chrono

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// <chrono> -*- C++ -*-

// Copyright (C) 2008-2022 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file include/chrono
 *  This is a Standard C++ Library header.
 *  @ingroup chrono
 */

#ifndef _GLIBCXX_CHRONO
#define _GLIBCXX_CHRONO 1

#pragma GCC system_header

#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else

#include <bits/chrono.h>
#if __cplusplus > 201703L
# include <sstream> // ostringstream
# include <bits/charconv.h>
#endif

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   * @defgroup chrono Time
   * @ingroup utilities
   *
   * Classes and functions for time.
   *
   * @since C++11
   */

  /** @namespace std::chrono
   *  @brief ISO C++ 2011 namespace for date and time utilities
   *  @ingroup chrono
   */
  namespace chrono
  {
#if __cplusplus >= 202002L
    /// @addtogroup chrono
    /// @{
    struct local_t { };
    template<typename _Duration>
      using local_time = time_point<local_t, _Duration>;
    using local_seconds = local_time<seconds>;
    using local_days = local_time<days>;

    class utc_clock;
    class tai_clock;
    class gps_clock;

    template<typename _Duration>
      using utc_time = time_point<utc_clock, _Duration>;
    using utc_seconds = utc_time<seconds>;

    template<typename _Duration>
      using tai_time = time_point<tai_clock, _Duration>;
    using tai_seconds = tai_time<seconds>;

    template<typename _Duration>
      using gps_time = time_point<gps_clock, _Duration>;
    using gps_seconds = gps_time<seconds>;

    template<> struct is_clock<utc_clock> : true_type { };
    template<> struct is_clock<tai_clock> : true_type { };
    template<> struct is_clock<gps_clock> : true_type { };

    template<> inline constexpr bool is_clock_v<utc_clock> = true;
    template<> inline constexpr bool is_clock_v<tai_clock> = true;
    template<> inline constexpr bool is_clock_v<gps_clock> = true;

    struct leap_second_info
    {
      bool is_leap_second;
      seconds elapsed;
    };

    // CALENDRICAL TYPES

    // CLASS DECLARATIONS
    class day;
    class month;
    class year;
    class weekday;
    class weekday_indexed;
    class weekday_last;
    class month_day;
    class month_day_last;
    class month_weekday;
    class month_weekday_last;
    class year_month;
    class year_month_day;
    class year_month_day_last;
    class year_month_weekday;
    class year_month_weekday_last;

    struct last_spec
    {
      explicit last_spec() = default;

      friend constexpr month_day_last
      operator/(int __m, last_spec) noexcept;

      friend constexpr month_day_last
      operator/(last_spec, int __m) noexcept;
    };

    inline constexpr last_spec last{};

    namespace __detail
    {
      // Helper to __add_modulo and __sub_modulo.
      template <unsigned __d, typename _Tp>
      consteval auto
      __modulo_offset()
      {
   using _Up = make_unsigned_t<_Tp>;
   auto constexpr __a = _Up(-1) - _Up(255 + __d - 2);
   auto constexpr __b = _Up(__d * (__a / __d) - 1);
   // Notice: b <= a - 1 <= _Up(-1) - (255 + d - 1) and b % d = d - 1.
   return _Up(-1) - __b; // >= 255 + d - 1
      }

      // Compute the remainder of the Euclidean division of __x + __y divided by
      // __d without overflowing.  Typically, __x <= 255 + d - 1 is sum of
      // weekday/month with a shift in [0, d - 1] and __y is a duration count.
      template <unsigned __d, typename _Tp>
      constexpr unsigned
      __add_modulo(unsigned __x, _Tp __y)
      {
   using _Up = make_unsigned_t<_Tp>;
   // For __y >= 0, _Up(__y) has the same mathematical value as __y and
   // this function simply returns (__x + _Up(__y)) % d.  Typically, this
   // doesn't overflow since the range of _Up contains many more positive
   // values than _Tp's.  For __y < 0, _Up(__y) has a mathematical value in
   // the upper-half range of _Up so that adding a positive value to it
   // might overflow.  Moreover, most likely, _Up(__y) != __y mod d.  To
   // fix both issues we subtract from _Up(__y) an __offset >=
   // 255 + d - 1 to make room for the addition to __x and shift the modulo
   // to the correct value.
   auto const __offset = __y >= 0 ? _Up(0) : __modulo_offset<__d, _Tp>();
   return (__x + _Up(__y) - __offset) % __d;
      }

      // Similar to __add_modulo but for __x - __y.
      template <unsigned __d, typename _Tp>
      constexpr unsigned
      __sub_modulo(unsigned __x, _Tp __y)
      {
   using _Up = make_unsigned_t<_Tp>;
   auto const __offset = __y <= 0 ? _Up(0) : __modulo_offset<__d, _Tp>();
   return (__x - _Up(__y) - __offset) % __d;
      }

      inline constexpr unsigned __days_per_month[12]
   = { 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
    }

    // DAY

    class day
    {
    private:
      unsigned char _M_d;

    public:
      day() = default;

      explicit constexpr
      day(unsigned __d) noexcept
      : _M_d(__d)
      { }

      constexpr day&
      operator++() noexcept
      {
   ++_M_d;
   return *this;
      }

      constexpr day
      operator++(int) noexcept
      {
   auto __ret = *this;
   ++(*this);
   return __ret;
      }

      constexpr day&
      operator--() noexcept
      {
   --_M_d;
   return *this;
      }

      constexpr day
      operator--(int) noexcept
      {
   auto __ret = *this;
   --(*this);
   return __ret;
      }

      constexpr day&
      operator+=(const days& __d) noexcept
      {
   *this = *this + __d;
   return *this;
      }

      constexpr day&
      operator-=(const days& __d) noexcept
      {
   *this = *this - __d;
   return *this;
      }

      constexpr explicit
      operator unsigned() const noexcept
      { return _M_d; }

      constexpr bool
      ok() const noexcept
      { return 1 <= _M_d && _M_d <= 31; }

      friend constexpr bool
      operator==(const day& __x, const day& __y) noexcept
      { return unsigned{__x} == unsigned{__y}; }

      friend constexpr strong_ordering
      operator<=>(const day& __x, const day& __y) noexcept
      { return unsigned{__x} <=> unsigned{__y}; }

      friend constexpr day
      operator+(const day& __x, const days& __y) noexcept
      { return day(unsigned{__x} + __y.count()); }

      friend constexpr day
      operator+(const days& __x, const day& __y) noexcept
      { return __y + __x; }

      friend constexpr day
      operator-(const day& __x, const days& __y) noexcept
      { return __x + -__y; }

      friend constexpr days
      operator-(const day& __x, const day& __y) noexcept
      { return days{int(unsigned{__x}) - int(unsigned{__y})}; }

      friend constexpr month_day
      operator/(const month& __m, const day& __d) noexcept;

      friend constexpr month_day
      operator/(int __m, const day& __d) noexcept;

      friend constexpr month_day
      operator/(const day& __d, const month& __m) noexcept;

      friend constexpr month_day
      operator/(const day& __d, int __m) noexcept;

      friend constexpr year_month_day
      operator/(const year_month& __ym, const day& __d) noexcept;

      // TODO: Implement operator<<, to_stream, from_stream.
    };

    // MONTH

    class month
    {
    private:
      unsigned char _M_m;

    public:
      month() = default;

      explicit constexpr
      month(unsigned __m) noexcept
      : _M_m(__m)
      { }

      constexpr month&
      operator++() noexcept
      {
   *this += months{1};
   return *this;
      }

      constexpr month
      operator++(int) noexcept
      {
   auto __ret = *this;
   ++(*this);
   return __ret;
      }

      constexpr month&
      operator--() noexcept
      {
   *this -= months{1};
   return *this;
      }

      constexpr month
      operator--(int) noexcept
      {
   auto __ret = *this;
   --(*this);
   return __ret;
      }

      constexpr month&
      operator+=(const months& __m) noexcept
      {
   *this = *this + __m;
   return *this;
      }

      constexpr month&
      operator-=(const months& __m) noexcept
      {
   *this = *this - __m;
   return *this;
      }

      explicit constexpr
      operator unsigned() const noexcept
      { return _M_m; }

      constexpr bool
      ok() const noexcept
      { return 1 <= _M_m && _M_m <= 12; }

      friend constexpr bool
      operator==(const month& __x, const month& __y) noexcept
      { return unsigned{__x} == unsigned{__y}; }

      friend constexpr strong_ordering
      operator<=>(const month& __x, const month& __y) noexcept
      { return unsigned{__x} <=> unsigned{__y}; }

      friend constexpr month
      operator+(const month& __x, const months& __y) noexcept
      {
   // modulo(x + (y - 1), 12) = modulo(x + (y - 1) + 12, 12)
   //                         = modulo((x + 11) + y    , 12)
   return month{1 + __detail::__add_modulo<12>(
     unsigned{__x} + 11, __y.count())};
      }

      friend constexpr month
      operator+(const months& __x,  const month& __y) noexcept
      { return __y + __x; }

      friend constexpr month
      operator-(const month& __x, const months& __y) noexcept
      {
   // modulo(x + (-y - 1), 12) = modulo(x + (-y - 1) + 12, 12)
   //                          = modulo((x + 11) - y     , 12)
   return month{1 + __detail::__sub_modulo<12>(
     unsigned{__x} + 11, __y.count())};
      }

      friend constexpr months
      operator-(const month& __x,  const month& __y) noexcept
      {
   const auto __dm = int(unsigned(__x)) - int(unsigned(__y));
   return months{__dm < 0 ? 12 + __dm : __dm};
      }

      friend constexpr year_month
      operator/(const year& __y, const month& __m) noexcept;

      friend constexpr month_day
      operator/(const month& __m, int __d) noexcept;

      friend constexpr month_day_last
      operator/(const month& __m, last_spec) noexcept;

      friend constexpr month_day_last
      operator/(last_spec, const month& __m) noexcept;

      friend constexpr month_weekday
      operator/(const month& __m, const weekday_indexed& __wdi) noexcept;

      friend constexpr month_weekday
      operator/(const weekday_indexed& __wdi, const month& __m) noexcept;

      friend constexpr month_weekday_last
      operator/(const month& __m, const weekday_last& __wdl) noexcept;

      friend constexpr month_weekday_last
      operator/(const weekday_last& __wdl, const month& __m) noexcept;

      // TODO: Implement operator<<, to_stream, from_stream.
    };

    inline constexpr month January{1};
    inline constexpr month February{2};
    inline constexpr month March{3};
    inline constexpr month April{4};
    inline constexpr month May{5};
    inline constexpr month June{6};
    inline constexpr month July{7};
    inline constexpr month August{8};
    inline constexpr month September{9};
    inline constexpr month October{10};
    inline constexpr month November{11};
    inline constexpr month December{12};

    // YEAR

    class year
    {
    private:
      short _M_y;

    public:
      year() = default;

      explicit constexpr
      year(int __y) noexcept
      : _M_y{static_cast<short>(__y)}
      { }

      static constexpr year
      min() noexcept
      { return year{-32767}; }

      static constexpr year
      max() noexcept
      { return year{32767}; }

      constexpr year&
      operator++() noexcept
      {
   ++_M_y;
   return *this;
      }

      constexpr year
      operator++(int) noexcept
      {
   auto __ret = *this;
   ++(*this);
   return __ret;
      }

      constexpr year&
      operator--() noexcept
      {
   --_M_y;
   return *this;
      }

      constexpr year
      operator--(int) noexcept
      {
   auto __ret = *this;
   --(*this);
   return __ret;
      }

      constexpr year&
      operator+=(const years& __y) noexcept
      {
   *this = *this + __y;
   return *this;
      }

      constexpr year&
      operator-=(const years& __y) noexcept
      {
   *this = *this - __y;
   return *this;
      }

      constexpr year
      operator+() const noexcept
      { return *this; }

      constexpr year
      operator-() const noexcept
      { return year{-_M_y}; }

      constexpr bool
      is_leap() const noexcept
      {
   // Testing divisibility by 100 first gives better performance [1], i.e.,
   //     return _M_y % 100 == 0 ? _M_y % 400 == 0 : _M_y % 16 == 0;
   // Furthermore, if _M_y % 100 == 0, then _M_y % 400 == 0 is equivalent
   // to _M_y % 16 == 0, so we can simplify it to
   //     return _M_y % 100 == 0 ? _M_y % 16 == 0 : _M_y % 4 == 0.  // #1
   // Similarly, we can replace 100 with 25 (which is good since
   // _M_y % 25 == 0 requires one fewer instruction than _M_y % 100 == 0
   // [2]):
   //     return _M_y % 25 == 0 ? _M_y % 16 == 0 : _M_y % 4 == 0.  // #2
   // Indeed, first assume _M_y % 4 != 0.  Then _M_y % 16 != 0 and hence,
   // _M_y % 4 == 0 and _M_y % 16 == 0 are both false.  Therefore, #2
   // returns false as it should (regardless of _M_y % 25.) Now assume
   // _M_y % 4 == 0.  In this case, _M_y % 25 == 0 if, and only if,
   // _M_y % 100 == 0, that is, #1 and #2 are equivalent.  Finally, #2 is
   // equivalent to
   //     return (_M_y & (_M_y % 25 == 0 ? 15 : 3)) == 0.

   // References:
   // [1] https://github.com/cassioneri/calendar
   // [2] https://godbolt.org/z/55G8rn77e
   // [3] https://gcc.gnu.org/pipermail/libstdc++/2021-June/052815.html

   return (_M_y & (_M_y % 25 == 0 ? 15 : 3)) == 0;
      }

      explicit constexpr
      operator int() const noexcept
      { return _M_y; }

      constexpr bool
      ok() const noexcept
      { return min()._M_y <= _M_y && _M_y <= max()._M_y; }

      friend constexpr bool
      operator==(const year& __x, const year& __y) noexcept
      { return int{__x} == int{__y}; }

      friend constexpr strong_ordering
      operator<=>(const year& __x, const year& __y) noexcept
      { return int{__x} <=> int{__y}; }

      friend constexpr year
      operator+(const year& __x, const years& __y) noexcept
      { return year{int{__x} + static_cast<int>(__y.count())}; }

      friend constexpr year
      operator+(const years& __x, const year& __y) noexcept
      { return __y + __x; }

      friend constexpr year
      operator-(const year& __x, const years& __y) noexcept
      { return __x + -__y; }

      friend constexpr years
      operator-(const year& __x, const year& __y) noexcept
      { return years{int{__x} - int{__y}}; }

      friend constexpr year_month
      operator/(const year& __y, int __m) noexcept;

      friend constexpr year_month_day
      operator/(const year& __y, const month_day& __md) noexcept;

      friend constexpr year_month_day
      operator/(const month_day& __md, const year& __y) noexcept;

      friend constexpr year_month_day_last
      operator/(const year& __y, const month_day_last& __mdl) noexcept;

      friend constexpr year_month_day_last
      operator/(const month_day_last& __mdl, const year& __y) noexcept;

      friend constexpr year_month_weekday
      operator/(const year& __y, const month_weekday& __mwd) noexcept;

      friend constexpr year_month_weekday
      operator/(const month_weekday& __mwd, const year& __y) noexcept;

      friend constexpr year_month_weekday_last
      operator/(const year& __y, const month_weekday_last& __mwdl) noexcept;

      friend constexpr year_month_weekday_last
      operator/(const month_weekday_last& __mwdl, const year& __y) noexcept;

      // TODO: Implement operator<<, to_stream, from_stream.
    };

    // WEEKDAY

    class weekday
    {
    private:
      unsigned char _M_wd;

      static constexpr weekday
      _S_from_days(const days& __d)
      {
   return weekday{__detail::__add_modulo<7>(4, __d.count())};
      }

    public:
      weekday() = default;

      explicit constexpr
      weekday(unsigned __wd) noexcept
      : _M_wd(__wd == 7 ? 0 : __wd) // __wd % 7 ?
      { }

      constexpr
      weekday(const sys_days& __dp) noexcept
      : weekday{_S_from_days(__dp.time_since_epoch())}
      { }

      explicit constexpr
      weekday(const local_days& __dp) noexcept
      : weekday{sys_days{__dp.time_since_epoch()}}
      { }

      constexpr weekday&
      operator++() noexcept
      {
   *this += days{1};
   return *this;
      }

      constexpr weekday
      operator++(int) noexcept
      {
   auto __ret = *this;
   ++(*this);
   return __ret;
      }

      constexpr weekday&
      operator--() noexcept
      {
   *this -= days{1};
   return *this;
      }

      constexpr weekday
      operator--(int) noexcept
      {
   auto __ret = *this;
   --(*this);
   return __ret;
      }

      constexpr weekday&
      operator+=(const days& __d) noexcept
      {
   *this = *this + __d;
   return *this;
      }

      constexpr weekday&
      operator-=(const days& __d) noexcept
      {
   *this = *this - __d;
   return *this;
      }

      constexpr unsigned
      c_encoding() const noexcept
      { return _M_wd; }

      constexpr unsigned
      iso_encoding() const noexcept
      { return _M_wd == 0u ? 7u : _M_wd; }

      constexpr bool
      ok() const noexcept
      { return _M_wd <= 6; }

      constexpr weekday_indexed
      operator[](unsigned __index) const noexcept;

      constexpr weekday_last
      operator[](last_spec) const noexcept;

      friend constexpr bool
      operator==(const weekday& __x, const weekday& __y) noexcept
      { return __x._M_wd == __y._M_wd; }

      friend constexpr weekday
      operator+(const weekday& __x, const days& __y) noexcept
      {
   return weekday{__detail::__add_modulo<7>(__x._M_wd, __y.count())};
      }

      friend constexpr weekday
      operator+(const days& __x, const weekday& __y) noexcept
      { return __y + __x; }

      friend constexpr weekday
      operator-(const weekday& __x, const days& __y) noexcept
      {
   return weekday{__detail::__sub_modulo<7>(__x._M_wd, __y.count())};
      }

      friend constexpr days
      operator-(const weekday& __x, const weekday& __y) noexcept
      {
   const auto __n = __x.c_encoding() - __y.c_encoding();
   return static_cast<int>(__n) >= 0 ? days{__n} : days{__n + 7};
      }

      // TODO: operator<<, from_stream.
    };

    inline constexpr weekday Sunday{0};
    inline constexpr weekday Monday{1};
    inline constexpr weekday Tuesday{2};
    inline constexpr weekday Wednesday{3};
    inline constexpr weekday Thursday{4};
    inline constexpr weekday Friday{5};
    inline constexpr weekday Saturday{6};

    // WEEKDAY_INDEXED

    class weekday_indexed
    {
    private:
      chrono::weekday _M_wd;
      unsigned char _M_index;

    public:
      weekday_indexed() = default;

      constexpr
      weekday_indexed(const chrono::weekday& __wd, unsigned __index) noexcept
      : _M_wd(__wd), _M_index(__index)
      { }

      constexpr chrono::weekday
      weekday() const noexcept
      { return _M_wd; }

      constexpr unsigned
      index() const noexcept
      { return _M_index; };

      constexpr bool
      ok() const noexcept
      { return _M_wd.ok() && 1 <= _M_index && _M_index <= 5; }

      friend constexpr bool
      operator==(const weekday_indexed& __x, const weekday_indexed& __y) noexcept
      { return __x.weekday() == __y.weekday() && __x.index() == __y.index(); }

      friend constexpr month_weekday
      operator/(const month& __m, const weekday_indexed& __wdi) noexcept;

      friend constexpr month_weekday
      operator/(int __m, const weekday_indexed& __wdi) noexcept;

      friend constexpr month_weekday
      operator/(const weekday_indexed& __wdi, const month& __m) noexcept;

      friend constexpr month_weekday
      operator/(const weekday_indexed& __wdi, int __m) noexcept;

      friend constexpr year_month_weekday
      operator/(const year_month& __ym, const weekday_indexed& __wdi) noexcept;

      // TODO: Implement operator<<.
    };

    constexpr weekday_indexed
    weekday::operator[](unsigned __index) const noexcept
    { return {*this, __index}; }

    // WEEKDAY_LAST

    class weekday_last
    {
    private:
      chrono::weekday _M_wd;

    public:
      explicit constexpr
      weekday_last(const chrono::weekday& __wd) noexcept
      : _M_wd{__wd}
      { }

      constexpr chrono::weekday
      weekday() const noexcept
      { return _M_wd; }

      constexpr bool
      ok() const noexcept
      { return _M_wd.ok(); }

      friend constexpr bool
      operator==(const weekday_last& __x, const weekday_last& __y) noexcept
      { return __x.weekday() == __y.weekday(); }

      friend constexpr month_weekday_last
      operator/(int __m, const weekday_last& __wdl) noexcept;

      friend constexpr month_weekday_last
      operator/(const weekday_last& __wdl, int __m) noexcept;

      friend constexpr year_month_weekday_last
      operator/(const year_month& __ym, const weekday_last& __wdl) noexcept;

      // TODO: Implement operator<<.
    };

    constexpr weekday_last
    weekday::operator[](last_spec) const noexcept
    { return weekday_last{*this}; }

    // MONTH_DAY

    class month_day
    {
    private:
      chrono::month _M_m;
      chrono::day _M_d;

    public:
      month_day() = default;

      constexpr
      month_day(const chrono::month& __m, const chrono::day& __d) noexcept
      : _M_m{__m}, _M_d{__d}
      { }

      constexpr chrono::month
      month() const noexcept
      { return _M_m; }

      constexpr chrono::day
      day() const noexcept
      { return _M_d; }

      constexpr bool
      ok() const noexcept
      {
   return _M_m.ok()
     && 1u <= unsigned(_M_d)
     && unsigned(_M_d) <= __detail::__days_per_month[unsigned(_M_m) - 1];
      }

      friend constexpr bool
      operator==(const month_day& __x, const month_day& __y) noexcept
      { return __x.month() == __y.month() && __x.day() == __y.day(); }

      friend constexpr strong_ordering
      operator<=>(const month_day& __x, const month_day& __y) noexcept
   = default;

      friend constexpr month_day
      operator/(const chrono::month& __m, const chrono::day& __d) noexcept
      { return {__m, __d}; }

      friend constexpr month_day
      operator/(const chrono::month& __m, int __d) noexcept
      { return {__m, chrono::day(unsigned(__d))}; }

      friend constexpr month_day
      operator/(int __m, const chrono::day& __d) noexcept
      { return {chrono::month(unsigned(__m)), __d}; }

      friend constexpr month_day
      operator/(const chrono::day& __d, const chrono::month& __m) noexcept
      { return {__m, __d}; }

      friend constexpr month_day
      operator/(const chrono::day& __d, int __m) noexcept
      { return {chrono::month(unsigned(__m)), __d}; }

      friend constexpr year_month_day
      operator/(int __y, const month_day& __md) noexcept;

      friend constexpr year_month_day
      operator/(const month_day& __md, int __y) noexcept;

      // TODO: Implement operator<<, from_stream.
    };

    // MONTH_DAY_LAST

    class month_day_last
    {
    private:
      chrono::month _M_m;

    public:
      explicit constexpr
      month_day_last(const chrono::month& __m) noexcept
      : _M_m{__m}
      { }

      constexpr chrono::month
      month() const noexcept
      { return _M_m; }

      constexpr bool
      ok() const noexcept
      { return _M_m.ok(); }

      friend constexpr bool
      operator==(const month_day_last& __x, const month_day_last& __y) noexcept
      { return __x.month() == __y.month(); }

      friend constexpr strong_ordering
      operator<=>(const month_day_last& __x, const month_day_last& __y) noexcept
   = default;

      friend constexpr month_day_last
      operator/(const chrono::month& __m, last_spec) noexcept
      { return month_day_last{__m}; }

      friend constexpr month_day_last
      operator/(int __m, last_spec) noexcept
      { return chrono::month(unsigned(__m)) / last; }

      friend constexpr month_day_last
      operator/(last_spec, const chrono::month& __m) noexcept
      { return __m / last; }

      friend constexpr month_day_last
      operator/(last_spec, int __m) noexcept
      { return __m / last; }

      friend constexpr year_month_day_last
      operator/(int __y, const month_day_last& __mdl) noexcept;

      friend constexpr year_month_day_last
      operator/(const month_day_last& __mdl, int __y) noexcept;

      // TODO: Implement operator<<.
    };

    // MONTH_WEEKDAY

    class month_weekday
    {
    private:
      chrono::month _M_m;
      chrono::weekday_indexed _M_wdi;

    public:
      constexpr
      month_weekday(const chrono::month& __m,
               const chrono::weekday_indexed& __wdi) noexcept
      : _M_m{__m}, _M_wdi{__wdi}
      { }

      constexpr chrono::month
      month() const noexcept
      { return _M_m; }

      constexpr chrono::weekday_indexed
      weekday_indexed() const noexcept
      { return _M_wdi; }

      constexpr bool
      ok() const noexcept
      { return _M_m.ok() && _M_wdi.ok(); }

      friend constexpr bool
      operator==(const month_weekday& __x, const month_weekday& __y) noexcept
      {
   return __x.month() == __y.month()
     && __x.weekday_indexed() == __y.weekday_indexed();
      }

      friend constexpr month_weekday
      operator/(const chrono::month& __m,
           const chrono::weekday_indexed& __wdi) noexcept
      { return {__m, __wdi}; }

      friend constexpr month_weekday
      operator/(int __m, const chrono::weekday_indexed& __wdi) noexcept
      { return chrono::month(unsigned(__m)) / __wdi; }

      friend constexpr month_weekday
      operator/(const chrono::weekday_indexed& __wdi,
           const chrono::month& __m) noexcept
      { return __m / __wdi; }

      friend constexpr month_weekday
      operator/(const chrono::weekday_indexed& __wdi, int __m) noexcept
      { return __m / __wdi; }

      friend constexpr year_month_weekday
      operator/(int __y, const month_weekday& __mwd) noexcept;

      friend constexpr year_month_weekday
      operator/(const month_weekday& __mwd, int __y) noexcept;

      // TODO: Implement operator<<.
    };

    // MONTH_WEEKDAY_LAST

    class month_weekday_last
    {
    private:
      chrono::month _M_m;
      chrono::weekday_last _M_wdl;

    public:
      constexpr
      month_weekday_last(const chrono::month& __m,
                    const chrono::weekday_last& __wdl) noexcept
      :_M_m{__m}, _M_wdl{__wdl}
      { }

      constexpr chrono::month
      month() const noexcept
      { return _M_m; }

      constexpr chrono::weekday_last
      weekday_last() const noexcept
      { return _M_wdl; }

      constexpr bool
      ok() const noexcept
      { return _M_m.ok() && _M_wdl.ok(); }

      friend constexpr bool
      operator==(const month_weekday_last& __x,
            const month_weekday_last& __y) noexcept
      {
   return __x.month() == __y.month()
     && __x.weekday_last() == __y.weekday_last();
      }

      friend constexpr month_weekday_last
      operator/(const chrono::month& __m,
           const chrono::weekday_last& __wdl) noexcept
      { return {__m, __wdl}; }

      friend constexpr month_weekday_last
      operator/(int __m, const chrono::weekday_last& __wdl) noexcept
      { return chrono::month(unsigned(__m)) / __wdl; }

      friend constexpr month_weekday_last
      operator/(const chrono::weekday_last& __wdl,
           const chrono::month& __m) noexcept
      { return __m / __wdl; }

      friend constexpr month_weekday_last
      operator/(const chrono::weekday_last& __wdl, int __m) noexcept
      { return chrono::month(unsigned(__m)) / __wdl; }

      friend constexpr year_month_weekday_last
      operator/(int __y, const month_weekday_last& __mwdl) noexcept;

      friend constexpr year_month_weekday_last
      operator/(const month_weekday_last& __mwdl, int __y) noexcept;

      // TODO: Implement operator<<.
    };

    // YEAR_MONTH

    namespace __detail
    {
      // [time.cal.ym], [time.cal.ymd], etc constrain the 'months'-based
      // addition/subtraction operator overloads like so:
      //
      //   Constraints: if the argument supplied by the caller for the months
      //   parameter is convertible to years, its implicit conversion sequence
      //   to years is worse than its implicit conversion sequence to months.
      //
      // We realize this constraint by templatizing the 'months'-based
      // overloads (using a dummy defaulted template parameter), so that
      // overload resolution doesn't select the 'months'-based overload unless
      // the implicit conversion sequence to 'months' is better than that to
      // 'years'.
      using __months_years_conversion_disambiguator = void;
    }

    class year_month
    {
    private:
      chrono::year _M_y;
      chrono::month _M_m;

    public:
      year_month() = default;

      constexpr
      year_month(const chrono::year& __y, const chrono::month& __m) noexcept
      : _M_y{__y}, _M_m{__m}
      { }

      constexpr chrono::year
      year() const noexcept
      { return _M_y; }

      constexpr chrono::month
      month() const noexcept
      { return _M_m; }

      template<typename = __detail::__months_years_conversion_disambiguator>
   constexpr year_month&
   operator+=(const months& __dm) noexcept
   {
     *this = *this + __dm;
     return *this;
   }

      template<typename = __detail::__months_years_conversion_disambiguator>
   constexpr year_month&
   operator-=(const months& __dm) noexcept
   {
     *this = *this - __dm;
     return *this;
   }

      constexpr year_month&
      operator+=(const years& __dy)  noexcept
      {
   *this = *this + __dy;
   return *this;
      }

      constexpr year_month&
      operator-=(const years& __dy)  noexcept
      {
   *this = *this - __dy;
   return *this;
      }

      constexpr bool
      ok() const noexcept
      { return _M_y.ok() && _M_m.ok(); }

      friend constexpr bool
      operator==(const year_month& __x, const year_month& __y) noexcept
      { return __x.year() == __y.year() && __x.month() == __y.month(); }

      friend constexpr strong_ordering
      operator<=>(const year_month& __x, const year_month& __y) noexcept
   = default;

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month
   operator+(const year_month& __ym, const months& __dm) noexcept
   {
     // TODO: Optimize?
     auto __m = __ym.month() + __dm;
     auto __i = int(unsigned(__ym.month())) - 1 + __dm.count();
     auto __y = (__i < 0
                 ? __ym.year() + years{(__i - 11) / 12}
                 : __ym.year() + years{__i / 12});
     return __y / __m;
   }

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month
   operator+(const months& __dm, const year_month& __ym) noexcept
   { return __ym + __dm; }

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month
   operator-(const year_month& __ym, const months& __dm) noexcept
   { return __ym + -__dm; }

      friend constexpr months
      operator-(const year_month& __x, const year_month& __y) noexcept
      {
   return (__x.year() - __y.year()
           + months{static_cast<int>(unsigned{__x.month()})
                    - static_cast<int>(unsigned{__y.month()})});
      }

      friend constexpr year_month
      operator+(const year_month& __ym, const years& __dy) noexcept
      { return (__ym.year() + __dy) / __ym.month(); }

      friend constexpr year_month
      operator+(const years& __dy, const year_month& __ym) noexcept
      { return __ym + __dy; }

      friend constexpr year_month
      operator-(const year_month& __ym, const years& __dy) noexcept
      { return __ym + -__dy; }

      friend constexpr year_month
      operator/(const chrono::year& __y, const chrono::month& __m) noexcept
      { return {__y, __m}; }

      friend constexpr year_month
      operator/(const chrono::year& __y, int __m) noexcept
      { return {__y, chrono::month(unsigned(__m))}; }

      friend constexpr year_month_day
      operator/(const year_month& __ym, int __d) noexcept;

      friend constexpr year_month_day_last
      operator/(const year_month& __ym, last_spec) noexcept;

      // TODO: Implement operator<<, from_stream.
    };

    // YEAR_MONTH_DAY

    class year_month_day
    {
    private:
      chrono::year _M_y;
      chrono::month _M_m;
      chrono::day _M_d;

      static constexpr year_month_day _S_from_days(const days& __dp) noexcept;

      constexpr days _M_days_since_epoch() const noexcept;

    public:
      year_month_day() = default;

      constexpr
      year_month_day(const chrono::year& __y, const chrono::month& __m,
                const chrono::day& __d) noexcept
      : _M_y{__y}, _M_m{__m}, _M_d{__d}
      { }

      constexpr
      year_month_day(const year_month_day_last& __ymdl) noexcept;

      constexpr
      year_month_day(const sys_days& __dp) noexcept
      : year_month_day(_S_from_days(__dp.time_since_epoch()))
      { }

      explicit constexpr
      year_month_day(const local_days& __dp) noexcept
      : year_month_day(sys_days{__dp.time_since_epoch()})
      { }

      template<typename = __detail::__months_years_conversion_disambiguator>
   constexpr year_month_day&
   operator+=(const months& __m) noexcept
   {
     *this = *this + __m;
     return *this;
   }

      template<typename = __detail::__months_years_conversion_disambiguator>
   constexpr year_month_day&
   operator-=(const months& __m) noexcept
   {
     *this = *this - __m;
     return *this;
   }

      constexpr year_month_day&
      operator+=(const years& __y) noexcept
      {
   *this = *this + __y;
   return *this;
      }

      constexpr year_month_day&
      operator-=(const years& __y) noexcept
      {
   *this = *this - __y;
   return *this;
      }

      constexpr chrono::year
      year() const noexcept
      { return _M_y; }

      constexpr chrono::month
      month() const noexcept
      { return _M_m; }

      constexpr chrono::day
      day() const noexcept
      { return _M_d; }

      constexpr
      operator sys_days() const noexcept
      { return sys_days{_M_days_since_epoch()}; }

      explicit constexpr
      operator local_days() const noexcept
      { return local_days{sys_days{*this}.time_since_epoch()}; }

      constexpr bool ok() const noexcept;

      friend constexpr bool
      operator==(const year_month_day& __x, const year_month_day& __y) noexcept
      {
   return __x.year() == __y.year()
     && __x.month() == __y.month()
     && __x.day() == __y.day();
      }

      friend constexpr strong_ordering
      operator<=>(const year_month_day& __x, const year_month_day& __y) noexcept
   = default;

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month_day
   operator+(const year_month_day& __ymd, const months& __dm) noexcept
   { return (__ymd.year() / __ymd.month() + __dm) / __ymd.day(); }

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month_day
   operator+(const months& __dm, const year_month_day& __ymd) noexcept
   { return __ymd + __dm; }

      friend constexpr year_month_day
      operator+(const year_month_day& __ymd, const years& __dy) noexcept
      { return (__ymd.year() + __dy) / __ymd.month() / __ymd.day(); }

      friend constexpr year_month_day
      operator+(const years& __dy, const year_month_day& __ymd) noexcept
      { return __ymd + __dy; }

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month_day
   operator-(const year_month_day& __ymd, const months& __dm) noexcept
   { return __ymd + -__dm; }

      friend constexpr year_month_day
      operator-(const year_month_day& __ymd, const years& __dy) noexcept
      { return __ymd + -__dy; }

      friend constexpr year_month_day
      operator/(const year_month& __ym, const chrono::day& __d) noexcept
      { return {__ym.year(), __ym.month(), __d}; }

      friend constexpr year_month_day
      operator/(const year_month& __ym, int __d) noexcept
      { return __ym / chrono::day{unsigned(__d)}; }

      friend constexpr year_month_day
      operator/(const chrono::year& __y, const month_day& __md) noexcept
      { return __y / __md.month() / __md.day(); }

      friend constexpr year_month_day
      operator/(int __y, const month_day& __md) noexcept
      { return chrono::year{__y} / __md; }

      friend constexpr year_month_day
      operator/(const month_day& __md, const chrono::year& __y) noexcept
      { return __y / __md; }

      friend constexpr year_month_day
      operator/(const month_day& __md, int __y) noexcept
      { return chrono::year(__y) / __md; }

      // TODO: Implement operator<<, from_stream.
    };

    // Construct from days since 1970/01/01.
    // Proposition 6.3 of Neri and Schneider,
    // "Euclidean Affine Functions and Applications to Calendar Algorithms".
    // https://arxiv.org/abs/2102.06959
    constexpr year_month_day
    year_month_day::_S_from_days(const days& __dp) noexcept
    {
      constexpr auto __z2    = static_cast<uint32_t>(-1468000);
      constexpr auto __r2_e3 = static_cast<uint32_t>(536895458);

      const auto __r0 = static_cast<uint32_t>(__dp.count()) + __r2_e3;

      const auto __n1 = 4 * __r0 + 3;
      const auto __q1 = __n1 / 146097;
      const auto __r1 = __n1 % 146097 / 4;

      constexpr auto __p32 = static_cast<uint64_t>(1) << 32;
      const auto __n2 = 4 * __r1 + 3;
      const auto __u2 = static_cast<uint64_t>(2939745) * __n2;
      const auto __q2 = static_cast<uint32_t>(__u2 / __p32);
      const auto __r2 = static_cast<uint32_t>(__u2 % __p32) / 2939745 / 4;

      constexpr auto __p16 = static_cast<uint32_t>(1) << 16;
      const auto __n3 = 2141 * __r2 + 197913;
      const auto __q3 = __n3 / __p16;
      const auto __r3 = __n3 % __p16 / 2141;

      const auto __y0 = 100 * __q1 + __q2;
      const auto __m0 = __q3;
      const auto __d0 = __r3;

      const auto __j  = __r2 >= 306;
      const auto __y1 = __y0 + __j;
      const auto __m1 = __j ? __m0 - 12 : __m0;
      const auto __d1 = __d0 + 1;

      return year_month_day{chrono::year{static_cast<int>(__y1 + __z2)},
                       chrono::month{__m1}, chrono::day{__d1}};
    }

    // Days since 1970/01/01.
    // Proposition 6.2 of Neri and Schneider,
    // "Euclidean Affine Functions and Applications to Calendar Algorithms".
    // https://arxiv.org/abs/2102.06959
    constexpr days
    year_month_day::_M_days_since_epoch() const noexcept
    {
      auto constexpr __z2    = static_cast<uint32_t>(-1468000);
      auto constexpr __r2_e3 = static_cast<uint32_t>(536895458);

      const auto __y1 = static_cast<uint32_t>(static_cast<int>(_M_y)) - __z2;
      const auto __m1 = static_cast<uint32_t>(static_cast<unsigned>(_M_m));
      const auto __d1 = static_cast<uint32_t>(static_cast<unsigned>(_M_d));

      const auto __j  = static_cast<uint32_t>(__m1 < 3);
      const auto __y0 = __y1 - __j;
      const auto __m0 = __j ? __m1 + 12 : __m1;
      const auto __d0 = __d1 - 1;

      const auto __q1 = __y0 / 100;
      const auto __yc = 1461 * __y0 / 4 - __q1 + __q1 / 4;
      const auto __mc = (979 *__m0 - 2919) / 32;
      const auto __dc = __d0;

      return days{static_cast<int32_t>(__yc + __mc + __dc - __r2_e3)};
    }

    // YEAR_MONTH_DAY_LAST

    class year_month_day_last
    {
    private:
      chrono::year _M_y;
      chrono::month_day_last _M_mdl;

    public:
      constexpr
      year_month_day_last(const chrono::year& __y,
                     const chrono::month_day_last& __mdl) noexcept
      : _M_y{__y}, _M_mdl{__mdl}
      { }

      template<typename = __detail::__months_years_conversion_disambiguator>
   constexpr year_month_day_last&
   operator+=(const months& __m) noexcept
   {
     *this = *this + __m;
     return *this;
   }

      template<typename = __detail::__months_years_conversion_disambiguator>
   constexpr year_month_day_last&
   operator-=(const months& __m) noexcept
   {
     *this = *this - __m;
     return *this;
   }

      constexpr year_month_day_last&
      operator+=(const years& __y)  noexcept
      {
   *this = *this + __y;
   return *this;
      }

      constexpr year_month_day_last&
      operator-=(const years& __y)  noexcept
      {
   *this = *this - __y;
   return *this;
      }

      constexpr chrono::year
      year() const noexcept
      { return _M_y; }

      constexpr chrono::month
      month() const noexcept
      { return _M_mdl.month(); }

      constexpr chrono::month_day_last
      month_day_last() const noexcept
      { return _M_mdl; }

      // Return A day representing the last day of this year, month pair.
      constexpr chrono::day
      day() const noexcept
      {
   const auto __m = static_cast<unsigned>(month());

   // The result is unspecified if __m < 1 or __m > 12.  Hence, assume
   // 1 <= __m <= 12.  For __m != 2, day() == 30 or day() == 31 or, in
   // other words, day () == 30 | b, where b is in {0, 1}.

   // If __m in {1, 3, 4, 5, 6, 7}, then b is 1 if, and only if, __m is
   // odd.  Hence, b = __m & 1 = (__m ^ 0) & 1.

   // If __m in {8, 9, 10, 11, 12}, then b is 1 if, and only if, __m is
   // even.  Hence, b = (__m ^ 1) & 1.

   // Therefore, b = (__m ^ c) & 1, where c = 0, if __m < 8, or c = 1 if
   // __m >= 8, that is, c = __m >> 3.

   // Since 30 = (11110)_2 and __m <= 31 = (11111)_2, the "& 1" in b's
   // calculation is unnecessary.

   // The performance of this implementation does not depend on look-up
   // tables being on the L1 cache.
   return chrono::day{__m != 2 ? (__m ^ (__m >> 3)) | 30
     : _M_y.is_leap() ? 29 : 28};
      }

      constexpr
      operator sys_days() const noexcept
      { return sys_days{year() / month() / day()}; }

      explicit constexpr
      operator local_days() const noexcept
      { return local_days{sys_days{*this}.time_since_epoch()}; }

      constexpr bool
      ok() const noexcept
      { return _M_y.ok() && _M_mdl.ok(); }

      friend constexpr bool
      operator==(const year_month_day_last& __x,
            const year_month_day_last& __y) noexcept
      {
   return __x.year() == __y.year()
     && __x.month_day_last() == __y.month_day_last();
      }

      friend constexpr strong_ordering
      operator<=>(const year_month_day_last& __x,
             const year_month_day_last& __y) noexcept
   = default;

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month_day_last
   operator+(const year_month_day_last& __ymdl,
             const months& __dm) noexcept
   { return (__ymdl.year() / __ymdl.month() + __dm) / last; }

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month_day_last
   operator+(const months& __dm,
             const year_month_day_last& __ymdl) noexcept
   { return __ymdl + __dm; }

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month_day_last
   operator-(const year_month_day_last& __ymdl,
             const months& __dm) noexcept
   { return __ymdl + -__dm; }

      friend constexpr year_month_day_last
      operator+(const year_month_day_last& __ymdl,
           const years& __dy) noexcept
      { return {__ymdl.year() + __dy, __ymdl.month_day_last()}; }

      friend constexpr year_month_day_last
      operator+(const years& __dy,
           const year_month_day_last& __ymdl) noexcept
      { return __ymdl + __dy; }

      friend constexpr year_month_day_last
      operator-(const year_month_day_last& __ymdl,
           const years& __dy) noexcept
      { return __ymdl + -__dy; }

      friend constexpr year_month_day_last
      operator/(const year_month& __ym, last_spec) noexcept
      { return {__ym.year(), chrono::month_day_last{__ym.month()}}; }

      friend constexpr year_month_day_last
      operator/(const chrono::year& __y,
           const chrono::month_day_last& __mdl) noexcept
      { return {__y, __mdl}; }

      friend constexpr year_month_day_last
      operator/(int __y, const chrono::month_day_last& __mdl) noexcept
      { return chrono::year(__y) / __mdl; }

      friend constexpr year_month_day_last
      operator/(const chrono::month_day_last& __mdl,
           const chrono::year& __y) noexcept
      { return __y / __mdl; }

      friend constexpr year_month_day_last
      operator/(const chrono::month_day_last& __mdl, int __y) noexcept
      { return chrono::year(__y) / __mdl; }

      // TODO: Implement operator<<.
    };

    // year_month_day ctor from year_month_day_last
    constexpr
    year_month_day::year_month_day(const year_month_day_last& __ymdl) noexcept
    : _M_y{__ymdl.year()}, _M_m{__ymdl.month()}, _M_d{__ymdl.day()}
    { }

    constexpr bool
    year_month_day::ok() const noexcept
    {
      if (!_M_y.ok() || !_M_m.ok())
   return false;
      return chrono::day{1} <= _M_d && _M_d <= (_M_y / _M_m / last).day();
    }

    // YEAR_MONTH_WEEKDAY

    class year_month_weekday
    {
    private:
      chrono::year _M_y;
      chrono::month _M_m;
      chrono::weekday_indexed _M_wdi;

      static constexpr year_month_weekday
      _S_from_sys_days(const sys_days& __dp)
      {
   year_month_day __ymd{__dp};
   chrono::weekday __wd{__dp};
   auto __index = __wd[(unsigned{__ymd.day()} - 1) / 7 + 1];
   return {__ymd.year(), __ymd.month(), __index};
      }

    public:
      year_month_weekday() = default;

      constexpr
      year_month_weekday(const chrono::year& __y, const chrono::month& __m,
                    const chrono::weekday_indexed& __wdi) noexcept
      : _M_y{__y}, _M_m{__m}, _M_wdi{__wdi}
      { }

      constexpr
      year_month_weekday(const sys_days& __dp) noexcept
      : year_month_weekday{_S_from_sys_days(__dp)}
      { }

      explicit constexpr
      year_month_weekday(const local_days& __dp) noexcept
      : year_month_weekday{sys_days{__dp.time_since_epoch()}}
      { }

      template<typename = __detail::__months_years_conversion_disambiguator>
   constexpr year_month_weekday&
   operator+=(const months& __m) noexcept
   {
     *this = *this + __m;
     return *this;
   }

      template<typename = __detail::__months_years_conversion_disambiguator>
   constexpr year_month_weekday&
   operator-=(const months& __m) noexcept
   {
     *this = *this - __m;
     return *this;
   }

      constexpr year_month_weekday&
      operator+=(const years& __y) noexcept
      {
   *this = *this + __y;
   return *this;
      }

      constexpr year_month_weekday&
      operator-=(const years& __y) noexcept
      {
   *this = *this - __y;
   return *this;
      }

      constexpr chrono::year
      year() const noexcept
      { return _M_y; }

      constexpr chrono::month
      month() const noexcept
      { return _M_m; }

      constexpr chrono::weekday
      weekday() const noexcept
      { return _M_wdi.weekday(); }

      constexpr unsigned
      index() const noexcept
      { return _M_wdi.index(); }

      constexpr chrono::weekday_indexed
      weekday_indexed() const noexcept
      { return _M_wdi; }

      constexpr
      operator sys_days() const noexcept
      {
   auto __d = sys_days{year() / month() / 1};
   return __d + (weekday() - chrono::weekday(__d)
                 + days{(static_cast<int>(index())-1)*7});
      }

      explicit constexpr
      operator local_days() const noexcept
      { return local_days{sys_days{*this}.time_since_epoch()}; }

      constexpr bool
      ok() const noexcept
      {
   if (!_M_y.ok() || !_M_m.ok() || !_M_wdi.ok())
     return false;
   if (_M_wdi.index() <= 4)
     return true;
   days __d = (_M_wdi.weekday()
               - chrono::weekday{sys_days{_M_y / _M_m / 1}}
               + days((_M_wdi.index()-1)*7 + 1));
   __glibcxx_assert(__d.count() >= 1);
   return __d.count() <= unsigned{(_M_y / _M_m / last).day()};
      }

      friend constexpr bool
      operator==(const year_month_weekday& __x,
            const year_month_weekday& __y) noexcept
      {
   return __x.year() == __y.year()
     && __x.month() == __y.month()
     && __x.weekday_indexed() == __y.weekday_indexed();
      }

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month_weekday
   operator+(const year_month_weekday& __ymwd, const months& __dm) noexcept
   {
     return ((__ymwd.year() / __ymwd.month() + __dm)
             / __ymwd.weekday_indexed());
   }

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month_weekday
   operator+(const months& __dm, const year_month_weekday& __ymwd) noexcept
   { return __ymwd + __dm; }

      friend constexpr year_month_weekday
      operator+(const year_month_weekday& __ymwd, const years& __dy) noexcept
      { return {__ymwd.year() + __dy, __ymwd.month(), __ymwd.weekday_indexed()}; }

      friend constexpr year_month_weekday
      operator+(const years& __dy, const year_month_weekday& __ymwd) noexcept
      { return __ymwd + __dy; }

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month_weekday
   operator-(const year_month_weekday& __ymwd, const months& __dm) noexcept
   { return __ymwd + -__dm; }

      friend constexpr year_month_weekday
      operator-(const year_month_weekday& __ymwd, const years& __dy) noexcept
      { return __ymwd + -__dy; }

      friend constexpr year_month_weekday
      operator/(const year_month& __ym,
           const chrono::weekday_indexed& __wdi) noexcept
      { return {__ym.year(), __ym.month(), __wdi}; }

      friend constexpr year_month_weekday
      operator/(const chrono::year& __y, const month_weekday& __mwd) noexcept
      { return {__y, __mwd.month(), __mwd.weekday_indexed()}; }

      friend constexpr year_month_weekday
      operator/(int __y, const month_weekday& __mwd) noexcept
      { return chrono::year(__y) / __mwd; }

      friend constexpr year_month_weekday
      operator/(const month_weekday& __mwd, const chrono::year& __y) noexcept
      { return __y / __mwd; }

      friend constexpr year_month_weekday
      operator/(const month_weekday& __mwd, int __y) noexcept
      { return chrono::year(__y) / __mwd; }

      // TODO: Implement operator<<.
    };

    // YEAR_MONTH_WEEKDAY_LAST

    class year_month_weekday_last
    {
    private:
      chrono::year _M_y;
      chrono::month _M_m;
      chrono::weekday_last _M_wdl;

    public:
      constexpr
      year_month_weekday_last(const chrono::year& __y, const chrono::month& __m,
                         const chrono::weekday_last& __wdl) noexcept
      : _M_y{__y}, _M_m{__m}, _M_wdl{__wdl}
      { }

      template<typename = __detail::__months_years_conversion_disambiguator>
   constexpr year_month_weekday_last&
   operator+=(const months& __m) noexcept
   {
     *this = *this + __m;
     return *this;
   }

      template<typename = __detail::__months_years_conversion_disambiguator>
   constexpr year_month_weekday_last&
   operator-=(const months& __m) noexcept
   {
     *this = *this - __m;
     return *this;
   }

      constexpr year_month_weekday_last&
      operator+=(const years& __y)  noexcept
      {
   *this = *this + __y;
   return *this;
      }

      constexpr year_month_weekday_last&
      operator-=(const years& __y)  noexcept
      {
   *this = *this - __y;
   return *this;
      }

      constexpr chrono::year
      year() const noexcept
      { return _M_y; }

      constexpr chrono::month
      month() const noexcept
      { return _M_m; }

      constexpr chrono::weekday
      weekday() const noexcept
      { return _M_wdl.weekday(); }

      constexpr chrono::weekday_last
      weekday_last() const noexcept
      { return _M_wdl; }

      constexpr
      operator sys_days() const noexcept
      {
   const auto __d = sys_days{_M_y / _M_m / last};
   return sys_days{(__d - (chrono::weekday{__d}
                           - _M_wdl.weekday())).time_since_epoch()};
      }

      explicit constexpr
      operator local_days() const noexcept
      { return local_days{sys_days{*this}.time_since_epoch()}; }

      constexpr bool
      ok() const noexcept
      { return _M_y.ok() && _M_m.ok() && _M_wdl.ok(); }

      friend constexpr bool
      operator==(const year_month_weekday_last& __x,
            const year_month_weekday_last& __y) noexcept
      {
   return __x.year() == __y.year()
     && __x.month() == __y.month()
     && __x.weekday_last() == __y.weekday_last();
      }

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month_weekday_last
   operator+(const year_month_weekday_last& __ymwdl,
             const months& __dm) noexcept
   {
     return ((__ymwdl.year() / __ymwdl.month() + __dm)
             / __ymwdl.weekday_last());
   }

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month_weekday_last
   operator+(const months& __dm,
             const year_month_weekday_last& __ymwdl) noexcept
   { return __ymwdl + __dm; }

      friend constexpr year_month_weekday_last
      operator+(const year_month_weekday_last& __ymwdl,
           const years& __dy) noexcept
      { return {__ymwdl.year() + __dy, __ymwdl.month(), __ymwdl.weekday_last()}; }

      friend constexpr year_month_weekday_last
      operator+(const years& __dy,
           const year_month_weekday_last& __ymwdl) noexcept
      { return __ymwdl + __dy; }

      template<typename = __detail::__months_years_conversion_disambiguator>
   friend constexpr year_month_weekday_last
   operator-(const year_month_weekday_last& __ymwdl,
             const months& __dm) noexcept
   { return __ymwdl + -__dm; }

      friend constexpr year_month_weekday_last
      operator-(const year_month_weekday_last& __ymwdl,
           const years& __dy) noexcept
      { return __ymwdl + -__dy; }

      friend constexpr year_month_weekday_last
      operator/(const year_month& __ym,
           const chrono::weekday_last& __wdl) noexcept
      { return {__ym.year(), __ym.month(), __wdl}; }

      friend constexpr year_month_weekday_last
      operator/(const chrono::year& __y,
           const chrono::month_weekday_last& __mwdl) noexcept
      { return {__y, __mwdl.month(), __mwdl.weekday_last()}; }

      friend constexpr year_month_weekday_last
      operator/(int __y, const chrono::month_weekday_last& __mwdl) noexcept
      { return chrono::year(__y) / __mwdl; }

      friend constexpr year_month_weekday_last
      operator/(const chrono::month_weekday_last& __mwdl,
           const chrono::year& __y) noexcept
      { return __y / __mwdl; }

      friend constexpr year_month_weekday_last
      operator/(const chrono::month_weekday_last& __mwdl, int __y) noexcept
      { return chrono::year(__y) / __mwdl; }

      // TODO: Implement operator<<.
    };

    // HH_MM_SS

    namespace __detail
    {
      consteval long long
      __pow10(unsigned __n)
      {
   long long __r = 1;
   while (__n-- > 0)
     __r *= 10;
   return __r;
      }
    }

    template<typename _Duration>
      class hh_mm_ss
      {
      private:
   static constexpr int
   _S_fractional_width()
   {
     int __multiplicity_2 = 0;
     int __multiplicity_5 = 0;
     auto __den = _Duration::period::den;
     while ((__den % 2) == 0)
       {
         ++__multiplicity_2;
         __den /= 2;
       }
     while ((__den % 5) == 0)
       {
         ++__multiplicity_5;
         __den /= 5;
       }
     if (__den != 1)
       return 6;

     int __width = (__multiplicity_2 > __multiplicity_5
                    ? __multiplicity_2 : __multiplicity_5);
     if (__width > 18)
       __width = 18;
     return __width;
   }

   constexpr
   hh_mm_ss(_Duration __d, bool __is_neg)
   : _M_is_neg(__is_neg),
     _M_h (duration_cast<chrono::hours>(__d)),
     _M_m (duration_cast<chrono::minutes>(__d - hours())),
     _M_s (duration_cast<chrono::seconds>(__d - hours() - minutes()))
   {
     auto __ss = __d - hours() - minutes() - seconds();
     if constexpr (treat_as_floating_point_v<typename precision::rep>)
       _M_ss = __ss;
     else
       _M_ss = duration_cast<precision>(__ss);
   }

   static constexpr _Duration
   _S_abs(_Duration __d)
   {
     if constexpr (numeric_limits<typename _Duration::rep>::is_signed)
       return chrono::abs(__d);
     else
       return __d;
   }

      public:
   static constexpr unsigned fractional_width = {_S_fractional_width()};

   using precision
     = duration<common_type_t<typename _Duration::rep,
                              chrono::seconds::rep>,
                ratio<1, __detail::__pow10(fractional_width)>>;

   constexpr
   hh_mm_ss() noexcept
   : hh_mm_ss{_Duration::zero()}
   { }

   constexpr explicit
   hh_mm_ss(_Duration __d)
   : hh_mm_ss(_S_abs(__d), __d < _Duration::zero())
   { }

   constexpr bool
   is_negative() const noexcept
   { return _M_is_neg; }

   constexpr chrono::hours
   hours() const noexcept
   { return _M_h; }

   constexpr chrono::minutes
   minutes() const noexcept
   { return _M_m; }

   constexpr chrono::seconds
   seconds() const noexcept
   { return _M_s; }

   constexpr precision
   subseconds() const noexcept
   { return _M_ss; }

   constexpr explicit
   operator precision() const noexcept
   { return to_duration(); }

   constexpr precision
   to_duration() const noexcept
   {
     if (_M_is_neg)
       return -(_M_h + _M_m + _M_s + _M_ss);
     else
       return _M_h + _M_m + _M_s + _M_ss;
   }

   // TODO: Implement operator<<.

      private:
   bool _M_is_neg;
   chrono::hours _M_h;
   chrono::minutes _M_m;
   chrono::seconds _M_s;
   precision _M_ss;
      };

    // 12/24 HOURS FUNCTIONS

    constexpr bool
    is_am(const hours& __h) noexcept
    { return 0h <= __h && __h <= 11h; }

    constexpr bool
    is_pm(const hours& __h) noexcept
    { return 12h <= __h && __h <= 23h; }

    constexpr hours
    make12(const hours& __h) noexcept
    {
      if (__h == 0h)
   return 12h;
      else if (__h > 12h)
   return __h - 12h;
      return __h;
    }

    constexpr hours
    make24(const hours& __h, bool __is_pm) noexcept
    {
      if (!__is_pm)
   {
     if (__h == 12h)
       return 0h;
     else
       return __h;
   }
      else
   {
     if (__h == 12h)
       return __h;
     else
       return __h + 12h;
   }
    }
    /// @} group chrono
#endif // C++20
  } // namespace chrono

#if __cplusplus >= 202002L
  inline namespace literals
  {
  inline namespace chrono_literals
  {
    /// @addtogroup chrono
    /// @{
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wliteral-suffix"
    /// Literal suffix for creating chrono::day objects.
    /// @since C++20
    constexpr chrono::day
    operator""d(unsigned long long __d) noexcept
    { return chrono::day{static_cast<unsigned>(__d)}; }

    /// Literal suffix for creating chrono::year objects.
    /// @since C++20
    constexpr chrono::year
    operator""y(unsigned long long __y) noexcept
    { return chrono::year{static_cast<int>(__y)}; }
#pragma GCC diagnostic pop
    /// @}
  } // inline namespace chrono_literals
  } // inline namespace literals

  namespace chrono
  {
    /// @addtogroup chrono
    /// @{

    /// @cond undocumented
    namespace __detail
    {
      template<typename _Period>
   const char*
   __units_suffix_misc(char* __buf, size_t __n) noexcept
   {
     namespace __tc = std::__detail;
     char* __p = __buf;
     __p[0] = '[';
     unsigned __nlen = __tc::__to_chars_len((uintmax_t)_Period::num);
     __tc::__to_chars_10_impl(__p + 1, __nlen, (uintmax_t)_Period::num);
     __p += 1 + __nlen;
     if constexpr (_Period::den != 1)
       {
         __p[0] = '/';
         unsigned __dlen = __tc::__to_chars_len((uintmax_t)_Period::den);
         __tc::__to_chars_10_impl(__p + 1, __dlen, (uintmax_t)_Period::den);
         __p += 1 + __dlen;
       }
     __p[0] = ']';
     __p[1] = 's';
     __p[2] = '\0';
     return __buf;
   }

      template<typename _Period, typename _CharT>
   auto
   __units_suffix(char* __buf, size_t __n) noexcept
   {
#define _GLIBCXX_UNITS_SUFFIX(period, suffix) \
   if constexpr (is_same_v<_Period, period>)       \
     {                                             \
       if constexpr (is_same_v<_CharT, wchar_t>)   \
         return L##suffix;                         \
       else                                        \
         return suffix;                            \
     }                                             \
   else

     _GLIBCXX_UNITS_SUFFIX(atto, "as")
     _GLIBCXX_UNITS_SUFFIX(femto, "fs")
     _GLIBCXX_UNITS_SUFFIX(pico, "ps")
     _GLIBCXX_UNITS_SUFFIX(nano, "ns")
     _GLIBCXX_UNITS_SUFFIX(micro, "\u00b5s")
     _GLIBCXX_UNITS_SUFFIX(milli, "ms")
     _GLIBCXX_UNITS_SUFFIX(centi, "cs")
     _GLIBCXX_UNITS_SUFFIX(deci, "ds")
     _GLIBCXX_UNITS_SUFFIX(ratio<1>, "s")
     _GLIBCXX_UNITS_SUFFIX(deca, "das")
     _GLIBCXX_UNITS_SUFFIX(hecto, "hs")
     _GLIBCXX_UNITS_SUFFIX(kilo, "ks")
     _GLIBCXX_UNITS_SUFFIX(mega, "Ms")
     _GLIBCXX_UNITS_SUFFIX(giga, "Gs")
     _GLIBCXX_UNITS_SUFFIX(tera, "Ts")
     _GLIBCXX_UNITS_SUFFIX(tera, "Ts")
     _GLIBCXX_UNITS_SUFFIX(peta, "Ps")
     _GLIBCXX_UNITS_SUFFIX(exa, "Es")
     _GLIBCXX_UNITS_SUFFIX(ratio<60>, "min")
     _GLIBCXX_UNITS_SUFFIX(ratio<3600>, "h")
     _GLIBCXX_UNITS_SUFFIX(ratio<86400>, "d")
#undef _GLIBCXX_UNITS_SUFFIX
     return __detail::__units_suffix_misc<_Period>(__buf, __n);
   }
    } // namespace __detail
    /// @endcond

    template<typename _CharT, typename _Traits,
        typename _Rep, typename _Period>
      inline basic_ostream<_CharT, _Traits>&
      operator<<(std::basic_ostream<_CharT, _Traits>& __os,
           const duration<_Rep, _Period>& __d)
      {
   using period = typename _Period::type;
   char __buf[sizeof("[/]s") + 2 * numeric_limits<intmax_t>::digits10];
   std::basic_ostringstream<_CharT, _Traits> __s;
   __s.flags(__os.flags());
   __s.imbue(__os.getloc());
   __s.precision(__os.precision());
   __s << __d.count();
   __s << __detail::__units_suffix<period, _CharT>(__buf, sizeof(__buf));
   __os << std::move(__s).str();
   return __os;
      }

    // TODO: from_stream for duration

    /// @} group chrono
  } // namespace chrono
#endif // C++20

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif // C++11

#endif //_GLIBCXX_CHRONO