1 // <chrono> -*- C++ -*-
2 
3 // Copyright (C) 2008-2020 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library.  This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file include/chrono
26  *  This is a Standard C++ Library header.
27  *  @ingroup chrono
28  */
29 
30 #ifndef _GLIBCXX_CHRONO
31 #define _GLIBCXX_CHRONO 1
32 
33 #pragma GCC system_header
34 
35 #if __cplusplus < 201103L
36 # include <bits/c++0x_warning.h>
37 #else
38 
39 #include <ratio>
40 #include <type_traits>
41 #include <limits>
42 #include <ctime>
43 #include <bits/parse_numbers.h> // for literals support.
44 #if __cplusplus > 201703L
45 # include <concepts>
46 # include <compare>
47 #endif
48 
49 namespace std _GLIBCXX_VISIBILITY(default)
50 {
51 _GLIBCXX_BEGIN_NAMESPACE_VERSION
52 
53 #if __cplusplus >= 201703L
54   namespace filesystem { struct __file_clock; };
55 #endif
56 
57   /**
58    * @defgroup chrono Time
59    * @ingroup utilities
60    *
61    * Classes and functions for time.
62    * @{
63    */
64 
65   /** @namespace std::chrono
66    *  @brief ISO C++ 2011 namespace for date and time utilities
67    */
68   namespace chrono
69   {
70     template<typename _Rep, typename _Period = ratio<1>>
71       struct duration;
72 
73     template<typename _Clock, typename _Dur = typename _Clock::duration>
74       struct time_point;
75   }
76 
77   // 20.11.4.3 specialization of common_type (for duration, sfinae-friendly)
78 
79   /// @cond undocumented
80 
81   template<typename _CT, typename _Period1, typename _Period2, typename = void>
82     struct __duration_common_type
83     { };
84 
85   template<typename _CT, typename _Period1, typename _Period2>
86     struct __duration_common_type<_CT, _Period1, _Period2,
87 				  __void_t<typename _CT::type>>
88     {
89     private:
90       using __gcd_num = __static_gcd<_Period1::num, _Period2::num>;
91       using __gcd_den = __static_gcd<_Period1::den, _Period2::den>;
92       using __cr = typename _CT::type;
93       using __r = ratio<__gcd_num::value,
94 			(_Period1::den / __gcd_den::value) * _Period2::den>;
95 
96     public:
97       using type = chrono::duration<__cr, typename __r::type>;
98     };
99 
100   /// @endcond
101 
102   /// Specialization of common_type for chrono::duration types.
103   /// @relates duration
104   template<typename _Rep1, typename _Period1, typename _Rep2, typename _Period2>
105     struct common_type<chrono::duration<_Rep1, _Period1>,
106 		       chrono::duration<_Rep2, _Period2>>
107     : __duration_common_type<common_type<_Rep1, _Rep2>,
108 			     typename _Period1::type,
109 			     typename _Period2::type>
110     { };
111 
112   /// Specialization of common_type for two identical chrono::duration types.
113   /// @relates duration
114   template<typename _Rep, typename _Period>
115     struct common_type<chrono::duration<_Rep, _Period>,
116 		       chrono::duration<_Rep, _Period>>
117     {
118       using type = chrono::duration<typename common_type<_Rep>::type,
119 				    typename _Period::type>;
120     };
121 
122   /// Specialization of common_type for one chrono::duration type.
123   /// @relates duration
124   template<typename _Rep, typename _Period>
125     struct common_type<chrono::duration<_Rep, _Period>>
126     {
127       using type = chrono::duration<typename common_type<_Rep>::type,
128 				    typename _Period::type>;
129     };
130 
131   // 20.11.4.3 specialization of common_type (for time_point, sfinae-friendly)
132 
133   /// @cond undocumented
134 
135   template<typename _CT, typename _Clock, typename = void>
136     struct __timepoint_common_type
137     { };
138 
139   template<typename _CT, typename _Clock>
140     struct __timepoint_common_type<_CT, _Clock, __void_t<typename _CT::type>>
141     {
142       using type = chrono::time_point<_Clock, typename _CT::type>;
143     };
144 
145   /// @endcond
146 
147   /// Specialization of common_type for chrono::time_point types.
148   /// @relates time_point
149   template<typename _Clock, typename _Duration1, typename _Duration2>
150     struct common_type<chrono::time_point<_Clock, _Duration1>,
151 		       chrono::time_point<_Clock, _Duration2>>
152     : __timepoint_common_type<common_type<_Duration1, _Duration2>, _Clock>
153     { };
154 
155   /// Specialization of common_type for two identical chrono::time_point types.
156   /// @relates time_point
157   template<typename _Clock, typename _Duration>
158     struct common_type<chrono::time_point<_Clock, _Duration>,
159 		       chrono::time_point<_Clock, _Duration>>
160     { using type = chrono::time_point<_Clock, _Duration>; };
161 
162   /// Specialization of common_type for one chrono::time_point type.
163   /// @relates time_point
164   template<typename _Clock, typename _Duration>
165     struct common_type<chrono::time_point<_Clock, _Duration>>
166     { using type = chrono::time_point<_Clock, _Duration>; };
167 
168   /// @} group chrono
169 
170   namespace chrono
171   {
172     /// @addtogroup chrono
173     /// @{
174 
175     /// @cond undocumented
176 
177     // Primary template for duration_cast impl.
178     template<typename _ToDur, typename _CF, typename _CR,
179 	     bool _NumIsOne = false, bool _DenIsOne = false>
180       struct __duration_cast_impl
181       {
182 	template<typename _Rep, typename _Period>
183 	  static constexpr _ToDur
184 	  __cast(const duration<_Rep, _Period>& __d)
185 	  {
186 	    typedef typename _ToDur::rep			__to_rep;
187 	    return _ToDur(static_cast<__to_rep>(static_cast<_CR>(__d.count())
188 	      * static_cast<_CR>(_CF::num)
189 	      / static_cast<_CR>(_CF::den)));
190 	  }
191       };
192 
193     template<typename _ToDur, typename _CF, typename _CR>
194       struct __duration_cast_impl<_ToDur, _CF, _CR, true, true>
195       {
196 	template<typename _Rep, typename _Period>
197 	  static constexpr _ToDur
198 	  __cast(const duration<_Rep, _Period>& __d)
199 	  {
200 	    typedef typename _ToDur::rep			__to_rep;
201 	    return _ToDur(static_cast<__to_rep>(__d.count()));
202 	  }
203       };
204 
205     template<typename _ToDur, typename _CF, typename _CR>
206       struct __duration_cast_impl<_ToDur, _CF, _CR, true, false>
207       {
208 	template<typename _Rep, typename _Period>
209 	  static constexpr _ToDur
210 	  __cast(const duration<_Rep, _Period>& __d)
211 	  {
212 	    typedef typename _ToDur::rep			__to_rep;
213 	    return _ToDur(static_cast<__to_rep>(
214 	      static_cast<_CR>(__d.count()) / static_cast<_CR>(_CF::den)));
215 	  }
216       };
217 
218     template<typename _ToDur, typename _CF, typename _CR>
219       struct __duration_cast_impl<_ToDur, _CF, _CR, false, true>
220       {
221 	template<typename _Rep, typename _Period>
222 	  static constexpr _ToDur
223 	  __cast(const duration<_Rep, _Period>& __d)
224 	  {
225 	    typedef typename _ToDur::rep			__to_rep;
226 	    return _ToDur(static_cast<__to_rep>(
227 	      static_cast<_CR>(__d.count()) * static_cast<_CR>(_CF::num)));
228 	  }
229       };
230 
231     template<typename _Tp>
232       struct __is_duration
233       : std::false_type
234       { };
235 
236     template<typename _Rep, typename _Period>
237       struct __is_duration<duration<_Rep, _Period>>
238       : std::true_type
239       { };
240 
241     template<typename _Tp>
242       using __enable_if_is_duration
243 	= typename enable_if<__is_duration<_Tp>::value, _Tp>::type;
244 
245     template<typename _Tp>
246       using __disable_if_is_duration
247 	= typename enable_if<!__is_duration<_Tp>::value, _Tp>::type;
248 
249     /// @endcond
250 
251     /// duration_cast
252     template<typename _ToDur, typename _Rep, typename _Period>
253       constexpr __enable_if_is_duration<_ToDur>
254       duration_cast(const duration<_Rep, _Period>& __d)
255       {
256 	typedef typename _ToDur::period				__to_period;
257 	typedef typename _ToDur::rep				__to_rep;
258 	typedef ratio_divide<_Period, __to_period> 		__cf;
259 	typedef typename common_type<__to_rep, _Rep, intmax_t>::type
260 	  							__cr;
261 	typedef  __duration_cast_impl<_ToDur, __cf, __cr,
262 				      __cf::num == 1, __cf::den == 1> __dc;
263 	return __dc::__cast(__d);
264       }
265 
266     /// treat_as_floating_point
267     template<typename _Rep>
268       struct treat_as_floating_point
269       : is_floating_point<_Rep>
270       { };
271 
272 #if __cplusplus > 201402L
273     template <typename _Rep>
274       inline constexpr bool treat_as_floating_point_v =
275         treat_as_floating_point<_Rep>::value;
276 #endif // C++17
277 
278 #if __cplusplus > 201703L
279     template<typename _Tp>
280       struct is_clock;
281 
282     template<typename _Tp>
283       inline constexpr bool is_clock_v = is_clock<_Tp>::value;
284 
285 #if __cpp_lib_concepts
286     template<typename _Tp>
287       struct is_clock : false_type
288       { };
289 
290     template<typename _Tp>
291       requires requires {
292 	typename _Tp::rep;
293 	typename _Tp::period;
294 	typename _Tp::duration;
295 	typename _Tp::time_point::clock;
296 	typename _Tp::time_point::duration;
297 	{ &_Tp::is_steady } -> same_as<const bool*>;
298 	{ _Tp::now() } -> same_as<typename _Tp::time_point>;
299 	requires same_as<typename _Tp::duration,
300 			 duration<typename _Tp::rep, typename _Tp::period>>;
301 	requires same_as<typename _Tp::time_point::duration,
302 			 typename _Tp::duration>;
303       }
304       struct is_clock<_Tp> : true_type
305       { };
306 #else
307     template<typename _Tp, typename = void>
308       struct __is_clock_impl : false_type
309       { };
310 
311     template<typename _Tp>
312       struct __is_clock_impl<_Tp,
313 			     void_t<typename _Tp::rep, typename _Tp::period,
314 				    typename _Tp::duration,
315 				    typename _Tp::time_point::duration,
316 				    decltype(_Tp::is_steady),
317 				    decltype(_Tp::now())>>
318       : __and_<is_same<typename _Tp::duration,
319 		       duration<typename _Tp::rep, typename _Tp::period>>,
320 	       is_same<typename _Tp::time_point::duration,
321 		       typename _Tp::duration>,
322 	       is_same<decltype(&_Tp::is_steady), const bool*>,
323 	       is_same<decltype(_Tp::now()), typename _Tp::time_point>>::type
324       { };
325 
326     template<typename _Tp>
327       struct is_clock : __is_clock_impl<_Tp>::type
328       { };
329 #endif
330 #endif // C++20
331 
332 #if __cplusplus >= 201703L
333 # define __cpp_lib_chrono 201611
334 
335     template<typename _ToDur, typename _Rep, typename _Period>
336       constexpr __enable_if_is_duration<_ToDur>
337       floor(const duration<_Rep, _Period>& __d)
338       {
339 	auto __to = chrono::duration_cast<_ToDur>(__d);
340 	if (__to > __d)
341 	  return __to - _ToDur{1};
342 	return __to;
343       }
344 
345     template<typename _ToDur, typename _Rep, typename _Period>
346       constexpr __enable_if_is_duration<_ToDur>
347       ceil(const duration<_Rep, _Period>& __d)
348       {
349 	auto __to = chrono::duration_cast<_ToDur>(__d);
350 	if (__to < __d)
351 	  return __to + _ToDur{1};
352 	return __to;
353       }
354 
355     template <typename _ToDur, typename _Rep, typename _Period>
356       constexpr enable_if_t<
357 	__and_<__is_duration<_ToDur>,
358 	       __not_<treat_as_floating_point<typename _ToDur::rep>>>::value,
359 	_ToDur>
360       round(const duration<_Rep, _Period>& __d)
361       {
362 	_ToDur __t0 = chrono::floor<_ToDur>(__d);
363 	_ToDur __t1 = __t0 + _ToDur{1};
364 	auto __diff0 = __d - __t0;
365 	auto __diff1 = __t1 - __d;
366 	if (__diff0 == __diff1)
367 	{
368 	    if (__t0.count() & 1)
369 		return __t1;
370 	    return __t0;
371 	}
372 	else if (__diff0 < __diff1)
373 	    return __t0;
374 	return __t1;
375       }
376 
377     template<typename _Rep, typename _Period>
378       constexpr
379       enable_if_t<numeric_limits<_Rep>::is_signed, duration<_Rep, _Period>>
380       abs(duration<_Rep, _Period> __d)
381       {
382 	if (__d >= __d.zero())
383 	  return __d;
384 	return -__d;
385       }
386 #endif // C++17
387 
388     /// duration_values
389     template<typename _Rep>
390       struct duration_values
391       {
392 	static constexpr _Rep
393 	zero() noexcept
394 	{ return _Rep(0); }
395 
396 	static constexpr _Rep
397 	max() noexcept
398 	{ return numeric_limits<_Rep>::max(); }
399 
400 	static constexpr _Rep
401 	min() noexcept
402 	{ return numeric_limits<_Rep>::lowest(); }
403       };
404 
405     /// @cond undocumented
406 
407     template<typename _Tp>
408       struct __is_ratio
409       : std::false_type
410       { };
411 
412     template<intmax_t _Num, intmax_t _Den>
413       struct __is_ratio<ratio<_Num, _Den>>
414       : std::true_type
415       { };
416 
417     /// @endcond
418 
419     /// duration
420     template<typename _Rep, typename _Period>
421       struct duration
422       {
423       private:
424 	template<typename _Rep2>
425 	  using __is_float = treat_as_floating_point<_Rep2>;
426 
427 	static constexpr intmax_t
428 	_S_gcd(intmax_t __m, intmax_t __n) noexcept
429 	{
430 	  // Duration only allows positive periods so we don't need to
431 	  // support negative values here (unlike __static_gcd and std::gcd).
432 	  return (__m == 0) ? __n : (__n == 0) ? __m : _S_gcd(__n, __m % __n);
433 	}
434 
435 	// _GLIBCXX_RESOLVE_LIB_DEFECTS
436 	// 2094. overflow shouldn't participate in overload resolution
437 	// 3090. What is [2094] intended to mean?
438 	// This only produces a valid type if no overflow occurs.
439 	template<typename _R1, typename _R2,
440 		 intmax_t __gcd1 = _S_gcd(_R1::num, _R2::num),
441 		 intmax_t __gcd2 = _S_gcd(_R1::den, _R2::den)>
442 	  using __divide = ratio<(_R1::num / __gcd1) * (_R2::den / __gcd2),
443 				 (_R1::den / __gcd2) * (_R2::num / __gcd1)>;
444 
445 	// _Period2 is an exact multiple of _Period
446 	template<typename _Period2>
447 	  using __is_harmonic
448 	    = __bool_constant<__divide<_Period2, _Period>::den == 1>;
449 
450       public:
451 
452 	using rep = _Rep;
453 	using period = typename _Period::type;
454 
455 	static_assert(!__is_duration<_Rep>::value, "rep cannot be a duration");
456 	static_assert(__is_ratio<_Period>::value,
457 		      "period must be a specialization of ratio");
458 	static_assert(_Period::num > 0, "period must be positive");
459 
460 	// 20.11.5.1 construction / copy / destroy
461 	constexpr duration() = default;
462 
463 	duration(const duration&) = default;
464 
465 	// _GLIBCXX_RESOLVE_LIB_DEFECTS
466 	// 3050. Conversion specification problem in chrono::duration
467 	template<typename _Rep2, typename = _Require<
468 		 is_convertible<const _Rep2&, rep>,
469 		 __or_<__is_float<rep>, __not_<__is_float<_Rep2>>>>>
470 	  constexpr explicit duration(const _Rep2& __rep)
471 	  : __r(static_cast<rep>(__rep)) { }
472 
473 	template<typename _Rep2, typename _Period2, typename = _Require<
474 		 is_convertible<const _Rep2&, rep>,
475 		 __or_<__is_float<rep>,
476 		       __and_<__is_harmonic<_Period2>,
477 			      __not_<__is_float<_Rep2>>>>>>
478 	  constexpr duration(const duration<_Rep2, _Period2>& __d)
479 	  : __r(duration_cast<duration>(__d).count()) { }
480 
481 	~duration() = default;
482 	duration& operator=(const duration&) = default;
483 
484 	// 20.11.5.2 observer
485 	constexpr rep
486 	count() const
487 	{ return __r; }
488 
489 	// 20.11.5.3 arithmetic
490 
491 	constexpr duration<typename common_type<rep>::type, period>
492 	operator+() const
493 	{ return duration<typename common_type<rep>::type, period>(__r); }
494 
495 	constexpr duration<typename common_type<rep>::type, period>
496 	operator-() const
497 	{ return duration<typename common_type<rep>::type, period>(-__r); }
498 
499 	_GLIBCXX17_CONSTEXPR duration&
500 	operator++()
501 	{
502 	  ++__r;
503 	  return *this;
504 	}
505 
506 	_GLIBCXX17_CONSTEXPR duration
507 	operator++(int)
508 	{ return duration(__r++); }
509 
510 	_GLIBCXX17_CONSTEXPR duration&
511 	operator--()
512 	{
513 	  --__r;
514 	  return *this;
515 	}
516 
517 	_GLIBCXX17_CONSTEXPR duration
518 	operator--(int)
519 	{ return duration(__r--); }
520 
521 	_GLIBCXX17_CONSTEXPR duration&
522 	operator+=(const duration& __d)
523 	{
524 	  __r += __d.count();
525 	  return *this;
526 	}
527 
528 	_GLIBCXX17_CONSTEXPR duration&
529 	operator-=(const duration& __d)
530 	{
531 	  __r -= __d.count();
532 	  return *this;
533 	}
534 
535 	_GLIBCXX17_CONSTEXPR duration&
536 	operator*=(const rep& __rhs)
537 	{
538 	  __r *= __rhs;
539 	  return *this;
540 	}
541 
542 	_GLIBCXX17_CONSTEXPR duration&
543 	operator/=(const rep& __rhs)
544 	{
545 	  __r /= __rhs;
546 	  return *this;
547 	}
548 
549 	// DR 934.
550 	template<typename _Rep2 = rep>
551 	  _GLIBCXX17_CONSTEXPR
552 	  typename enable_if<!treat_as_floating_point<_Rep2>::value,
553 			     duration&>::type
554 	  operator%=(const rep& __rhs)
555 	  {
556 	    __r %= __rhs;
557 	    return *this;
558 	  }
559 
560 	template<typename _Rep2 = rep>
561 	  _GLIBCXX17_CONSTEXPR
562 	  typename enable_if<!treat_as_floating_point<_Rep2>::value,
563 			     duration&>::type
564 	  operator%=(const duration& __d)
565 	  {
566 	    __r %= __d.count();
567 	    return *this;
568 	  }
569 
570 	// 20.11.5.4 special values
571 	static constexpr duration
572 	zero() noexcept
573 	{ return duration(duration_values<rep>::zero()); }
574 
575 	static constexpr duration
576 	min() noexcept
577 	{ return duration(duration_values<rep>::min()); }
578 
579 	static constexpr duration
580 	max() noexcept
581 	{ return duration(duration_values<rep>::max()); }
582 
583       private:
584 	rep __r;
585       };
586 
587     /// @relates duration @{
588 
589     /// The sum of two durations.
590     template<typename _Rep1, typename _Period1,
591 	     typename _Rep2, typename _Period2>
592       constexpr typename common_type<duration<_Rep1, _Period1>,
593 				     duration<_Rep2, _Period2>>::type
594       operator+(const duration<_Rep1, _Period1>& __lhs,
595 		const duration<_Rep2, _Period2>& __rhs)
596       {
597 	typedef duration<_Rep1, _Period1>			__dur1;
598 	typedef duration<_Rep2, _Period2>			__dur2;
599 	typedef typename common_type<__dur1,__dur2>::type	__cd;
600 	return __cd(__cd(__lhs).count() + __cd(__rhs).count());
601       }
602 
603     /// The difference between two durations.
604     template<typename _Rep1, typename _Period1,
605 	     typename _Rep2, typename _Period2>
606       constexpr typename common_type<duration<_Rep1, _Period1>,
607 				     duration<_Rep2, _Period2>>::type
608       operator-(const duration<_Rep1, _Period1>& __lhs,
609 		const duration<_Rep2, _Period2>& __rhs)
610       {
611 	typedef duration<_Rep1, _Period1>			__dur1;
612 	typedef duration<_Rep2, _Period2>			__dur2;
613 	typedef typename common_type<__dur1,__dur2>::type	__cd;
614 	return __cd(__cd(__lhs).count() - __cd(__rhs).count());
615       }
616 
617     /// @}
618 
619     /// @cond undocumented
620 
621     // SFINAE helper to obtain common_type<_Rep1, _Rep2> only if _Rep2
622     // is implicitly convertible to it.
623     // _GLIBCXX_RESOLVE_LIB_DEFECTS
624     // 3050. Conversion specification problem in chrono::duration constructor
625     template<typename _Rep1, typename _Rep2,
626 	     typename _CRep = typename common_type<_Rep1, _Rep2>::type>
627       using __common_rep_t = typename
628 	enable_if<is_convertible<const _Rep2&, _CRep>::value, _CRep>::type;
629 
630     /// @endcond
631 
632     /// @relates duration @{
633 
634     /// Multiply a duration by a scalar value.
635     template<typename _Rep1, typename _Period, typename _Rep2>
636       constexpr duration<__common_rep_t<_Rep1, _Rep2>, _Period>
637       operator*(const duration<_Rep1, _Period>& __d, const _Rep2& __s)
638       {
639 	typedef duration<typename common_type<_Rep1, _Rep2>::type, _Period>
640 	  __cd;
641 	return __cd(__cd(__d).count() * __s);
642       }
643 
644     /// Multiply a duration by a scalar value.
645     template<typename _Rep1, typename _Rep2, typename _Period>
646       constexpr duration<__common_rep_t<_Rep2, _Rep1>, _Period>
647       operator*(const _Rep1& __s, const duration<_Rep2, _Period>& __d)
648       { return __d * __s; }
649 
650     template<typename _Rep1, typename _Period, typename _Rep2>
651       constexpr
652       duration<__common_rep_t<_Rep1, __disable_if_is_duration<_Rep2>>, _Period>
653       operator/(const duration<_Rep1, _Period>& __d, const _Rep2& __s)
654       {
655 	typedef duration<typename common_type<_Rep1, _Rep2>::type, _Period>
656 	  __cd;
657 	return __cd(__cd(__d).count() / __s);
658       }
659 
660     template<typename _Rep1, typename _Period1,
661 	     typename _Rep2, typename _Period2>
662       constexpr typename common_type<_Rep1, _Rep2>::type
663       operator/(const duration<_Rep1, _Period1>& __lhs,
664 		const duration<_Rep2, _Period2>& __rhs)
665       {
666 	typedef duration<_Rep1, _Period1>			__dur1;
667 	typedef duration<_Rep2, _Period2>			__dur2;
668 	typedef typename common_type<__dur1,__dur2>::type	__cd;
669 	return __cd(__lhs).count() / __cd(__rhs).count();
670       }
671 
672     // DR 934.
673     template<typename _Rep1, typename _Period, typename _Rep2>
674       constexpr
675       duration<__common_rep_t<_Rep1, __disable_if_is_duration<_Rep2>>, _Period>
676       operator%(const duration<_Rep1, _Period>& __d, const _Rep2& __s)
677       {
678 	typedef duration<typename common_type<_Rep1, _Rep2>::type, _Period>
679 	  __cd;
680 	return __cd(__cd(__d).count() % __s);
681       }
682 
683     template<typename _Rep1, typename _Period1,
684 	     typename _Rep2, typename _Period2>
685       constexpr typename common_type<duration<_Rep1, _Period1>,
686 				     duration<_Rep2, _Period2>>::type
687       operator%(const duration<_Rep1, _Period1>& __lhs,
688 		const duration<_Rep2, _Period2>& __rhs)
689       {
690 	typedef duration<_Rep1, _Period1>			__dur1;
691 	typedef duration<_Rep2, _Period2>			__dur2;
692 	typedef typename common_type<__dur1,__dur2>::type	__cd;
693 	return __cd(__cd(__lhs).count() % __cd(__rhs).count());
694       }
695 
696     // comparisons
697 
698     template<typename _Rep1, typename _Period1,
699 	     typename _Rep2, typename _Period2>
700       constexpr bool
701       operator==(const duration<_Rep1, _Period1>& __lhs,
702 		 const duration<_Rep2, _Period2>& __rhs)
703       {
704 	typedef duration<_Rep1, _Period1>			__dur1;
705 	typedef duration<_Rep2, _Period2>			__dur2;
706 	typedef typename common_type<__dur1,__dur2>::type	__ct;
707 	return __ct(__lhs).count() == __ct(__rhs).count();
708       }
709 
710     template<typename _Rep1, typename _Period1,
711 	     typename _Rep2, typename _Period2>
712       constexpr bool
713       operator<(const duration<_Rep1, _Period1>& __lhs,
714 		const duration<_Rep2, _Period2>& __rhs)
715       {
716 	typedef duration<_Rep1, _Period1>			__dur1;
717 	typedef duration<_Rep2, _Period2>			__dur2;
718 	typedef typename common_type<__dur1,__dur2>::type	__ct;
719 	return __ct(__lhs).count() < __ct(__rhs).count();
720       }
721 
722 #if __cpp_lib_three_way_comparison
723     template<typename _Rep1, typename _Period1,
724 	     typename _Rep2, typename _Period2>
725       requires three_way_comparable<common_type_t<_Rep1, _Rep2>>
726       constexpr auto
727       operator<=>(const duration<_Rep1, _Period1>& __lhs,
728 		  const duration<_Rep2, _Period2>& __rhs)
729       {
730 	using __ct = common_type_t<duration<_Rep1, _Period1>,
731 				   duration<_Rep2, _Period2>>;
732 	return __ct(__lhs).count() <=> __ct(__rhs).count();
733       }
734 #else
735     template<typename _Rep1, typename _Period1,
736 	     typename _Rep2, typename _Period2>
737       constexpr bool
738       operator!=(const duration<_Rep1, _Period1>& __lhs,
739 		 const duration<_Rep2, _Period2>& __rhs)
740       { return !(__lhs == __rhs); }
741 #endif
742 
743     template<typename _Rep1, typename _Period1,
744 	     typename _Rep2, typename _Period2>
745       constexpr bool
746       operator<=(const duration<_Rep1, _Period1>& __lhs,
747 		 const duration<_Rep2, _Period2>& __rhs)
748       { return !(__rhs < __lhs); }
749 
750     template<typename _Rep1, typename _Period1,
751 	     typename _Rep2, typename _Period2>
752       constexpr bool
753       operator>(const duration<_Rep1, _Period1>& __lhs,
754 		const duration<_Rep2, _Period2>& __rhs)
755       { return __rhs < __lhs; }
756 
757     template<typename _Rep1, typename _Period1,
758 	     typename _Rep2, typename _Period2>
759       constexpr bool
760       operator>=(const duration<_Rep1, _Period1>& __lhs,
761 		 const duration<_Rep2, _Period2>& __rhs)
762       { return !(__lhs < __rhs); }
763 
764     /// @}
765 
766 #ifdef _GLIBCXX_USE_C99_STDINT_TR1
767 # define _GLIBCXX_CHRONO_INT64_T int64_t
768 #elif defined __INT64_TYPE__
769 # define _GLIBCXX_CHRONO_INT64_T __INT64_TYPE__
770 #else
771     static_assert(std::numeric_limits<unsigned long long>::digits >= 64,
772 	"Representation type for nanoseconds must have at least 64 bits");
773 # define _GLIBCXX_CHRONO_INT64_T long long
774 #endif
775 
776     /// nanoseconds
777     using nanoseconds	= duration<_GLIBCXX_CHRONO_INT64_T, nano>;
778 
779     /// microseconds
780     using microseconds	= duration<_GLIBCXX_CHRONO_INT64_T, micro>;
781 
782     /// milliseconds
783     using milliseconds	= duration<_GLIBCXX_CHRONO_INT64_T, milli>;
784 
785     /// seconds
786     using seconds	= duration<_GLIBCXX_CHRONO_INT64_T>;
787 
788     /// minutes
789     using minutes	= duration<_GLIBCXX_CHRONO_INT64_T, ratio< 60>>;
790 
791     /// hours
792     using hours		= duration<_GLIBCXX_CHRONO_INT64_T, ratio<3600>>;
793 
794 #if __cplusplus > 201703L
795     /// days
796     using days		= duration<_GLIBCXX_CHRONO_INT64_T, ratio<86400>>;
797 
798     /// weeks
799     using weeks		= duration<_GLIBCXX_CHRONO_INT64_T, ratio<604800>>;
800 
801     /// years
802     using years		= duration<_GLIBCXX_CHRONO_INT64_T, ratio<31556952>>;
803 
804     /// months
805     using months	= duration<_GLIBCXX_CHRONO_INT64_T, ratio<2629746>>;
806 #endif // C++20
807 
808 #undef _GLIBCXX_CHRONO_INT64_T
809 
810     /// time_point
811     template<typename _Clock, typename _Dur>
812       struct time_point
813       {
814 	static_assert(__is_duration<_Dur>::value,
815 	    "duration must be a specialization of std::chrono::duration");
816 
817 	typedef _Clock						clock;
818 	typedef _Dur						duration;
819 	typedef typename duration::rep				rep;
820 	typedef typename duration::period			period;
821 
822 	constexpr time_point() : __d(duration::zero())
823 	{ }
824 
825 	constexpr explicit time_point(const duration& __dur)
826 	: __d(__dur)
827 	{ }
828 
829 	// conversions
830 	template<typename _Dur2,
831 		 typename = _Require<is_convertible<_Dur2, _Dur>>>
832 	  constexpr time_point(const time_point<clock, _Dur2>& __t)
833 	  : __d(__t.time_since_epoch())
834 	  { }
835 
836 	// observer
837 	constexpr duration
838 	time_since_epoch() const
839 	{ return __d; }
840 
841 	// arithmetic
842 	_GLIBCXX17_CONSTEXPR time_point&
843 	operator+=(const duration& __dur)
844 	{
845 	  __d += __dur;
846 	  return *this;
847 	}
848 
849 	_GLIBCXX17_CONSTEXPR time_point&
850 	operator-=(const duration& __dur)
851 	{
852 	  __d -= __dur;
853 	  return *this;
854 	}
855 
856 	// special values
857 	static constexpr time_point
858 	min() noexcept
859 	{ return time_point(duration::min()); }
860 
861 	static constexpr time_point
862 	max() noexcept
863 	{ return time_point(duration::max()); }
864 
865       private:
866 	duration __d;
867       };
868 
869     /// time_point_cast
870     template<typename _ToDur, typename _Clock, typename _Dur>
871       constexpr typename enable_if<__is_duration<_ToDur>::value,
872 				   time_point<_Clock, _ToDur>>::type
873       time_point_cast(const time_point<_Clock, _Dur>& __t)
874       {
875 	typedef time_point<_Clock, _ToDur>			__time_point;
876 	return __time_point(duration_cast<_ToDur>(__t.time_since_epoch()));
877       }
878 
879 #if __cplusplus > 201402L
880     template<typename _ToDur, typename _Clock, typename _Dur>
881       constexpr
882       enable_if_t<__is_duration<_ToDur>::value, time_point<_Clock, _ToDur>>
883       floor(const time_point<_Clock, _Dur>& __tp)
884       {
885 	return time_point<_Clock, _ToDur>{
886 	    chrono::floor<_ToDur>(__tp.time_since_epoch())};
887       }
888 
889     template<typename _ToDur, typename _Clock, typename _Dur>
890       constexpr
891       enable_if_t<__is_duration<_ToDur>::value, time_point<_Clock, _ToDur>>
892       ceil(const time_point<_Clock, _Dur>& __tp)
893       {
894 	return time_point<_Clock, _ToDur>{
895 	    chrono::ceil<_ToDur>(__tp.time_since_epoch())};
896       }
897 
898     template<typename _ToDur, typename _Clock, typename _Dur>
899       constexpr enable_if_t<
900 	__and_<__is_duration<_ToDur>,
901 	       __not_<treat_as_floating_point<typename _ToDur::rep>>>::value,
902 	time_point<_Clock, _ToDur>>
903       round(const time_point<_Clock, _Dur>& __tp)
904       {
905 	return time_point<_Clock, _ToDur>{
906 	    chrono::round<_ToDur>(__tp.time_since_epoch())};
907       }
908 #endif // C++17
909 
910     /// @relates time_point @{
911 
912     /// Adjust a time point forwards by the given duration.
913     template<typename _Clock, typename _Dur1,
914 	     typename _Rep2, typename _Period2>
915       constexpr time_point<_Clock,
916 	typename common_type<_Dur1, duration<_Rep2, _Period2>>::type>
917       operator+(const time_point<_Clock, _Dur1>& __lhs,
918 		const duration<_Rep2, _Period2>& __rhs)
919       {
920 	typedef duration<_Rep2, _Period2>			__dur2;
921 	typedef typename common_type<_Dur1,__dur2>::type	__ct;
922 	typedef time_point<_Clock, __ct>			__time_point;
923 	return __time_point(__lhs.time_since_epoch() + __rhs);
924       }
925 
926     /// Adjust a time point forwards by the given duration.
927     template<typename _Rep1, typename _Period1,
928 	     typename _Clock, typename _Dur2>
929       constexpr time_point<_Clock,
930 	typename common_type<duration<_Rep1, _Period1>, _Dur2>::type>
931       operator+(const duration<_Rep1, _Period1>& __lhs,
932 		const time_point<_Clock, _Dur2>& __rhs)
933       {
934 	typedef duration<_Rep1, _Period1>			__dur1;
935 	typedef typename common_type<__dur1,_Dur2>::type	__ct;
936 	typedef time_point<_Clock, __ct>			__time_point;
937 	return __time_point(__rhs.time_since_epoch() + __lhs);
938       }
939 
940     /// Adjust a time point backwards by the given duration.
941     template<typename _Clock, typename _Dur1,
942 	     typename _Rep2, typename _Period2>
943       constexpr time_point<_Clock,
944 	typename common_type<_Dur1, duration<_Rep2, _Period2>>::type>
945       operator-(const time_point<_Clock, _Dur1>& __lhs,
946 		const duration<_Rep2, _Period2>& __rhs)
947       {
948 	typedef duration<_Rep2, _Period2>			__dur2;
949 	typedef typename common_type<_Dur1,__dur2>::type	__ct;
950 	typedef time_point<_Clock, __ct>			__time_point;
951 	return __time_point(__lhs.time_since_epoch() -__rhs);
952       }
953 
954     /// @}
955 
956     /// @relates time_point @{
957 
958     /// The difference between two time points (as a duration)
959     template<typename _Clock, typename _Dur1, typename _Dur2>
960       constexpr typename common_type<_Dur1, _Dur2>::type
961       operator-(const time_point<_Clock, _Dur1>& __lhs,
962 		const time_point<_Clock, _Dur2>& __rhs)
963       { return __lhs.time_since_epoch() - __rhs.time_since_epoch(); }
964 
965     template<typename _Clock, typename _Dur1, typename _Dur2>
966       constexpr bool
967       operator==(const time_point<_Clock, _Dur1>& __lhs,
968 		 const time_point<_Clock, _Dur2>& __rhs)
969       { return __lhs.time_since_epoch() == __rhs.time_since_epoch(); }
970 
971 #if __cpp_lib_three_way_comparison
972     template<typename _Clock, typename _Dur1,
973 	     three_way_comparable_with<_Dur1> _Dur2>
974       constexpr auto
975       operator<=>(const time_point<_Clock, _Dur1>& __lhs,
976 		  const time_point<_Clock, _Dur2>& __rhs)
977       { return __lhs.time_since_epoch() <=> __rhs.time_since_epoch(); }
978 #else
979     template<typename _Clock, typename _Dur1, typename _Dur2>
980       constexpr bool
981       operator!=(const time_point<_Clock, _Dur1>& __lhs,
982 		 const time_point<_Clock, _Dur2>& __rhs)
983       { return !(__lhs == __rhs); }
984 #endif
985 
986     template<typename _Clock, typename _Dur1, typename _Dur2>
987       constexpr bool
988       operator<(const time_point<_Clock, _Dur1>& __lhs,
989 		const time_point<_Clock, _Dur2>& __rhs)
990       { return  __lhs.time_since_epoch() < __rhs.time_since_epoch(); }
991 
992     template<typename _Clock, typename _Dur1, typename _Dur2>
993       constexpr bool
994       operator<=(const time_point<_Clock, _Dur1>& __lhs,
995 		 const time_point<_Clock, _Dur2>& __rhs)
996       { return !(__rhs < __lhs); }
997 
998     template<typename _Clock, typename _Dur1, typename _Dur2>
999       constexpr bool
1000       operator>(const time_point<_Clock, _Dur1>& __lhs,
1001 		const time_point<_Clock, _Dur2>& __rhs)
1002       { return __rhs < __lhs; }
1003 
1004     template<typename _Clock, typename _Dur1, typename _Dur2>
1005       constexpr bool
1006       operator>=(const time_point<_Clock, _Dur1>& __lhs,
1007 		 const time_point<_Clock, _Dur2>& __rhs)
1008       { return !(__lhs < __rhs); }
1009 
1010     /// @}
1011 
1012     // Clocks.
1013 
1014     // Why nanosecond resolution as the default?
1015     // Why have std::system_clock always count in the highest
1016     // resolution (ie nanoseconds), even if on some OSes the low 3
1017     // or 9 decimal digits will be always zero? This allows later
1018     // implementations to change the system_clock::now()
1019     // implementation any time to provide better resolution without
1020     // changing function signature or units.
1021 
1022     // To support the (forward) evolution of the library's defined
1023     // clocks, wrap inside inline namespace so that the current
1024     // defintions of system_clock, steady_clock, and
1025     // high_resolution_clock types are uniquely mangled. This way, new
1026     // code can use the latests clocks, while the library can contain
1027     // compatibility definitions for previous versions.  At some
1028     // point, when these clocks settle down, the inlined namespaces
1029     // can be removed.  XXX GLIBCXX_ABI Deprecated
1030     inline namespace _V2 {
1031 
1032     /**
1033      *  @brief System clock.
1034      *
1035      *  Time returned represents wall time from the system-wide clock.
1036      *  @ingroup chrono
1037     */
1038     struct system_clock
1039     {
1040       typedef chrono::nanoseconds				duration;
1041       typedef duration::rep					rep;
1042       typedef duration::period					period;
1043       typedef chrono::time_point<system_clock, duration> 	time_point;
1044 
1045       static_assert(system_clock::duration::min()
1046 		    < system_clock::duration::zero(),
1047 		    "a clock's minimum duration cannot be less than its epoch");
1048 
1049       static constexpr bool is_steady = false;
1050 
1051       static time_point
1052       now() noexcept;
1053 
1054       // Map to C API
1055       static std::time_t
1056       to_time_t(const time_point& __t) noexcept
1057       {
1058 	return std::time_t(duration_cast<chrono::seconds>
1059 			   (__t.time_since_epoch()).count());
1060       }
1061 
1062       static time_point
1063       from_time_t(std::time_t __t) noexcept
1064       {
1065 	typedef chrono::time_point<system_clock, seconds>	__from;
1066 	return time_point_cast<system_clock::duration>
1067 	       (__from(chrono::seconds(__t)));
1068       }
1069     };
1070 
1071 
1072     /**
1073      *  @brief Monotonic clock
1074      *
1075      *  Time returned has the property of only increasing at a uniform rate.
1076      *  @ingroup chrono
1077     */
1078     struct steady_clock
1079     {
1080       typedef chrono::nanoseconds				duration;
1081       typedef duration::rep					rep;
1082       typedef duration::period					period;
1083       typedef chrono::time_point<steady_clock, duration>	time_point;
1084 
1085       static constexpr bool is_steady = true;
1086 
1087       static time_point
1088       now() noexcept;
1089     };
1090 
1091 
1092     /**
1093      *  @brief Highest-resolution clock
1094      *
1095      *  This is the clock "with the shortest tick period." Alias to
1096      *  std::system_clock until higher-than-nanosecond definitions
1097      *  become feasible.
1098      *  @ingroup chrono
1099     */
1100     using high_resolution_clock = system_clock;
1101 
1102     } // end inline namespace _V2
1103 
1104 #if __cplusplus > 201703L
1105     template<typename _Duration>
1106       using sys_time = time_point<system_clock, _Duration>;
1107     using sys_seconds = sys_time<seconds>;
1108     using sys_days = sys_time<days>;
1109 
1110     using file_clock = ::std::filesystem::__file_clock;
1111 
1112     template<typename _Duration>
1113       using file_time = time_point<file_clock, _Duration>;
1114 
1115     template<> struct is_clock<system_clock> : true_type { };
1116     template<> struct is_clock<steady_clock> : true_type { };
1117     template<> struct is_clock<file_clock> : true_type { };
1118 
1119     template<> inline constexpr bool is_clock_v<system_clock> = true;
1120     template<> inline constexpr bool is_clock_v<steady_clock> = true;
1121     template<> inline constexpr bool is_clock_v<file_clock> = true;
1122 
1123     struct local_t { };
1124     template<typename _Duration>
1125       using local_time = time_point<local_t, _Duration>;
1126     using local_seconds = local_time<seconds>;
1127     using local_days = local_time<days>;
1128 #endif // C++20
1129 
1130     /// @}
1131   } // namespace chrono
1132 
1133 #if __cplusplus > 201103L
1134 
1135 #define __cpp_lib_chrono_udls 201304
1136 
1137   inline namespace literals
1138   {
1139   /** ISO C++ 2014  namespace for suffixes for duration literals.
1140    *
1141    * These suffixes can be used to create `chrono::duration` values with
1142    * tick periods of hours, minutes, seconds, milliseconds, microseconds
1143    * or nanoseconds. For example, `std::chrono::seconds(5)` can be written
1144    * as `5s` after making the suffix visible in the current scope.
1145    * The suffixes can be made visible by a using-directive or
1146    * using-declaration such as:
1147    *  - `using namespace std::chrono_literals;`
1148    *  - `using namespace std::literals;`
1149    *  - `using namespace std::chrono;`
1150    *  - `using namespace std;`
1151    *  - `using std::chrono_literals::operator""s;`
1152    *
1153    * The result of these suffixes on an integer literal is one of the
1154    * standard typedefs such as `std::chrono::hours`.
1155    * The result on a floating-point literal is a duration type with the
1156    * specified tick period and an unspecified floating-point representation,
1157    * for example `1.5e2ms` might be equivalent to
1158    * `chrono::duration<long double, chrono::milli>(1.5e2)`.
1159    *
1160    * @ingroup chrono
1161    */
1162   inline namespace chrono_literals
1163   {
1164 #pragma GCC diagnostic push
1165 #pragma GCC diagnostic ignored "-Wliteral-suffix"
1166     /// @cond undocumented
1167     template<typename _Dur, char... _Digits>
1168       constexpr _Dur __check_overflow()
1169       {
1170 	using _Val = __parse_int::_Parse_int<_Digits...>;
1171 	constexpr typename _Dur::rep __repval = _Val::value;
1172 	static_assert(__repval >= 0 && __repval == _Val::value,
1173 		      "literal value cannot be represented by duration type");
1174 	return _Dur(__repval);
1175       }
1176     /// @endcond
1177 
1178     /// Literal suffix for durations representing non-integer hours
1179     constexpr chrono::duration<long double, ratio<3600,1>>
1180     operator""h(long double __hours)
1181     { return chrono::duration<long double, ratio<3600,1>>{__hours}; }
1182 
1183     /// Literal suffix for durations of type `std::chrono::hours`
1184     template <char... _Digits>
1185       constexpr chrono::hours
1186       operator""h()
1187       { return __check_overflow<chrono::hours, _Digits...>(); }
1188 
1189     /// Literal suffix for durations representing non-integer minutes
1190     constexpr chrono::duration<long double, ratio<60,1>>
1191     operator""min(long double __mins)
1192     { return chrono::duration<long double, ratio<60,1>>{__mins}; }
1193 
1194     /// Literal suffix for durations of type `std::chrono::minutes`
1195     template <char... _Digits>
1196       constexpr chrono::minutes
1197       operator""min()
1198       { return __check_overflow<chrono::minutes, _Digits...>(); }
1199 
1200     /// Literal suffix for durations representing non-integer seconds
1201     constexpr chrono::duration<long double>
1202     operator""s(long double __secs)
1203     { return chrono::duration<long double>{__secs}; }
1204 
1205     /// Literal suffix for durations of type `std::chrono::seconds`
1206     template <char... _Digits>
1207       constexpr chrono::seconds
1208       operator""s()
1209       { return __check_overflow<chrono::seconds, _Digits...>(); }
1210 
1211     /// Literal suffix for durations representing non-integer milliseconds
1212     constexpr chrono::duration<long double, milli>
1213     operator""ms(long double __msecs)
1214     { return chrono::duration<long double, milli>{__msecs}; }
1215 
1216     /// Literal suffix for durations of type `std::chrono::milliseconds`
1217     template <char... _Digits>
1218       constexpr chrono::milliseconds
1219       operator""ms()
1220       { return __check_overflow<chrono::milliseconds, _Digits...>(); }
1221 
1222     /// Literal suffix for durations representing non-integer microseconds
1223     constexpr chrono::duration<long double, micro>
1224     operator""us(long double __usecs)
1225     { return chrono::duration<long double, micro>{__usecs}; }
1226 
1227     /// Literal suffix for durations of type `std::chrono::microseconds`
1228     template <char... _Digits>
1229       constexpr chrono::microseconds
1230       operator""us()
1231       { return __check_overflow<chrono::microseconds, _Digits...>(); }
1232 
1233     /// Literal suffix for durations representing non-integer nanoseconds
1234     constexpr chrono::duration<long double, nano>
1235     operator""ns(long double __nsecs)
1236     { return chrono::duration<long double, nano>{__nsecs}; }
1237 
1238     /// Literal suffix for durations of type `std::chrono::nanoseconds`
1239     template <char... _Digits>
1240       constexpr chrono::nanoseconds
1241       operator""ns()
1242       { return __check_overflow<chrono::nanoseconds, _Digits...>(); }
1243 
1244 #pragma GCC diagnostic pop
1245   } // inline namespace chrono_literals
1246   } // inline namespace literals
1247 
1248   namespace chrono
1249   {
1250     using namespace literals::chrono_literals;
1251   } // namespace chrono
1252 
1253 #if __cplusplus >= 201703L
1254   namespace filesystem
1255   {
1256     struct __file_clock
1257     {
1258       using duration                  = chrono::nanoseconds;
1259       using rep                       = duration::rep;
1260       using period                    = duration::period;
1261       using time_point                = chrono::time_point<__file_clock>;
1262       static constexpr bool is_steady = false;
1263 
1264       static time_point
1265       now() noexcept
1266       { return _S_from_sys(chrono::system_clock::now()); }
1267 
1268 #if __cplusplus > 201703L
1269       template<typename _Dur>
1270 	static
1271 	chrono::file_time<_Dur>
1272 	from_sys(const chrono::sys_time<_Dur>& __t) noexcept
1273 	{ return _S_from_sys(__t); }
1274 
1275       // For internal use only
1276       template<typename _Dur>
1277 	static
1278 	chrono::sys_time<_Dur>
1279 	to_sys(const chrono::file_time<_Dur>& __t) noexcept
1280 	{ return _S_to_sys(__t); }
1281 #endif // C++20
1282 
1283     private:
1284       using __sys_clock = chrono::system_clock;
1285 
1286       // This clock's (unspecified) epoch is 2174-01-01 00:00:00 UTC.
1287       // A signed 64-bit duration with nanosecond resolution gives roughly
1288       // +/- 292 years, which covers the 1901-2446 date range for ext4.
1289       static constexpr chrono::seconds _S_epoch_diff{6437664000};
1290 
1291     protected:
1292       // For internal use only
1293       template<typename _Dur>
1294 	static
1295 	chrono::time_point<__file_clock, _Dur>
1296 	_S_from_sys(const chrono::time_point<__sys_clock, _Dur>& __t) noexcept
1297 	{
1298 	  using __file_time = chrono::time_point<__file_clock, _Dur>;
1299 	  return __file_time{__t.time_since_epoch()} - _S_epoch_diff;
1300 	}
1301 
1302       // For internal use only
1303       template<typename _Dur>
1304 	static
1305 	chrono::time_point<__sys_clock, _Dur>
1306 	_S_to_sys(const chrono::time_point<__file_clock, _Dur>& __t) noexcept
1307 	{
1308 	  using __sys_time = chrono::time_point<__sys_clock, _Dur>;
1309 	  return __sys_time{__t.time_since_epoch()} + _S_epoch_diff;
1310 	}
1311     };
1312   } // namespace filesystem
1313 #endif // C++17
1314 #endif // C++14
1315 
1316 _GLIBCXX_END_NAMESPACE_VERSION
1317 } // namespace std
1318 
1319 #endif // C++11
1320 
1321 #endif //_GLIBCXX_CHRONO
1322