /// @{
3193
3194#pragma GCC diagnostic push
3195#pragma GCC diagnostic ignored "-Wliteral-suffix"
3196    /// @cond undocumented
3197    template<typename _Dur, char... _Digits>
3198      constexpr _Dur __check_overflow()
3199      {
3200	using _Val = __parse_int::_Parse_int<_Digits...>;
3201	constexpr typename _Dur::rep __repval = _Val::value;
3202	static_assert(__repval >= 0 && __repval == _Val::value,
3203		      "literal value cannot be represented by duration type");
3204	return _Dur(__repval);
3205      }
3206    /// @endcond
3207
3208    /// Literal suffix for durations representing non-integer hours
3209    constexpr chrono::duration<long double, ratio<3600,1>>
3210    operator""h(long double __hours)
3211    { return chrono::duration<long double, ratio<3600,1>>{__hours}; }
3212
3213    /// Literal suffix for durations of type `std::chrono::hours`
3214    template <char... _Digits>
3215      constexpr chrono::hours
3216      operator""h()
3217      { return __check_overflow<chrono::hours, _Digits...>(); }
3218
3219    /// Literal suffix for durations representing non-integer minutes
3220    constexpr chrono::duration<long double, ratio<60,1>>
3221    operator""min(long double __mins)
3222    { return chrono::duration<long double, ratio<60,1>>{__mins}; }
3223
3224    /// Literal suffix for durations of type `std::chrono::minutes`
3225    template <char... _Digits>
3226      constexpr chrono::minutes
3227      operator""min()
3228      { return __check_overflow<chrono::minutes, _Digits...>(); }
3229
3230    /// Literal suffix for durations representing non-integer seconds
3231    constexpr chrono::duration<long double>
3232    operator""s(long double __secs)
3233    { return chrono::duration<long double>{__secs}; }
3234
3235    /// Literal suffix for durations of type `std::chrono::seconds`
3236    template <char... _Digits>
3237      constexpr chrono::seconds
3238      operator""s()
3239      { return __check_overflow<chrono::seconds, _Digits...>(); }
3240
3241    /// Literal suffix for durations representing non-integer milliseconds
3242    constexpr chrono::duration<long double, milli>
3243    operator""ms(long double __msecs)
3244    { return chrono::duration<long double, milli>{__msecs}; }
3245
3246    /// Literal suffix for durations of type `std::chrono::milliseconds`
3247    template <char... _Digits>
3248      constexpr chrono::milliseconds
3249      operator""ms()
3250      { return __check_overflow<chrono::milliseconds, _Digits...>(); }
3251
3252    /// Literal suffix for durations representing non-integer microseconds
3253    constexpr chrono::duration<long double, micro>
3254    operator""us(long double __usecs)
3255    { return chrono::duration<long double, micro>{__usecs}; }
3256
3257    /// Literal suffix for durations of type `std::chrono::microseconds`
3258    template <char... _Digits>
3259      constexpr chrono::microseconds
3260      operator""us()
3261      { return __check_overflow<chrono::microseconds, _Digits...>(); }
3262
3263    /// Literal suffix for durations representing non-integer nanoseconds
3264    constexpr chrono::duration<long double, nano>
3265    operator""ns(long double __nsecs)
3266    { return chrono::duration<long double, nano>{__nsecs}; }
3267
3268    /// Literal suffix for durations of type `std::chrono::nanoseconds`
3269    template <char... _Digits>
3270      constexpr chrono::nanoseconds
3271      operator""ns()
3272      { return __check_overflow<chrono::nanoseconds, _Digits...>(); }
3273
3274#if __cplusplus > 201703L
3275    constexpr chrono::day
3276    operator""d(unsigned long long __d) noexcept
3277    { return chrono::day{static_cast<unsigned>(__d)}; }
3278
3279    constexpr chrono::year
3280    operator""y(unsigned long long __y) noexcept
3281    { return chrono::year{static_cast<int>(__y)}; }
3282#endif // C++20
3283
3284#pragma GCC diagnostic pop
3285    /// @}
3286  } // inline namespace chrono_literals
3287  } // inline namespace literals
3288
3289  namespace chrono
3290  {
3291    using namespace literals::chrono_literals;
3292  } // namespace chrono
3293
3294#if __cplusplus > 201703L
3295  namespace chrono
3296  {
3297    /// @addtogroup chrono
3298    /// @{
3299
3300    // 12/24 HOURS FUNCTIONS
3301
3302    constexpr bool
3303    is_am(const hours& __h) noexcept
3304    { return 0h <= __h && __h <= 11h; }
3305
3306    constexpr bool
3307    is_pm(const hours& __h) noexcept
3308    { return 12h <= __h && __h <= 23h; }
3309
3310    constexpr hours
3311    make12(const hours& __h) noexcept
3312    {
3313      if (__h == 0h)
3314	return 12h;
3315      else if (__h > 12h)
3316	return __h - 12h;
3317      return __h;
3318    }
3319
3320    constexpr hours
3321    make24(const hours& __h, bool __is_pm) noexcept
3322    {
3323      if (!__is_pm)
3324	{
3325	  if (__h == 12h)
3326	    return 0h;
3327	  else
3328	    return __h;
3329	}
3330      else
3331	{
3332	  if (__h == 12h)
3333	    return __h;
3334	  else
3335	    return __h + 12h;
3336	}
3337    }
3338    /// @} group chrono
3339  } // namespace chrono
3340#endif
3341
3342#if __cplusplus >= 201703L
3343  namespace filesystem
3344  {
3345    struct __file_clock
3346    {
3347      using duration                  = chrono::nanoseconds;
3348      using rep                       = duration::rep;
3349      using period                    = duration::period;
3350      using time_point                = chrono::time_point<__file_clock>;
3351      static constexpr bool is_steady = false;
3352
3353      static time_point
3354      now() noexcept
3355      { return _S_from_sys(chrono::system_clock::now()); }
3356
3357#if __cplusplus > 201703L
3358      template<typename _Dur>
3359	static
3360	chrono::file_time<_Dur>
3361	from_sys(const chrono::sys_time<_Dur>& __t) noexcept
3362	{ return _S_from_sys(__t); }
3363
3364      // For internal use only
3365      template<typename _Dur>
3366	static
3367	chrono::sys_time<_Dur>
3368	to_sys(const chrono::file_time<_Dur>& __t) noexcept
3369	{ return _S_to_sys(__t); }
3370#endif // C++20
3371
3372    private:
3373      using __sys_clock = chrono::system_clock;
3374
3375      // This clock's (unspecified) epoch is 2174-01-01 00:00:00 UTC.
3376      // A signed 64-bit duration with nanosecond resolution gives roughly
3377      // +/- 292 years, which covers the 1901-2446 date range for ext4.
3378      static constexpr chrono::seconds _S_epoch_diff{6437664000};
3379
3380    protected:
3381      // For internal use only
3382      template<typename _Dur>
3383	static
3384	chrono::time_point<__file_clock, _Dur>
3385	_S_from_sys(const chrono::time_point<__sys_clock, _Dur>& __t) noexcept
3386	{
3387	  using __file_time = chrono::time_point<__file_clock, _Dur>;
3388	  return __file_time{__t.time_since_epoch()} - _S_epoch_diff;
3389	}
3390
3391      // For internal use only
3392      template<typename _Dur>
3393	static
3394	chrono::time_point<__sys_clock, _Dur>
3395	_S_to_sys(const chrono::time_point<__file_clock, _Dur>& __t) noexcept
3396	{
3397	  using __sys_time = chrono::time_point<__sys_clock, _Dur>;
3398	  return __sys_time{__t.time_since_epoch()} + _S_epoch_diff;
3399	}
3400    };
3401  } // namespace filesystem
3402#endif // C++17
3403#endif // C++14
3404
3405_GLIBCXX_END_NAMESPACE_VERSION
3406} // namespace std
3407
3408#endif // C++11
3409
3410#endif //_GLIBCXX_CHRONO
3411