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* [gcc r11-3164] libstdc++: Fix chrono::__detail::ceil to work with C++11
@ 2020-09-11 18:59 Jonathan Wakely
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From: Jonathan Wakely @ 2020-09-11 18:59 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:53ad6b1979f4bd7121e977c4a44151b14d8a0147
commit r11-3164-g53ad6b1979f4bd7121e977c4a44151b14d8a0147
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Fri Sep 11 19:59:11 2020 +0100
libstdc++: Fix chrono::__detail::ceil to work with C++11
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.
Diff:
---
libstdc++-v3/include/std/chrono | 45 +++++++++++++++++++++++++++--------------
1 file changed, 30 insertions(+), 15 deletions(-)
diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono
index 893d1f6b2c9..7539d7184ea 100644
--- a/libstdc++-v3/include/std/chrono
+++ b/libstdc++-v3/include/std/chrono
@@ -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
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