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libstdc++: Define and use variable templates in <chrono>

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Thi defines a variable template for the internal __is_duration helper
trait, defines a new __is_time_point_v variable template (to be used in
a subsequent commit), and adds explicit specializations of the standard
chrono::treat_as_floating_point trait for common types.

A fast path is added to chrono::duration_cast for the no-op case where
no conversion is needed.

Finally, some SFINAE constraints are simplified by using the
__enable_if_t alias, or by using variable templates.

libstdc++-v3/ChangeLog:

	* include/bits/chrono.h (__is_duration_v, __is_time_point_v):
	New variable templates.
	(duration_cast): Add simplified definition for noconv case.
	(treat_as_floating_point_v): Add explicit specializations.
	(duration::operator%=, floor, ceil, round): Simplify SFINAE
	constraints.
This commit is contained in:
Jonathan Wakely 2022-12-22 00:23:19 +00:00
parent ec8f914f57
commit d2d3826cd4
1 changed files with 45 additions and 17 deletions
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62
libstdc++-v3/include/bits/chrono.h
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@ -244,6 +244,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
using __disable_if_is_duration
= typename enable_if<!__is_duration<_Tp>::value, _Tp>::type;
#if __cpp_variable_templates
template<typename _Tp>
inline constexpr bool __is_duration_v = false;
template<typename _Rep, typename _Period>
inline constexpr bool __is_duration_v<duration<_Rep, _Period>> = true;
template<typename _Tp>
inline constexpr bool __is_time_point_v = false;
template<typename _Clock, typename _Dur>
inline constexpr bool __is_time_point_v<time_point<_Clock, _Dur>> = true;
#endif
/// @endcond
/** Convert a `duration` to type `ToDur`.
@ -261,13 +272,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
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);
#if __cpp_inline_variables && __cpp_if_constexpr
if constexpr (is_same_v<_ToDur, duration<_Rep, _Period>>)
return __d;
else
#endif
{
using __to_period = typename _ToDur::period;
using __to_rep = typename _ToDur::rep;
using __cf = ratio_divide<_Period, __to_period>;
using __cr = typename common_type<__to_rep, _Rep, intmax_t>::type;
using __dc = __duration_cast_impl<_ToDur, __cf, __cr,
__cf::num == 1, __cf::den == 1>;
return __dc::__cast(__d);
}
}
/** Trait indicating whether to treat a type as a floating-point type.
@ -290,6 +308,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template <typename _Rep>
inline constexpr bool treat_as_floating_point_v =
treat_as_floating_point<_Rep>::value;
template<>
inline constexpr bool treat_as_floating_point_v<int> = false;
template<>
inline constexpr bool treat_as_floating_point_v<long> = false;
template<>
inline constexpr bool treat_as_floating_point_v<long long> = false;
template<>
inline constexpr bool treat_as_floating_point_v<float> = true;
template<>
inline constexpr bool treat_as_floating_point_v<double> = true;
template<>
inline constexpr bool treat_as_floating_point_v<long double> = true;
#endif // C++17
#if __cplusplus > 201703L
@ -632,8 +663,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// DR 934.
template<typename _Rep2 = rep>
_GLIBCXX17_CONSTEXPR
typename enable_if<!treat_as_floating_point<_Rep2>::value,
duration&>::type
__enable_if_t<!treat_as_floating_point<_Rep2>::value, duration&>
operator%=(const rep& __rhs)
{
__r %= __rhs;
@ -642,8 +672,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Rep2 = rep>
_GLIBCXX17_CONSTEXPR
typename enable_if<!treat_as_floating_point<_Rep2>::value,
duration&>::type
__enable_if_t<!treat_as_floating_point<_Rep2>::value, duration&>
operator%=(const duration& __d)
{
__r %= __d.count();
@ -1019,7 +1048,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
*/
template<typename _ToDur, typename _Clock, typename _Dur>
[[nodiscard]] constexpr
enable_if_t<__is_duration<_ToDur>::value, time_point<_Clock, _ToDur>>
enable_if_t<__is_duration_v<_ToDur>, time_point<_Clock, _ToDur>>
floor(const time_point<_Clock, _Dur>& __tp)
{
return time_point<_Clock, _ToDur>{
@ -1040,7 +1069,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
*/
template<typename _ToDur, typename _Clock, typename _Dur>
[[nodiscard]] constexpr
enable_if_t<__is_duration<_ToDur>::value, time_point<_Clock, _ToDur>>
enable_if_t<__is_duration_v<_ToDur>, time_point<_Clock, _ToDur>>
ceil(const time_point<_Clock, _Dur>& __tp)
{
return time_point<_Clock, _ToDur>{
@ -1062,10 +1091,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
*/
template<typename _ToDur, typename _Clock, typename _Dur>
[[nodiscard]] constexpr
enable_if_t<
__and_<__is_duration<_ToDur>,
__not_<treat_as_floating_point<typename _ToDur::rep>>>::value,
time_point<_Clock, _ToDur>>
enable_if_t<__is_duration_v<_ToDur>
&& !treat_as_floating_point_v<typename _ToDur::rep>,
time_point<_Clock, _ToDur>>
round(const time_point<_Clock, _Dur>& __tp)
{
return time_point<_Clock, _ToDur>{