Na}{

Server IP: 172.31.39.10
Your IP: 172.69.130.206
Web Server: Apache/2.4.52 (Ubuntu)
System: Linux ip-172-31-39-10 6.8.0-1029-aws #31~22.04.1-Ubuntu SMP Thu Apr 24 21:16:18 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
User: www-data
PHP Version: 7.2.34-54+ubuntu22.04.1+deb.sury.org+1
Disable Function: pcntl_alarm, pcntl_fork, pcntl_waitpid, pcntl_wait, pcntl_wifexited, pcntl_wifstopped, pcntl_wifsignaled, pcntl_wifcontinued, pcntl_wexitstatus, pcntl_wtermsig, pcntl_wstopsig, pcntl_signal, pcntl_signal_get_handler, pcntl_signal_dispatch, pcntl_get_last_error, pcntl_strerror, pcntl_sigprocmask, pcntl_sigwaitinfo, pcntl_sigtimedwait, pcntl_exec, pcntl_getpriority, pcntl_setpriority, pcntl_async_signals, [more...]
MySQL: OFF
cURL: ON
WGET: ON
Perl: ON
Python: OFF
Sudo: ON
Pkexec: ON
Command Bosku:

Path: ~//usr/include/c++/11/
File Content: `chrono`

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

// Copyright (C) 2008-2021 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 <ratio>
#include <type_traits>
#include <limits>
#include <ctime>
#include <bits/parse_numbers.h> // for literals support.
#if __cplusplus > 201703L
# include <concepts>
# include <compare>
#endif

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

#if __cplusplus >= 201703L
  namespace filesystem { struct __file_clock; };
#endif

  /**
   * @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
  {
    /// @addtogroup chrono
    /// @{

    /// `chrono::duration` represents a distance between two points in time
    template<typename _Rep, typename _Period = ratio<1>>
      struct duration;

    /// `chrono::time_point` represents a point in time as measured by a clock
    template<typename _Clock, typename _Dur = typename _Clock::duration>
      struct time_point;
    /// @}
  }

  /// @addtogroup chrono
  /// @{

  // 20.11.4.3 specialization of common_type (for duration, sfinae-friendly)

  /// @cond undocumented

  template<typename _CT, typename _Period1, typename _Period2, typename = void>
    struct __duration_common_type
    { };

  template<typename _CT, typename _Period1, typename _Period2>
    struct __duration_common_type<_CT, _Period1, _Period2,
				  __void_t<typename _CT::type>>
    {
    private:
      using __gcd_num = __static_gcd<_Period1::num, _Period2::num>;
      using __gcd_den = __static_gcd<_Period1::den, _Period2::den>;
      using __cr = typename _CT::type;
      using __r = ratio<__gcd_num::value,
			(_Period1::den / __gcd_den::value) * _Period2::den>;

    public:
      using type = chrono::duration<__cr, typename __r::type>;
    };

  /// @endcond

  /// @{
  /// @relates chrono::duration

  /// Specialization of common_type for chrono::duration types.
  template<typename _Rep1, typename _Period1, typename _Rep2, typename _Period2>
    struct common_type<chrono::duration<_Rep1, _Period1>,
		       chrono::duration<_Rep2, _Period2>>
    : __duration_common_type<common_type<_Rep1, _Rep2>,
			     typename _Period1::type,
			     typename _Period2::type>
    { };

  /// Specialization of common_type for two identical chrono::duration types.
  template<typename _Rep, typename _Period>
    struct common_type<chrono::duration<_Rep, _Period>,
		       chrono::duration<_Rep, _Period>>
    {
      using type = chrono::duration<typename common_type<_Rep>::type,
				    typename _Period::type>;
    };

  /// Specialization of common_type for one chrono::duration type.
  template<typename _Rep, typename _Period>
    struct common_type<chrono::duration<_Rep, _Period>>
    {
      using type = chrono::duration<typename common_type<_Rep>::type,
				    typename _Period::type>;
    };
  /// @}

  // 20.11.4.3 specialization of common_type (for time_point, sfinae-friendly)

  /// @cond undocumented

  template<typename _CT, typename _Clock, typename = void>
    struct __timepoint_common_type
    { };

  template<typename _CT, typename _Clock>
    struct __timepoint_common_type<_CT, _Clock, __void_t<typename _CT::type>>
    {
      using type = chrono::time_point<_Clock, typename _CT::type>;
    };

  /// @endcond

  /// @{
  /// @relates chrono::time_point

  /// Specialization of common_type for chrono::time_point types.
  template<typename _Clock, typename _Duration1, typename _Duration2>
    struct common_type<chrono::time_point<_Clock, _Duration1>,
		       chrono::time_point<_Clock, _Duration2>>
    : __timepoint_common_type<common_type<_Duration1, _Duration2>, _Clock>
    { };

  /// Specialization of common_type for two identical chrono::time_point types.
  template<typename _Clock, typename _Duration>
    struct common_type<chrono::time_point<_Clock, _Duration>,
		       chrono::time_point<_Clock, _Duration>>
    { using type = chrono::time_point<_Clock, _Duration>; };

  /// Specialization of common_type for one chrono::time_point type.
  template<typename _Clock, typename _Duration>
    struct common_type<chrono::time_point<_Clock, _Duration>>
    { using type = chrono::time_point<_Clock, _Duration>; };
  /// @}

  /// @} group chrono

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

    /// @cond undocumented

    // Primary template for duration_cast impl.
    template<typename _ToDur, typename _CF, typename _CR,
	     bool _NumIsOne = false, bool _DenIsOne = false>
      struct __duration_cast_impl
      {
	template<typename _Rep, typename _Period>
	  static constexpr _ToDur
	  __cast(const duration<_Rep, _Period>& __d)
	  {
	    typedef typename _ToDur::rep			__to_rep;
	    return _ToDur(static_cast<__to_rep>(static_cast<_CR>(__d.count())
	      * static_cast<_CR>(_CF::num)
	      / static_cast<_CR>(_CF::den)));
	  }
      };

    template<typename _ToDur, typename _CF, typename _CR>
      struct __duration_cast_impl<_ToDur, _CF, _CR, true, true>
      {
	template<typename _Rep, typename _Period>
	  static constexpr _ToDur
	  __cast(const duration<_Rep, _Period>& __d)
	  {
	    typedef typename _ToDur::rep			__to_rep;
	    return _ToDur(static_cast<__to_rep>(__d.count()));
	  }
      };

    template<typename _ToDur, typename _CF, typename _CR>
      struct __duration_cast_impl<_ToDur, _CF, _CR, true, false>
      {
	template<typename _Rep, typename _Period>
	  static constexpr _ToDur
	  __cast(const duration<_Rep, _Period>& __d)
	  {
	    typedef typename _ToDur::rep			__to_rep;
	    return _ToDur(static_cast<__to_rep>(
	      static_cast<_CR>(__d.count()) / static_cast<_CR>(_CF::den)));
	  }
      };

    template<typename _ToDur, typename _CF, typename _CR>
      struct __duration_cast_impl<_ToDur, _CF, _CR, false, true>
      {
	template<typename _Rep, typename _Period>
	  static constexpr _ToDur
	  __cast(const duration<_Rep, _Period>& __d)
	  {
	    typedef typename _ToDur::rep			__to_rep;
	    return _ToDur(static_cast<__to_rep>(
	      static_cast<_CR>(__d.count()) * static_cast<_CR>(_CF::num)));
	  }
      };

    template<typename _Tp>
      struct __is_duration
      : std::false_type
      { };

    template<typename _Rep, typename _Period>
      struct __is_duration<duration<_Rep, _Period>>
      : std::true_type
      { };

    template<typename _Tp>
      using __enable_if_is_duration
	= typename enable_if<__is_duration<_Tp>::value, _Tp>::type;

    template<typename _Tp>
      using __disable_if_is_duration
	= typename enable_if<!__is_duration<_Tp>::value, _Tp>::type;

    /// @endcond

    /// duration_cast
    template<typename _ToDur, typename _Rep, typename _Period>
      constexpr __enable_if_is_duration<_ToDur>
      duration_cast(const duration<_Rep, _Period>& __d)
      {
	typedef typename _ToDur::period				__to_period;
	typedef typename _ToDur::rep				__to_rep;
	typedef ratio_divide<_Period, __to_period> 		__cf;
	typedef typename common_type<__to_rep, _Rep, intmax_t>::type
	  							__cr;
	typedef  __duration_cast_impl<_ToDur, __cf, __cr,
				      __cf::num == 1, __cf::den == 1> __dc;
	return __dc::__cast(__d);
      }

    /// treat_as_floating_point
    template<typename _Rep>
      struct treat_as_floating_point
      : is_floating_point<_Rep>
      { };

#if __cplusplus > 201402L
    template <typename _Rep>
      inline constexpr bool treat_as_floating_point_v =
        treat_as_floating_point<_Rep>::value;
#endif // C++17

#if __cplusplus > 201703L
    template<typename _Tp>
      struct is_clock;

    template<typename _Tp>
      inline constexpr bool is_clock_v = is_clock<_Tp>::value;

#if __cpp_lib_concepts
    template<typename _Tp>
      struct is_clock : false_type
      { };

    template<typename _Tp>
      requires requires {
	typename _Tp::rep;
	typename _Tp::period;
	typename _Tp::duration;
	typename _Tp::time_point::clock;
	typename _Tp::time_point::duration;
	{ &_Tp::is_steady } -> same_as<const bool*>;
	{ _Tp::now() } -> same_as<typename _Tp::time_point>;
	requires same_as<typename _Tp::duration,
			 duration<typename _Tp::rep, typename _Tp::period>>;
	requires same_as<typename _Tp::time_point::duration,
			 typename _Tp::duration>;
      }
      struct is_clock<_Tp> : true_type
      { };
#else
    template<typename _Tp, typename = void>
      struct __is_clock_impl : false_type
      { };

    template<typename _Tp>
      struct __is_clock_impl<_Tp,
			     void_t<typename _Tp::rep, typename _Tp::period,
				    typename _Tp::duration,
				    typename _Tp::time_point::duration,
				    decltype(_Tp::is_steady),
				    decltype(_Tp::now())>>
      : __and_<is_same<typename _Tp::duration,
		       duration<typename _Tp::rep, typename _Tp::period>>,
	       is_same<typename _Tp::time_point::duration,
		       typename _Tp::duration>,
	       is_same<decltype(&_Tp::is_steady), const bool*>,
	       is_same<decltype(_Tp::now()), typename _Tp::time_point>>::type
      { };

    template<typename _Tp>
      struct is_clock : __is_clock_impl<_Tp>::type
      { };
#endif
#endif // C++20

#if __cplusplus >= 201703L
# define __cpp_lib_chrono 201611

    template<typename _ToDur, typename _Rep, typename _Period>
      constexpr __enable_if_is_duration<_ToDur>
      floor(const duration<_Rep, _Period>& __d)
      {
	auto __to = chrono::duration_cast<_ToDur>(__d);
	if (__to > __d)
	  return __to - _ToDur{1};
	return __to;
      }

    template<typename _ToDur, typename _Rep, typename _Period>
      constexpr __enable_if_is_duration<_ToDur>
      ceil(const duration<_Rep, _Period>& __d)
      {
	auto __to = chrono::duration_cast<_ToDur>(__d);
	if (__to < __d)
	  return __to + _ToDur{1};
	return __to;
      }

    template <typename _ToDur, typename _Rep, typename _Period>
      constexpr enable_if_t<
	__and_<__is_duration<_ToDur>,
	       __not_<treat_as_floating_point<typename _ToDur::rep>>>::value,
	_ToDur>
      round(const duration<_Rep, _Period>& __d)
      {
	_ToDur __t0 = chrono::floor<_ToDur>(__d);
	_ToDur __t1 = __t0 + _ToDur{1};
	auto __diff0 = __d - __t0;
	auto __diff1 = __t1 - __d;
	if (__diff0 == __diff1)
	{
	    if (__t0.count() & 1)
		return __t1;
	    return __t0;
	}
	else if (__diff0 < __diff1)
	    return __t0;
	return __t1;
      }

    template<typename _Rep, typename _Period>
      constexpr
      enable_if_t<numeric_limits<_Rep>::is_signed, duration<_Rep, _Period>>
      abs(duration<_Rep, _Period> __d)
      {
	if (__d >= __d.zero())
	  return __d;
	return -__d;
      }

    // Make chrono::ceil<D> also usable as chrono::__detail::ceil<D>.
    namespace __detail { using chrono::ceil; }

#else // ! C++17

    // We want to use ceil even when compiling for earlier standards versions.
    // C++11 only allows a single statement in a constexpr function, so we
    // need to move the comparison into a separate function, __ceil_impl.
    namespace __detail
    {
      template<typename _Tp, typename _Up>
	constexpr _Tp
	__ceil_impl(const _Tp& __t, const _Up& __u)
	{
	  return (__t < __u) ? (__t + _Tp{1}) : __t;
	}

      // C++11-friendly version of std::chrono::ceil<D> for internal use.
      template<typename _ToDur, typename _Rep, typename _Period>
	constexpr _ToDur
	ceil(const duration<_Rep, _Period>& __d)
	{
	  return __detail::__ceil_impl(chrono::duration_cast<_ToDur>(__d), __d);
	}
    }
#endif // C++17

    /// duration_values
    template<typename _Rep>
      struct duration_values
      {
	static constexpr _Rep
	zero() noexcept
	{ return _Rep(0); }

	static constexpr _Rep
	max() noexcept
	{ return numeric_limits<_Rep>::max(); }

	static constexpr _Rep
	min() noexcept
	{ return numeric_limits<_Rep>::lowest(); }
      };

    /// @cond undocumented

    template<typename _Tp>
      struct __is_ratio
      : std::false_type
      { };

    template<intmax_t _Num, intmax_t _Den>
      struct __is_ratio<ratio<_Num, _Den>>
      : std::true_type
      { };

    /// @endcond

    template<typename _Rep, typename _Period>
      struct duration
      {
      private:
	template<typename _Rep2>
	  using __is_float = treat_as_floating_point<_Rep2>;

	static constexpr intmax_t
	_S_gcd(intmax_t __m, intmax_t __n) noexcept
	{
	  // Duration only allows positive periods so we don't need to
	  // handle negative values here (unlike __static_gcd and std::gcd).
#if __cplusplus >= 201402L
	  do
	    {
	      intmax_t __rem = __m % __n;
	      __m = __n;
	      __n = __rem;
	    }
	  while (__n != 0);
	  return __m;
#else
	  // C++11 doesn't allow loops in constexpr functions, but this
	  // recursive version can be more expensive to evaluate.
	  return (__n == 0) ? __m : _S_gcd(__n, __m % __n);
#endif
	}

	// _GLIBCXX_RESOLVE_LIB_DEFECTS
	// 2094. overflow shouldn't participate in overload resolution
	// 3090. What is [2094] intended to mean?
	// This only produces a valid type if no overflow occurs.
	template<typename _R1, typename _R2,
		 intmax_t __gcd1 = _S_gcd(_R1::num, _R2::num),
		 intmax_t __gcd2 = _S_gcd(_R1::den, _R2::den)>
	  using __divide = ratio<(_R1::num / __gcd1) * (_R2::den / __gcd2),
				 (_R1::den / __gcd2) * (_R2::num / __gcd1)>;

	// _Period2 is an exact multiple of _Period
	template<typename _Period2>
	  using __is_harmonic
	    = __bool_constant<__divide<_Period2, _Period>::den == 1>;

      public:

	using rep = _Rep;
	using period = typename _Period::type;

	static_assert(!__is_duration<_Rep>::value, "rep cannot be a duration");
	static_assert(__is_ratio<_Period>::value,
		      "period must be a specialization of ratio");
	static_assert(_Period::num > 0, "period must be positive");

	// 20.11.5.1 construction / copy / destroy
	constexpr duration() = default;

	duration(const duration&) = default;

	// _GLIBCXX_RESOLVE_LIB_DEFECTS
	// 3050. Conversion specification problem in chrono::duration
	template<typename _Rep2, typename = _Require<
		 is_convertible<const _Rep2&, rep>,
		 __or_<__is_float<rep>, __not_<__is_float<_Rep2>>>>>
	  constexpr explicit duration(const _Rep2& __rep)
	  : __r(static_cast<rep>(__rep)) { }

	template<typename _Rep2, typename _Period2, typename = _Require<
		 is_convertible<const _Rep2&, rep>,
		 __or_<__is_float<rep>,
		       __and_<__is_harmonic<_Period2>,
			      __not_<__is_float<_Rep2>>>>>>
	  constexpr duration(const duration<_Rep2, _Period2>& __d)
	  : __r(duration_cast<duration>(__d).count()) { }

	~duration() = default;
	duration& operator=(const duration&) = default;

	// 20.11.5.2 observer
	constexpr rep
	count() const
	{ return __r; }

	// 20.11.5.3 arithmetic

	constexpr duration<typename common_type<rep>::type, period>
	operator+() const
	{ return duration<typename common_type<rep>::type, period>(__r); }

	constexpr duration<typename common_type<rep>::type, period>
	operator-() const
	{ return duration<typename common_type<rep>::type, period>(-__r); }

	_GLIBCXX17_CONSTEXPR duration&
	operator++()
	{
	  ++__r;
	  return *this;
	}

	_GLIBCXX17_CONSTEXPR duration
	operator++(int)
	{ return duration(__r++); }

	_GLIBCXX17_CONSTEXPR duration&
	operator--()
	{
	  --__r;
	  return *this;
	}

	_GLIBCXX17_CONSTEXPR duration
	operator--(int)
	{ return duration(__r--); }

	_GLIBCXX17_CONSTEXPR duration&
	operator+=(const duration& __d)
	{
	  __r += __d.count();
	  return *this;
	}

	_GLIBCXX17_CONSTEXPR duration&
	operator-=(const duration& __d)
	{
	  __r -= __d.count();
	  return *this;
	}

	_GLIBCXX17_CONSTEXPR duration&
	operator*=(const rep& __rhs)
	{
	  __r *= __rhs;
	  return *this;
	}

	_GLIBCXX17_CONSTEXPR duration&
	operator/=(const rep& __rhs)
	{
	  __r /= __rhs;
	  return *this;
	}

	// DR 934.
	template<typename _Rep2 = rep>
	  _GLIBCXX17_CONSTEXPR
	  typename enable_if<!treat_as_floating_point<_Rep2>::value,
			     duration&>::type
	  operator%=(const rep& __rhs)
	  {
	    __r %= __rhs;
	    return *this;
	  }

	template<typename _Rep2 = rep>
	  _GLIBCXX17_CONSTEXPR
	  typename enable_if<!treat_as_floating_point<_Rep2>::value,
			     duration&>::type
	  operator%=(const duration& __d)
	  {
	    __r %= __d.count();
	    return *this;
	  }

	// 20.11.5.4 special values
	static constexpr duration
	zero() noexcept
	{ return duration(duration_values<rep>::zero()); }

	static constexpr duration
	min() noexcept
	{ return duration(duration_values<rep>::min()); }

	static constexpr duration
	max() noexcept
	{ return duration(duration_values<rep>::max()); }

      private:
	rep __r;
      };

    /// @{
    /// @relates std::chrono::duration

    /// The sum of two durations.
    template<typename _Rep1, typename _Period1,
	     typename _Rep2, typename _Period2>
      constexpr typename common_type<duration<_Rep1, _Period1>,
				     duration<_Rep2, _Period2>>::type
      operator+(const duration<_Rep1, _Period1>& __lhs,
		const duration<_Rep2, _Period2>& __rhs)
      {
	typedef duration<_Rep1, _Period1>			__dur1;
	typedef duration<_Rep2, _Period2>			__dur2;
	typedef typename common_type<__dur1,__dur2>::type	__cd;
	return __cd(__cd(__lhs).count() + __cd(__rhs).count());
      }

    /// The difference between two durations.
    template<typename _Rep1, typename _Period1,
	     typename _Rep2, typename _Period2>
      constexpr typename common_type<duration<_Rep1, _Period1>,
				     duration<_Rep2, _Period2>>::type
      operator-(const duration<_Rep1, _Period1>& __lhs,
		const duration<_Rep2, _Period2>& __rhs)
      {
	typedef duration<_Rep1, _Period1>			__dur1;
	typedef duration<_Rep2, _Period2>			__dur2;
	typedef typename common_type<__dur1,__dur2>::type	__cd;
	return __cd(__cd(__lhs).count() - __cd(__rhs).count());
      }

    /// @}

    /// @cond undocumented

    // SFINAE helper to obtain common_type<_Rep1, _Rep2> only if _Rep2
    // is implicitly convertible to it.
    // _GLIBCXX_RESOLVE_LIB_DEFECTS
    // 3050. Conversion specification problem in chrono::duration constructor
    template<typename _Rep1, typename _Rep2,
	     typename _CRep = typename common_type<_Rep1, _Rep2>::type>
      using __common_rep_t = typename
	enable_if<is_convertible<const _Rep2&, _CRep>::value, _CRep>::type;

    /// @endcond

    /** @{
     * Arithmetic operators for chrono::duration
     * @relates std::chrono::duration
     */

    template<typename _Rep1, typename _Period, typename _Rep2>
      constexpr duration<__common_rep_t<_Rep1, _Rep2>, _Period>
      operator*(const duration<_Rep1, _Period>& __d, const _Rep2& __s)
      {
	typedef duration<typename common_type<_Rep1, _Rep2>::type, _Period>
	  __cd;
	return __cd(__cd(__d).count() * __s);
      }

    template<typename _Rep1, typename _Rep2, typename _Period>
      constexpr duration<__common_rep_t<_Rep2, _Rep1>, _Period>
      operator*(const _Rep1& __s, const duration<_Rep2, _Period>& __d)
      { return __d * __s; }

    template<typename _Rep1, typename _Period, typename _Rep2>
      constexpr
      duration<__common_rep_t<_Rep1, __disable_if_is_duration<_Rep2>>, _Period>
      operator/(const duration<_Rep1, _Period>& __d, const _Rep2& __s)
      {
	typedef duration<typename common_type<_Rep1, _Rep2>::type, _Period>
	  __cd;
	return __cd(__cd(__d).count() / __s);
      }

    template<typename _Rep1, typename _Period1,
	     typename _Rep2, typename _Period2>
      constexpr typename common_type<_Rep1, _Rep2>::type
      operator/(const duration<_Rep1, _Period1>& __lhs,
		const duration<_Rep2, _Period2>& __rhs)
      {
	typedef duration<_Rep1, _Period1>			__dur1;
	typedef duration<_Rep2, _Period2>			__dur2;
	typedef typename common_type<__dur1,__dur2>::type	__cd;
	return __cd(__lhs).count() / __cd(__rhs).count();
      }

    // DR 934.
    template<typename _Rep1, typename _Period, typename _Rep2>
      constexpr
      duration<__common_rep_t<_Rep1, __disable_if_is_duration<_Rep2>>, _Period>
      operator%(const duration<_Rep1, _Period>& __d, const _Rep2& __s)
      {
	typedef duration<typename common_type<_Rep1, _Rep2>::type, _Period>
	  __cd;
	return __cd(__cd(__d).count() % __s);
      }

    template<typename _Rep1, typename _Period1,
	     typename _Rep2, typename _Period2>
      constexpr typename common_type<duration<_Rep1, _Period1>,
				     duration<_Rep2, _Period2>>::type
      operator%(const duration<_Rep1, _Period1>& __lhs,
		const duration<_Rep2, _Period2>& __rhs)
      {
	typedef duration<_Rep1, _Period1>			__dur1;
	typedef duration<_Rep2, _Period2>			__dur2;
	typedef typename common_type<__dur1,__dur2>::type	__cd;
	return __cd(__cd(__lhs).count() % __cd(__rhs).count());
      }
    /// @}

    // comparisons

    /** @{
     * Comparisons for chrono::duration
     * @relates std::chrono::duration
     */

    template<typename _Rep1, typename _Period1,
	     typename _Rep2, typename _Period2>
      constexpr bool
      operator==(const duration<_Rep1, _Period1>& __lhs,
		 const duration<_Rep2, _Period2>& __rhs)
      {
	typedef duration<_Rep1, _Period1>			__dur1;
	typedef duration<_Rep2, _Period2>			__dur2;
	typedef typename common_type<__dur1,__dur2>::type	__ct;
	return __ct(__lhs).count() == __ct(__rhs).count();
      }

    template<typename _Rep1, typename _Period1,
	     typename _Rep2, typename _Period2>
      constexpr bool
      operator<(const duration<_Rep1, _Period1>& __lhs,
		const duration<_Rep2, _Period2>& __rhs)
      {
	typedef duration<_Rep1, _Period1>			__dur1;
	typedef duration<_Rep2, _Period2>			__dur2;
	typedef typename common_type<__dur1,__dur2>::type	__ct;
	return __ct(__lhs).count() < __ct(__rhs).count();
      }

#if __cpp_lib_three_way_comparison
    template<typename _Rep1, typename _Period1,
	     typename _Rep2, typename _Period2>
      requires three_way_comparable<common_type_t<_Rep1, _Rep2>>
      constexpr auto
      operator<=>(const duration<_Rep1, _Period1>& __lhs,
		  const duration<_Rep2, _Period2>& __rhs)
      {
	using __ct = common_type_t<duration<_Rep1, _Period1>,
				   duration<_Rep2, _Period2>>;
	return __ct(__lhs).count() <=> __ct(__rhs).count();
      }
#else
    template<typename _Rep1, typename _Period1,
	     typename _Rep2, typename _Period2>
      constexpr bool
      operator!=(const duration<_Rep1, _Period1>& __lhs,
		 const duration<_Rep2, _Period2>& __rhs)
      { return !(__lhs == __rhs); }
#endif

    template<typename _Rep1, typename _Period1,
	     typename _Rep2, typename _Period2>
      constexpr bool
      operator<=(const duration<_Rep1, _Period1>& __lhs,
		 const duration<_Rep2, _Period2>& __rhs)
      { return !(__rhs < __lhs); }

    template<typename _Rep1, typename _Period1,
	     typename _Rep2, typename _Period2>
      constexpr bool
      operator>(const duration<_Rep1, _Period1>& __lhs,
		const duration<_Rep2, _Period2>& __rhs)
      { return __rhs < __lhs; }

    template<typename _Rep1, typename _Period1,
	     typename _Rep2, typename _Period2>
      constexpr bool
      operator>=(const duration<_Rep1, _Period1>& __lhs,
		 const duration<_Rep2, _Period2>& __rhs)
      { return !(__lhs < __rhs); }

    /// @}

    /// @cond undocumented
#ifdef _GLIBCXX_USE_C99_STDINT_TR1
# define _GLIBCXX_CHRONO_INT64_T int64_t
#elif defined __INT64_TYPE__
# define _GLIBCXX_CHRONO_INT64_T __INT64_TYPE__
#else
    static_assert(std::numeric_limits<unsigned long long>::digits >= 64,
	"Representation type for nanoseconds must have at least 64 bits");
# define _GLIBCXX_CHRONO_INT64_T long long
#endif
    /// @endcond

    /// nanoseconds
    using nanoseconds	= duration<_GLIBCXX_CHRONO_INT64_T, nano>;

    /// microseconds
    using microseconds	= duration<_GLIBCXX_CHRONO_INT64_T, micro>;

    /// milliseconds
    using milliseconds	= duration<_GLIBCXX_CHRONO_INT64_T, milli>;

    /// seconds
    using seconds	= duration<_GLIBCXX_CHRONO_INT64_T>;

    /// minutes
    using minutes	= duration<_GLIBCXX_CHRONO_INT64_T, ratio< 60>>;

    /// hours
    using hours		= duration<_GLIBCXX_CHRONO_INT64_T, ratio<3600>>;

#if __cplusplus > 201703L
    /// days
    using days		= duration<_GLIBCXX_CHRONO_INT64_T, ratio<86400>>;

    /// weeks
    using weeks		= duration<_GLIBCXX_CHRONO_INT64_T, ratio<604800>>;

    /// years
    using years		= duration<_GLIBCXX_CHRONO_INT64_T, ratio<31556952>>;

    /// months
    using months	= duration<_GLIBCXX_CHRONO_INT64_T, ratio<2629746>>;
#endif // C++20

#undef _GLIBCXX_CHRONO_INT64_T

    template<typename _Clock, typename _Dur>
      struct time_point
      {
	static_assert(__is_duration<_Dur>::value,
	    "duration must be a specialization of std::chrono::duration");

	typedef _Clock						clock;
	typedef _Dur						duration;
	typedef typename duration::rep				rep;
	typedef typename duration::period			period;

	constexpr time_point() : __d(duration::zero())
	{ }

	constexpr explicit time_point(const duration& __dur)
	: __d(__dur)
	{ }

	// conversions
	template<typename _Dur2,
		 typename = _Require<is_convertible<_Dur2, _Dur>>>
	  constexpr time_point(const time_point<clock, _Dur2>& __t)
	  : __d(__t.time_since_epoch())
	  { }

	// observer
	constexpr duration
	time_since_epoch() const
	{ return __d; }

#if __cplusplus > 201703L
	constexpr time_point&
	operator++()
	{
	  ++__d;
	  return *this;
	}

	constexpr time_point
	operator++(int)
	{ return time_point{__d++}; }

	constexpr time_point&
	operator--()
	{
	  --__d;
	  return *this;
	}

	constexpr time_point
	operator--(int)
	{ return time_point{__d--}; }
#endif

	// arithmetic
	_GLIBCXX17_CONSTEXPR time_point&
	operator+=(const duration& __dur)
	{
	  __d += __dur;
	  return *this;
	}

	_GLIBCXX17_CONSTEXPR time_point&
	operator-=(const duration& __dur)
	{
	  __d -= __dur;
	  return *this;
	}

	// special values
	static constexpr time_point
	min() noexcept
	{ return time_point(duration::min()); }

	static constexpr time_point
	max() noexcept
	{ return time_point(duration::max()); }

      private:
	duration __d;
      };

    /// time_point_cast
    template<typename _ToDur, typename _Clock, typename _Dur>
      constexpr typename enable_if<__is_duration<_ToDur>::value,
				   time_point<_Clock, _ToDur>>::type
      time_point_cast(const time_point<_Clock, _Dur>& __t)
      {
	typedef time_point<_Clock, _ToDur>			__time_point;
	return __time_point(duration_cast<_ToDur>(__t.time_since_epoch()));
      }

#if __cplusplus > 201402L
    template<typename _ToDur, typename _Clock, typename _Dur>
      constexpr
      enable_if_t<__is_duration<_ToDur>::value, time_point<_Clock, _ToDur>>
      floor(const time_point<_Clock, _Dur>& __tp)
      {
	return time_point<_Clock, _ToDur>{
	    chrono::floor<_ToDur>(__tp.time_since_epoch())};
      }

    template<typename _ToDur, typename _Clock, typename _Dur>
      constexpr
      enable_if_t<__is_duration<_ToDur>::value, time_point<_Clock, _ToDur>>
      ceil(const time_point<_Clock, _Dur>& __tp)
      {
	return time_point<_Clock, _ToDur>{
	    chrono::ceil<_ToDur>(__tp.time_since_epoch())};
      }

    template<typename _ToDur, typename _Clock, typename _Dur>
      constexpr enable_if_t<
	__and_<__is_duration<_ToDur>,
	       __not_<treat_as_floating_point<typename _ToDur::rep>>>::value,
	time_point<_Clock, _ToDur>>
      round(const time_point<_Clock, _Dur>& __tp)
      {
	return time_point<_Clock, _ToDur>{
	    chrono::round<_ToDur>(__tp.time_since_epoch())};
      }
#endif // C++17

    /// @{
    /// @relates time_point

    /// Adjust a time point forwards by the given duration.
    template<typename _Clock, typename _Dur1,
	     typename _Rep2, typename _Period2>
      constexpr time_point<_Clock,
	typename common_type<_Dur1, duration<_Rep2, _Period2>>::type>
      operator+(const time_point<_Clock, _Dur1>& __lhs,
		const duration<_Rep2, _Period2>& __rhs)
      {
	typedef duration<_Rep2, _Period2>			__dur2;
	typedef typename common_type<_Dur1,__dur2>::type	__ct;
	typedef time_point<_Clock, __ct>			__time_point;
	return __time_point(__lhs.time_since_epoch() + __rhs);
      }

    /// Adjust a time point forwards by the given duration.
    template<typename _Rep1, typename _Period1,
	     typename _Clock, typename _Dur2>
      constexpr time_point<_Clock,
	typename common_type<duration<_Rep1, _Period1>, _Dur2>::type>
      operator+(const duration<_Rep1, _Period1>& __lhs,
		const time_point<_Clock, _Dur2>& __rhs)
      {
	typedef duration<_Rep1, _Period1>			__dur1;
	typedef typename common_type<__dur1,_Dur2>::type	__ct;
	typedef time_point<_Clock, __ct>			__time_point;
	return __time_point(__rhs.time_since_epoch() + __lhs);
      }

    /// Adjust a time point backwards by the given duration.
    template<typename _Clock, typename _Dur1,
	     typename _Rep2, typename _Period2>
      constexpr time_point<_Clock,
	typename common_type<_Dur1, duration<_Rep2, _Period2>>::type>
      operator-(const time_point<_Clock, _Dur1>& __lhs,
		const duration<_Rep2, _Period2>& __rhs)
      {
	typedef duration<_Rep2, _Period2>			__dur2;
	typedef typename common_type<_Dur1,__dur2>::type	__ct;
	typedef time_point<_Clock, __ct>			__time_point;
	return __time_point(__lhs.time_since_epoch() -__rhs);
      }

    /// The difference between two time points (as a duration)
    template<typename _Clock, typename _Dur1, typename _Dur2>
      constexpr typename common_type<_Dur1, _Dur2>::type
      operator-(const time_point<_Clock, _Dur1>& __lhs,
		const time_point<_Clock, _Dur2>& __rhs)
      { return __lhs.time_since_epoch() - __rhs.time_since_epoch(); }
    /// @}

    /** @{
     * Comparisons for time_point
     * @relates chrono::time_point
     */

    template<typename _Clock, typename _Dur1, typename _Dur2>
      constexpr bool
      operator==(const time_point<_Clock, _Dur1>& __lhs,
		 const time_point<_Clock, _Dur2>& __rhs)
      { return __lhs.time_since_epoch() == __rhs.time_since_epoch(); }

#if __cpp_lib_three_way_comparison
    template<typename _Clock, typename _Dur1,
	     three_way_comparable_with<_Dur1> _Dur2>
      constexpr auto
      operator<=>(const time_point<_Clock, _Dur1>& __lhs,
		  const time_point<_Clock, _Dur2>& __rhs)
      { return __lhs.time_since_epoch() <=> __rhs.time_since_epoch(); }
#else
    template<typename _Clock, typename _Dur1, typename _Dur2>
      constexpr bool
      operator!=(const time_point<_Clock, _Dur1>& __lhs,
		 const time_point<_Clock, _Dur2>& __rhs)
      { return !(__lhs == __rhs); }
#endif

    template<typename _Clock, typename _Dur1, typename _Dur2>
      constexpr bool
      operator<(const time_point<_Clock, _Dur1>& __lhs,
		const time_point<_Clock, _Dur2>& __rhs)
      { return  __lhs.time_since_epoch() < __rhs.time_since_epoch(); }

    template<typename _Clock, typename _Dur1, typename _Dur2>
      constexpr bool
      operator<=(const time_point<_Clock, _Dur1>& __lhs,
		 const time_point<_Clock, _Dur2>& __rhs)
      { return !(__rhs < __lhs); }

    template<typename _Clock, typename _Dur1, typename _Dur2>
      constexpr bool
      operator>(const time_point<_Clock, _Dur1>& __lhs,
		const time_point<_Clock, _Dur2>& __rhs)
      { return __rhs < __lhs; }

    template<typename _Clock, typename _Dur1, typename _Dur2>
      constexpr bool
      operator>=(const time_point<_Clock, _Dur1>& __lhs,
		 const time_point<_Clock, _Dur2>& __rhs)
      { return !(__lhs < __rhs); }

    /// @}

    // Clocks.

    // Why nanosecond resolution as the default?
    // Why have std::system_clock always count in the highest
    // resolution (ie nanoseconds), even if on some OSes the low 3
    // or 9 decimal digits will be always zero? This allows later
    // implementations to change the system_clock::now()
    // implementation any time to provide better resolution without
    // changing function signature or units.

    // To support the (forward) evolution of the library's defined
    // clocks, wrap inside inline namespace so that the current
    // defintions of system_clock, steady_clock, and
    // high_resolution_clock types are uniquely mangled. This way, new
    // code can use the latests clocks, while the library can contain
    // compatibility definitions for previous versions.  At some
    // point, when these clocks settle down, the inlined namespaces
    // can be removed.  XXX GLIBCXX_ABI Deprecated
    inline namespace _V2 {

    /**
     *  @brief System clock.
     *
     *  Time returned represents wall time from the system-wide clock.
     *  @ingroup chrono
    */
    struct system_clock
    {
      typedef chrono::nanoseconds				duration;
      typedef duration::rep					rep;
      typedef duration::period					period;
      typedef chrono::time_point<system_clock, duration> 	time_point;

      static_assert(system_clock::duration::min()
		    < system_clock::duration::zero(),
		    "a clock's minimum duration cannot be less than its epoch");

      static constexpr bool is_steady = false;

      static time_point
      now() noexcept;

      // Map to C API
      static std::time_t
      to_time_t(const time_point& __t) noexcept
      {
	return std::time_t(duration_cast<chrono::seconds>
			   (__t.time_since_epoch()).count());
      }

      static time_point
      from_time_t(std::time_t __t) noexcept
      {
	typedef chrono::time_point<system_clock, seconds>	__from;
	return time_point_cast<system_clock::duration>
	       (__from(chrono::seconds(__t)));
      }
    };


    /**
     *  @brief Monotonic clock
     *
     *  Time returned has the property of only increasing at a uniform rate.
     *  @ingroup chrono
    */
    struct steady_clock
    {
      typedef chrono::nanoseconds				duration;
      typedef duration::rep					rep;
      typedef duration::period					period;
      typedef chrono::time_point<steady_clock, duration>	time_point;

      static constexpr bool is_steady = true;

      static time_point
      now() noexcept;
    };


    /**
     *  @brief Highest-resolution clock
     *
     *  This is the clock "with the shortest tick period." Alias to
     *  std::system_clock until higher-than-nanosecond definitions
     *  become feasible.
     *  @ingroup chrono
    */
    using high_resolution_clock = system_clock;

    } // end inline namespace _V2

#if __cplusplus > 201703L
    template<typename _Duration>
      using sys_time = time_point<system_clock, _Duration>;
    using sys_seconds = sys_time<seconds>;
    using sys_days = sys_time<days>;

    using file_clock = ::std::filesystem::__file_clock;

    template<typename _Duration>
      using file_time = time_point<file_clock, _Duration>;

    template<> struct is_clock<system_clock> : true_type { };
    template<> struct is_clock<steady_clock> : true_type { };
    template<> struct is_clock<file_clock> : true_type { };

    template<> inline constexpr bool is_clock_v<system_clock> = true;
    template<> inline constexpr bool is_clock_v<steady_clock> = true;
    template<> inline constexpr bool is_clock_v<file_clock> = true;

    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
    {
      // Compute the remainder of the Euclidean division of __n divided by __d.
      // Euclidean division truncates toward negative infinity and always
      // produces a remainder in the range of [0,__d-1] (whereas standard
      // division truncates toward zero and yields a nonpositive remainder
      // for negative __n).
      constexpr unsigned
      __modulo(long long __n, unsigned __d)
      {
	if (__n >= 0)
	  return __n % __d;
	else
	  return (__d + (__n % __d)) % __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
      {
	auto __n = static_cast<long long>(unsigned{__x}) + (__y.count() - 1);
	return month{__detail::__modulo(__n, 12) + 1};
      }

      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
      { return __x + -__y; }

      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, that is,
	// return (_M_y % 100 != 0 || _M_y % 400 == 0) && _M_y % 4 == 0;

	// It gets even faster if _M_y is in [-536870800, 536870999]
	// (which is the case here) and _M_y % 100 is replaced by
	// __is_multiple_of_100 below.

	// References:
	// [1] https://github.com/cassioneri/calendar
	// [2] https://accu.org/journals/overload/28/155/overload155.pdf#page=16

	constexpr uint32_t __multiplier   = 42949673;
	constexpr uint32_t __bound        = 42949669;
	constexpr uint32_t __max_dividend = 1073741799;
	constexpr uint32_t __offset       = __max_dividend / 2 / 100 * 100;
	const bool __is_multiple_of_100
	  = __multiplier * (_M_y + __offset) < __bound;
	return (!__is_multiple_of_100 || _M_y % 400 == 0) && _M_y % 4 == 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)
      {
	auto __n = __d.count();
	return weekday(__n >= -4 ? (__n + 4) % 7 : (__n + 5) % 7 + 6);
      }

    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
      {
	auto __n = static_cast<long long>(__x._M_wd) + __y.count();
	return weekday{__detail::__modulo(__n, 7)};
      }

      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 __x + -__y; }

      friend constexpr days
      operator-(const weekday& __x, const weekday& __y) noexcept
      {
	auto __n = static_cast<long long>(__x._M_wd) - __y._M_wd;
	return days{__detail::__modulo(__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());

	// Excluding February, the last day of month __m is either 30 or 31 or,
	// in another words, it is 30 + b = 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.

	// The above mathematically justifies this implementation whose
	// performance does not depend on look-up tables being on the L1 cache.
	return chrono::day{__m != 2 ? ((__m ^ (__m >> 3)) & 1) | 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;
      };
#endif // C++20

    /// @} group chrono
  } // namespace chrono

#if __cplusplus > 201103L

#define __cpp_lib_chrono_udls 201304

  inline namespace literals
  {
  /** ISO C++ 2014  namespace for suffixes for duration literals.
   *
   * These suffixes can be used to create `chrono::duration` values with
   * tick periods of hours, minutes, seconds, milliseconds, microseconds
   * or nanoseconds. For example, `std::chrono::seconds(5)` can be written
   * as `5s` after making the suffix visible in the current scope.
   * The suffixes can be made visible by a using-directive or
   * using-declaration such as:
   *  - `using namespace std::chrono_literals;`
   *  - `using namespace std::literals;`
   *  - `using namespace std::chrono;`
   *  - `using namespace std;`
   *  - `using std::chrono_literals::operator""s;`
   *
   * The result of these suffixes on an integer literal is one of the
   * standard typedefs such as `std::chrono::hours`.
   * The result on a floating-point literal is a duration type with the
   * specified tick period and an unspecified floating-point representation,
   * for example `1.5e2ms` might be equivalent to
   * `chrono::duration<long double, chrono::milli>(1.5e2)`.
   *
   * @ingroup chrono
   */
  inline namespace chrono_literals
  {
    /// @addtogroup chrono
    /// @{

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wliteral-suffix"
    /// @cond undocumented
    template<typename _Dur, char... _Digits>
      constexpr _Dur __check_overflow()
      {
	using _Val = __parse_int::_Parse_int<_Digits...>;
	constexpr typename _Dur::rep __repval = _Val::value;
	static_assert(__repval >= 0 && __repval == _Val::value,
		      "literal value cannot be represented by duration type");
	return _Dur(__repval);
      }
    /// @endcond

    /// Literal suffix for durations representing non-integer hours
    constexpr chrono::duration<long double, ratio<3600,1>>
    operator""h(long double __hours)
    { return chrono::duration<long double, ratio<3600,1>>{__hours}; }

    /// Literal suffix for durations of type `std::chrono::hours`
    template <char... _Digits>
      constexpr chrono::hours
      operator""h()
      { return __check_overflow<chrono::hours, _Digits...>(); }

    /// Literal suffix for durations representing non-integer minutes
    constexpr chrono::duration<long double, ratio<60,1>>
    operator""min(long double __mins)
    { return chrono::duration<long double, ratio<60,1>>{__mins}; }

    /// Literal suffix for durations of type `std::chrono::minutes`
    template <char... _Digits>
      constexpr chrono::minutes
      operator""min()
      { return __check_overflow<chrono::minutes, _Digits...>(); }

    /// Literal suffix for durations representing non-integer seconds
    constexpr chrono::duration<long double>
    operator""s(long double __secs)
    { return chrono::duration<long double>{__secs}; }

    /// Literal suffix for durations of type `std::chrono::seconds`
    template <char... _Digits>
      constexpr chrono::seconds
      operator""s()
      { return __check_overflow<chrono::seconds, _Digits...>(); }

    /// Literal suffix for durations representing non-integer milliseconds
    constexpr chrono::duration<long double, milli>
    operator""ms(long double __msecs)
    { return chrono::duration<long double, milli>{__msecs}; }

    /// Literal suffix for durations of type `std::chrono::milliseconds`
    template <char... _Digits>
      constexpr chrono::milliseconds
      operator""ms()
      { return __check_overflow<chrono::milliseconds, _Digits...>(); }

    /// Literal suffix for durations representing non-integer microseconds
    constexpr chrono::duration<long double, micro>
    operator""us(long double __usecs)
    { return chrono::duration<long double, micro>{__usecs}; }

    /// Literal suffix for durations of type `std::chrono::microseconds`
    template <char... _Digits>
      constexpr chrono::microseconds
      operator""us()
      { return __check_overflow<chrono::microseconds, _Digits...>(); }

    /// Literal suffix for durations representing non-integer nanoseconds
    constexpr chrono::duration<long double, nano>
    operator""ns(long double __nsecs)
    { return chrono::duration<long double, nano>{__nsecs}; }

    /// Literal suffix for durations of type `std::chrono::nanoseconds`
    template <char... _Digits>
      constexpr chrono::nanoseconds
      operator""ns()
      { return __check_overflow<chrono::nanoseconds, _Digits...>(); }

#if __cplusplus > 201703L
    constexpr chrono::day
    operator""d(unsigned long long __d) noexcept
    { return chrono::day{static_cast<unsigned>(__d)}; }

    constexpr chrono::year
    operator""y(unsigned long long __y) noexcept
    { return chrono::year{static_cast<int>(__y)}; }
#endif // C++20

#pragma GCC diagnostic pop
    /// @}
  } // inline namespace chrono_literals
  } // inline namespace literals

  namespace chrono
  {
    using namespace literals::chrono_literals;
  } // namespace chrono

#if __cplusplus > 201703L
  namespace chrono
  {
    /// @addtogroup chrono
    /// @{

    // 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
  } // namespace chrono
#endif

#if __cplusplus >= 201703L
  namespace filesystem
  {
    struct __file_clock
    {
      using duration                  = chrono::nanoseconds;
      using rep                       = duration::rep;
      using period                    = duration::period;
      using time_point                = chrono::time_point<__file_clock>;
      static constexpr bool is_steady = false;

      static time_point
      now() noexcept
      { return _S_from_sys(chrono::system_clock::now()); }

#if __cplusplus > 201703L
      template<typename _Dur>
	static
	chrono::file_time<_Dur>
	from_sys(const chrono::sys_time<_Dur>& __t) noexcept
	{ return _S_from_sys(__t); }

      // For internal use only
      template<typename _Dur>
	static
	chrono::sys_time<_Dur>
	to_sys(const chrono::file_time<_Dur>& __t) noexcept
	{ return _S_to_sys(__t); }
#endif // C++20

    private:
      using __sys_clock = chrono::system_clock;

      // This clock's (unspecified) epoch is 2174-01-01 00:00:00 UTC.
      // A signed 64-bit duration with nanosecond resolution gives roughly
      // +/- 292 years, which covers the 1901-2446 date range for ext4.
      static constexpr chrono::seconds _S_epoch_diff{6437664000};

    protected:
      // For internal use only
      template<typename _Dur>
	static
	chrono::time_point<__file_clock, _Dur>
	_S_from_sys(const chrono::time_point<__sys_clock, _Dur>& __t) noexcept
	{
	  using __file_time = chrono::time_point<__file_clock, _Dur>;
	  return __file_time{__t.time_since_epoch()} - _S_epoch_diff;
	}

      // For internal use only
      template<typename _Dur>
	static
	chrono::time_point<__sys_clock, _Dur>
	_S_to_sys(const chrono::time_point<__file_clock, _Dur>& __t) noexcept
	{
	  using __sys_time = chrono::time_point<__sys_clock, _Dur>;
	  return __sys_time{__t.time_since_epoch()} + _S_epoch_diff;
	}
    };
  } // namespace filesystem
#endif // C++17
#endif // C++14

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif // C++11

#endif //_GLIBCXX_CHRONO
Edit Rename Chmod Delete
FILE FOLDER
Name	Size	Permission
backward	---	0755
bits	---	0755
debug	---	0755
decimal	---	0755
experimental	---	0755
ext	---	0755
parallel	---	0755
pstl	---	0755
tr1	---	0755
tr2	---	0755
algorithm	3045 bytes	0644
any	18758 bytes	0644
array	13820 bytes	0644
atomic	48800 bytes	0644
barrier	8026 bytes	0644
bit	12187 bytes	0644
bitset	45995 bytes	0644
cassert	1648 bytes	0644
ccomplex	1335 bytes	0644
cctype	2409 bytes	0644
cerrno	1770 bytes	0644
cfenv	2051 bytes	0644
cfloat	1889 bytes	0644
charconv	19761 bytes	0644
chrono	97212 bytes	0644
cinttypes	2157 bytes	0644
ciso646	1464 bytes	0644
climits	1913 bytes	0644
clocale	1905 bytes	0644
cmath	49382 bytes	0644
codecvt	5275 bytes	0644
compare	28271 bytes	0644
complex	56703 bytes	0644
complex.h	1596 bytes	0644
concepts	12230 bytes	0644
condition_variable	12780 bytes	0644
coroutine	9156 bytes	0644
csetjmp	1949 bytes	0644
csignal	1855 bytes	0644
cstdalign	1407 bytes	0644
cstdarg	1868 bytes	0644
cstdbool	1401 bytes	0644
cstddef	6690 bytes	0644
cstdint	2335 bytes	0644
cstdio	4439 bytes	0644
cstdlib	6325 bytes	0644
cstring	3156 bytes	0644
ctgmath	1360 bytes	0644
ctime	2298 bytes	0644
cuchar	2210 bytes	0644
cwchar	6542 bytes	0644
cwctype	2793 bytes	0644
cxxabi.h	22280 bytes	0644
deque	3973 bytes	0644
exception	5017 bytes	0644
execution	1803 bytes	0644
fenv.h	2020 bytes	0644
filesystem	1645 bytes	0644
forward_list	2690 bytes	0644
fstream	40680 bytes	0644
functional	40200 bytes	0644
future	52278 bytes	0644
initializer_list	3038 bytes	0644
iomanip	16547 bytes	0644
ios	1601 bytes	0644
iosfwd	7513 bytes	0644
iostream	2697 bytes	0644
istream	34098 bytes	0644
iterator	2751 bytes	0644
latch	2732 bytes	0644
limits	71674 bytes	0644
list	3657 bytes	0644
locale	1488 bytes	0644
map	3929 bytes	0644
math.h	4573 bytes	0644
memory	4513 bytes	0644
memory_resource	21113 bytes	0644
mutex	24223 bytes	0644
new	8349 bytes	0644
numbers	6244 bytes	0644
numeric	26110 bytes	0644
optional	40170 bytes	0644
ostream	25976 bytes	0644
queue	2467 bytes	0644
random	1692 bytes	0644
ranges	107201 bytes	0644
ratio	20108 bytes	0644
regex	2861 bytes	0644
scoped_allocator	17649 bytes	0644
semaphore	3000 bytes	0644
set	3799 bytes	0644
shared_mutex	24588 bytes	0644
source_location	2747 bytes	0644
span	13131 bytes	0644
sstream	39231 bytes	0644
stack	2391 bytes	0644
stdexcept	9878 bytes	0644
stdlib.h	2248 bytes	0644
stop_token	15982 bytes	0644
streambuf	29890 bytes	0644
string	4645 bytes	0644
string_view	26157 bytes	0644
syncstream	8330 bytes	0644
system_error	15006 bytes	0644
tgmath.h	1360 bytes	0644
thread	5919 bytes	0644
tuple	62767 bytes	0644
type_traits	107667 bytes	0644
typeindex	3512 bytes	0644
typeinfo	7746 bytes	0644
unordered_map	3467 bytes	0644
unordered_set	3340 bytes	0644
utility	14816 bytes	0644
valarray	40695 bytes	0644
variant	62866 bytes	0644
vector	4275 bytes	0644
version	9264 bytes	0644
Command Bosku:

File Content: chrono

File Content: `chrono`
