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libstdc++: Fix chrono::__detail::ceil to work with C++11

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In C++11 constexpr functions can only have a return statement, so we
need to fix __detail::ceil to make it valid in C++11. This can be done
by moving the comparison and increment into a new function, __ceil_impl,
and calling that with the result of the duration_cast.

This would mean the standard C++17 std::chrono::ceil function would make
two further calls, which would add too much overhead when not inlined.
For C++17 and later use a using-declaration to add chrono::ceil to
namespace __detail. For C++11 and C++14 define chrono::__detail::__ceil
as a C++11-compatible constexpr function template.

libstdc++-v3/ChangeLog:

	* include/std/chrono [C++17] (chrono::__detail::ceil): Add
	using declaration to make chrono::ceil available for internal
	use with a consistent name.
	(chrono::__detail::__ceil_impl): New function template.
	(chrono::__detail::ceil): Use __ceil_impl to compare and
	increment the value. Remove SFINAE constraint.
This commit is contained in:
Jonathan Wakely 2020-09-11 19:59:11 +01:00
parent 40e99ed5f4
commit 53ad6b1979
1 changed files with 30 additions and 15 deletions
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45
libstdc++-v3/include/std/chrono
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@ -329,20 +329,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#endif
#endif // C++20
// We want to use ceil even when compiling for earlier standards versions
namespace __detail
{
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;
}
}
#if __cplusplus >= 201703L
# define __cpp_lib_chrono 201611
@ -360,7 +346,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr __enable_if_is_duration<_ToDur>
ceil(const duration<_Rep, _Period>& __d)
{
return __detail::ceil<_ToDur>(__d);
auto __to = chrono::duration_cast<_ToDur>(__d);
if (__to < __d)
return __to + _ToDur{1};
return __to;
}
template <typename _ToDur, typename _Rep, typename _Period>
@ -394,6 +383,32 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
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