From 82030d51017323c5706d58d8c8626324ece007e4 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Thu, 27 Aug 2020 22:36:03 +0100 Subject: libstdc++: Make std::chrono::duration use reduced ratio for period This implements the changes from P0548 "common_type and duration". That was a change for C++17, but as it corrects some issues introduced by DRs I'm also treating it as a DR and changing it for all modes from C++11 up. The main change is that duration::period no longer denotes P, but rather P::type, the reduced ratio. The unary operator+ and operator- members of duration should now return a duration using that reduced ratio. The requirement that common_type::type is the same type as common_type::type (rather than simply T) was already implemented for PR 89102. The standard says that duration::operator+() and duration::operator-() should return common_type_t, but that seems unnecessarily expensive to compute. This change just uses duration which is the same type, so we don't need to instantiate common_type. As an optimization, this also adds partial specializations of common_type for two durations of the same type, a single duration, two time_points of the same type, and a single time_point. These specializations avoid instantiating other specializations of common_type and one or both of __duration_common_type or __timepoint_common_type for the cases where the answer is trivial to obtain. libstdc++-v3/ChangeLog: * include/std/chrono (__duration_common_type): Ensure the reduced ratio is used. Remove unused partial specialization using __failure_type. (common_type): Pass reduced ratios to __duration_common_type. Add partial specializations for simple cases involving a single duration or time_point type. (duration::period): Use reduced ratio. (duration::operator+(), duration::operator-()): Return duration type using the reduced ratio. * testsuite/20_util/duration/requirements/typedefs_neg2.cc: Adjust expected errors. * testsuite/20_util/duration/requirements/reduced_period.cc: New test. --- libstdc++-v3/include/std/chrono | 45 ++++++++++++++++++++++++++++++++--------- 1 file changed, 35 insertions(+), 10 deletions(-) (limited to 'libstdc++-v3/include/std/chrono') diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono index 9fc8f56..fb25184 100644 --- a/libstdc++-v3/include/std/chrono +++ b/libstdc++-v3/include/std/chrono @@ -94,13 +94,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION (_Period1::den / __gcd_den::value) * _Period2::den>; public: - using type = chrono::duration<__cr, __r>; + using type = chrono::duration<__cr, typename __r::type>; }; - template - struct __duration_common_type<__failure_type, _Period1, _Period2> - { typedef __failure_type type; }; - /// @endcond /// Specialization of common_type for chrono::duration types. @@ -108,9 +104,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION template struct common_type, chrono::duration<_Rep2, _Period2>> - : __duration_common_type, _Period1, _Period2> + : __duration_common_type, + typename _Period1::type, + typename _Period2::type> { }; + /// Specialization of common_type for two identical chrono::duration types. + /// @relates duration + template + struct common_type, + chrono::duration<_Rep, _Period>> + { using type = chrono::duration<_Rep, typename _Period::type>; }; + + /// Specialization of common_type for one chrono::duration type. + /// @relates duration + template + struct common_type> + { using type = chrono::duration<_Rep, typename _Period::type>; }; + // 20.11.4.3 specialization of common_type (for time_point, sfinae-friendly) /// @cond undocumented @@ -135,6 +146,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION : __timepoint_common_type, _Clock> { }; + /// Specialization of common_type for two identical chrono::time_point types. + /// @relates time_point + template + struct common_type, + chrono::time_point<_Clock, _Duration>> + { using type = chrono::time_point<_Clock, _Duration>; }; + + /// Specialization of common_type for one chrono::time_point type. + /// @relates time_point + template + struct common_type> + { using type = chrono::time_point<_Clock, _Duration>; }; + // @} group chrono namespace chrono @@ -401,8 +425,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION public: - typedef _Rep rep; - typedef _Period period; + using rep = _Rep; + using period = typename _Period::type; static_assert(!__is_duration<_Rep>::value, "rep cannot be a duration"); static_assert(__is_ratio<_Period>::value, @@ -438,11 +462,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { return __r; } // 20.11.5.3 arithmetic - constexpr duration + + constexpr duration operator+() const { return *this; } - constexpr duration + constexpr duration operator-() const { return duration(-__r); } -- cgit v1.1