On Friday 11 September 2020 at 19:59:36 +0100, Jonathan Wakely wrote: > commit 53ad6b1979f4bd7121e977c4a44151b14d8a0147 > Author: Jonathan Wakely <jwak...@redhat.com> > Date: Fri Sep 11 19:59:11 2020 > > 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.
This change introduces a new implementation of ceil that, as far as I can tell, has no tests. A patch is attached to add the equivalent of the existing chrono::ceil tests for chrono::__detail::ceil. The tests fail to compile if I run them without 53ad6b1979f4bd7121e977c4a44151b14d8a0147 as expected due to the previous non-C++11-compliant implementation. Mike.
>From b9dffbf4f1bc05a887269ea95a3b86d5a611e720 Mon Sep 17 00:00:00 2001 From: Mike Crowe <m...@mcrowe.com> Date: Wed, 16 Sep 2020 15:31:28 +0100 Subject: [PATCH 1/2] libstdc++: Test C++11 implementation of std::chrono::__detail::ceil Commit 53ad6b1979f4bd7121e977c4a44151b14d8a0147 split the implementation of std::chrono::__detail::ceil so that when compiling for C++17 and later std::chrono::ceil is used but when compiling for earlier versions a separate implementation is used to comply with C++11's limited constexpr rules. Let's run the equivalent of the existing std::chrono::ceil test cases on std::chrono::__detail::ceil too to make sure that it doesn't get broken. libstdc++-v3/ChangeLog: * testsuite/20_util/duration_cast/rounding_c++11.cc: Copy rounding.cc and alter to support compilation for C++11 and to test std::chrono::__detail::ceil. --- .../20_util/duration_cast/rounding_c++11.cc | 43 +++++++++++++++++++ 1 file changed, 43 insertions(+) create mode 100644 libstdc++-v3/testsuite/20_util/duration_cast/rounding_c++11.cc diff --git a/libstdc++-v3/testsuite/20_util/duration_cast/rounding_c++11.cc b/libstdc++-v3/testsuite/20_util/duration_cast/rounding_c++11.cc new file mode 100644 index 00000000000..f10d27fd082 --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/duration_cast/rounding_c++11.cc @@ -0,0 +1,43 @@ +// Copyright (C) 2016-2020 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the +// terms of the GNU General Public License as published by the +// Free Software Foundation; either version 3, or (at your option) +// any later version. + +// This library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// <http://www.gnu.org/licenses/>. + +// { dg-options "-std=gnu++11" } +// { dg-do compile { target c++11 } } + +#include <chrono> + +using std::chrono::seconds; +using std::chrono::milliseconds; + +using fp_seconds = std::chrono::duration<float>; + +static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(1000)) + == seconds(1) ); +static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(1001)) + == seconds(2) ); +static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(1500)) + == seconds(2) ); +static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(1999)) + == seconds(2) ); +static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(2000)) + == seconds(2) ); +static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(2001)) + == seconds(3) ); +static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(2500)) + == seconds(3) ); +static_assert( std::chrono::__detail::ceil<fp_seconds>(milliseconds(500)) + == fp_seconds{0.5f} ); -- 2.28.0