chrono

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

// Copyright (C) 2008-2015 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.
 */

#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.

#ifdef _GLIBCXX_USE_C99_STDINT_TR1

namespace std _GLIBCXX_VISIBILITY(default)
{
  /**
   * @defgroup chrono Time
   * @ingroup utilities
   *
   * Classes and functions for time.
   * @{
   */

  /** @namespace std::chrono
   *  @brief ISO C++ 2011 entities sub-namespace for time and date.
   */
  namespace chrono
  {
  _GLIBCXX_BEGIN_NAMESPACE_VERSION

    template<typename _Rep, typename _Period = ratio<1>>
      struct duration;

    template<typename _Clock, typename _Dur = typename _Clock::duration>
      struct time_point;

  _GLIBCXX_END_NAMESPACE_VERSION
  }

_GLIBCXX_BEGIN_NAMESPACE_VERSION

  // 20.11.4.3 specialization of common_type (for duration, sfinae-friendly)
  
  template<typename _CT, typename _Period1, typename _Period2>
    struct __duration_common_type_wrapper
    {
    private:
      typedef __static_gcd<_Period1::num, _Period2::num> __gcd_num;
      typedef __static_gcd<_Period1::den, _Period2::den> __gcd_den;
      typedef typename _CT::type __cr;
      typedef ratio<__gcd_num::value,
        (_Period1::den / __gcd_den::value) * _Period2::den> __r;
    public:
      typedef __success_type<chrono::duration<__cr, __r>> type;
    };

  template<typename _Period1, typename _Period2>
    struct __duration_common_type_wrapper<__failure_type, _Period1, _Period2>
    { typedef __failure_type type; };

  template<typename _Rep1, typename _Period1, typename _Rep2, typename _Period2>
    struct common_type<chrono::duration<_Rep1, _Period1>,
             chrono::duration<_Rep2, _Period2>>
    : public __duration_common_type_wrapper<typename __member_type_wrapper<
             common_type<_Rep1, _Rep2>>::type, _Period1, _Period2>::type
    { };

  // 20.11.4.3 specialization of common_type (for time_point, sfinae-friendly)
  
  template<typename _CT, typename _Clock>
    struct __timepoint_common_type_wrapper
    {
      typedef __success_type<chrono::time_point<_Clock, typename _CT::type>>
        type;
    };

  template<typename _Clock>
    struct __timepoint_common_type_wrapper<__failure_type, _Clock>
    { typedef __failure_type type; };

  template<typename _Clock, typename _Duration1, typename _Duration2>
    struct common_type<chrono::time_point<_Clock, _Duration1>,
             chrono::time_point<_Clock, _Duration2>>
    : public __timepoint_common_type_wrapper<typename __member_type_wrapper<
             common_type<_Duration1, _Duration2>>::type, _Clock>::type
    { };

_GLIBCXX_END_NAMESPACE_VERSION

  namespace chrono
  {
  _GLIBCXX_BEGIN_NAMESPACE_VERSION

    // 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
      { };

    /// duration_cast
    template<typename _ToDur, typename _Rep, typename _Period>
      constexpr typename enable_if<__is_duration<_ToDur>::value,
                                   _ToDur>::type
      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>
      { };

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

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

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

    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
      { };

    /// duration
    template<typename _Rep, typename _Period>
      struct duration
      {
        typedef _Rep                                            rep;
        typedef _Period                                         period;

        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;

        // NB: Make constexpr implicit. This cannot be explicitly
        // constexpr, as any UDT that is not a literal type with a
        // constexpr copy constructor will be ill-formed.
        duration(const duration&) = default;

        template<typename _Rep2, typename = typename
               enable_if<is_convertible<_Rep2, rep>::value
                         && (treat_as_floating_point<rep>::value
                             || !treat_as_floating_point<_Rep2>::value)>::type>
          constexpr explicit duration(const _Rep2& __rep)
          : __r(static_cast<rep>(__rep)) { }

        template<typename _Rep2, typename _Period2, typename = typename
               enable_if<treat_as_floating_point<rep>::value
                         || (ratio_divide<_Period2, period>::den == 1
                             && !treat_as_floating_point<_Rep2>::value)>::type>
          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
        operator+() const
        { return *this; }

        constexpr duration
        operator-() const
        { return duration(-__r); }

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

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

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

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

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

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

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

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

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

        template<typename _Rep2 = rep>
          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()
        { return duration(duration_values<rep>::zero()); }

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

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

      private:
        rep __r;
      };

    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());
      }

    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());
      }

    template<typename _Rep1, typename _Rep2, bool =
             is_convertible<_Rep2,
                            typename common_type<_Rep1, _Rep2>::type>::value>
      struct __common_rep_type { };

    template<typename _Rep1, typename _Rep2>
      struct __common_rep_type<_Rep1, _Rep2, true>
      { typedef typename common_type<_Rep1, _Rep2>::type type; };

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

    template<typename _Rep1, typename _Period, typename _Rep2>
      constexpr duration<typename __common_rep_type<_Rep1, typename
        enable_if<!__is_duration<_Rep2>::value, _Rep2>::type>::type, _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<typename __common_rep_type<_Rep1, typename
        enable_if<!__is_duration<_Rep2>::value, _Rep2>::type>::type, _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
    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();
      }

    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); }

    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); }

    /// nanoseconds
    typedef duration<int64_t, nano>         nanoseconds;

    /// microseconds
    typedef duration<int64_t, micro>        microseconds;

    /// milliseconds
    typedef duration<int64_t, milli>        milliseconds;

    /// seconds
    typedef duration<int64_t>               seconds;

    /// minutes
    typedef duration<int64_t, ratio< 60>>   minutes;

    /// hours
    typedef duration<int64_t, ratio<3600>>  hours;

    /// time_point
    template<typename _Clock, typename _Dur>
      struct time_point
      {
        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; }

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

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

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

        static constexpr time_point
        max()
        { 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()));
      }

    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);
      }

    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); 
      }

    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); 
      }

    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(); }

    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 !(__lhs == __rhs); }

    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 higest
    // 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.
    */
    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.
    */
    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.
    */
    using high_resolution_clock = system_clock;

    } // end inline namespace _V2

  _GLIBCXX_END_NAMESPACE_VERSION
  } // namespace chrono

#if __cplusplus > 201103L

#define __cpp_lib_chrono_udls 201304

  inline namespace literals
  {
  inline namespace chrono_literals
  {
  _GLIBCXX_BEGIN_NAMESPACE_VERSION

    template<typename _Rep, unsigned long long _Val>
      struct _Checked_integral_constant
      : integral_constant<_Rep, static_cast<_Rep>(_Val)>
      {
        static_assert(_Checked_integral_constant::value >= 0
                      && _Checked_integral_constant::value == _Val,
                      "literal value cannot be represented by duration type");
      };

    template<typename _Dur, char... _Digits>
      constexpr _Dur __check_overflow()
      {
        using _Val = __parse_int::_Parse_int<_Digits...>;
        using _Rep = typename _Dur::rep;
        // TODO: should be simply integral_constant<_Rep, _Val::value>
        // but GCC doesn't reject narrowing conversions to _Rep.
        using _CheckedVal = _Checked_integral_constant<_Rep, _Val::value>;
        return _Dur{_CheckedVal::value};
      }

    constexpr chrono::duration<long double, ratio<3600,1>>
    operator""h(long double __hours)
    { return chrono::duration<long double, ratio<3600,1>>{__hours}; }

    template <char... _Digits>
      constexpr chrono::hours
      operator""h()
      { return __check_overflow<chrono::hours, _Digits...>(); }

    constexpr chrono::duration<long double, ratio<60,1>>
    operator""min(long double __mins)
    { return chrono::duration<long double, ratio<60,1>>{__mins}; }

    template <char... _Digits>
      constexpr chrono::minutes
      operator""min()
      { return __check_overflow<chrono::minutes, _Digits...>(); }

    constexpr chrono::duration<long double>
    operator""s(long double __secs)
    { return chrono::duration<long double>{__secs}; }

    template <char... _Digits>
      constexpr chrono::seconds
      operator""s()
      { return __check_overflow<chrono::seconds, _Digits...>(); }

    constexpr chrono::duration<long double, milli>
    operator""ms(long double __msecs)
    { return chrono::duration<long double, milli>{__msecs}; }

    template <char... _Digits>
      constexpr chrono::milliseconds
      operator""ms()
      { return __check_overflow<chrono::milliseconds, _Digits...>(); }

    constexpr chrono::duration<long double, micro>
    operator""us(long double __usecs)
    { return chrono::duration<long double, micro>{__usecs}; }

    template <char... _Digits>
      constexpr chrono::microseconds
      operator""us()
      { return __check_overflow<chrono::microseconds, _Digits...>(); }

    constexpr chrono::duration<long double, nano>
    operator""ns(long double __nsecs)
    { return chrono::duration<long double, nano>{__nsecs}; }

    template <char... _Digits>
      constexpr chrono::nanoseconds
      operator""ns()
      { return __check_overflow<chrono::nanoseconds, _Digits...>(); }

  _GLIBCXX_END_NAMESPACE_VERSION
  } // inline namespace chrono_literals
  } // inline namespace literals

  namespace chrono
  {
  _GLIBCXX_BEGIN_NAMESPACE_VERSION

  using namespace literals::chrono_literals;

  _GLIBCXX_END_NAMESPACE_VERSION
  } // namespace chrono

#endif // __cplusplus > 201103L

  // @} group chrono
} // namespace std

#endif //_GLIBCXX_USE_C99_STDINT_TR1

#endif // C++11

#endif //_GLIBCXX_CHRONO