libstdc++-v3/include/std/chrono

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