FreeChainXenon/gcc
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

libstdc++: Fix arithmetic bug in year_month_weekday conversion [PR96713]

Browse source 
The conversion function year_month_weekday::operator sys_days computes
the offset in days from the first weekday of the month with:

 days{(index()-1)*7}
      ^~~~~~~~~~~~~  type 'unsigned'

We want the above to yield -7d when index() is 0u, but our 'days' alias
is based on long instead of int, so the conversion from unsigned to the
underlying type of 'days' instead yields a large positive value.

This patch fixes this by casting the result of index() to int so that
the initializer is sign-extended in the conversion to long.

The added testcase also verifies we do the right thing when index() == 5.

libstdc++-v3/ChangeLog:

	PR libstdc++/96713
	* include/std/chrono (year_month_weekday::operator sys_days):
	Cast the result of index() to int so that the initializer for
	days{} is sign-extended when it's converted to the underlying
	type.
	* testsuite/std/time/year_month_weekday/3.cc: New test.
This commit is contained in:
Patrick Palka 2020-10-28 12:28:08 -04:00
parent f4af2dde57
commit 8572edc828
2 changed files with 67 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

3
libstdc++-v3/include/std/chrono
View file

@ -2719,7 +2719,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
operator sys_days() const noexcept
{
auto __d = sys_days{year() / month() / 1};
return __d + (weekday() - chrono::weekday(__d) + days{(index()-1)*7});
return __d + (weekday() - chrono::weekday(__d)
+ days{(static_cast<int>(index())-1)*7});
}
explicit constexpr

65
libstdc++-v3/testsuite/std/time/year_month_weekday/3.cc Normal file
View file

@ -0,0 +1,65 @@
// { dg-options "-std=gnu++2a" }
// { dg-do compile { target c++2a } }
// Copyright (C) 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/>.
// PR libstdc++/97613
// Test year_month_weekday to sys_days conversion for extreme values of index().
#include <chrono>
void
test01()
{
using namespace std::chrono;
using ymd = year_month_day;
static_assert(ymd{sys_days{2020y/January/Sunday[0]}} == 2019y/December/29);
static_assert(ymd{sys_days{2020y/January/Monday[0]}} == 2019y/December/30);
static_assert(ymd{sys_days{2020y/January/Tuesday[0]}} == 2019y/December/31);
static_assert(ymd{sys_days{2020y/January/Wednesday[0]}} == 2019y/December/25);
static_assert(ymd{sys_days{2020y/January/Thursday[0]}} == 2019y/December/26);
static_assert(ymd{sys_days{2020y/January/Friday[0]}} == 2019y/December/27);
static_assert(ymd{sys_days{2020y/January/Saturday[0]}} == 2019y/December/28);
static_assert((2020y).is_leap());
static_assert(ymd{sys_days{2020y/March/Sunday[0]}} == 2020y/February/23);
static_assert(ymd{sys_days{2020y/March/Monday[0]}} == 2020y/February/24);
static_assert(ymd{sys_days{2020y/March/Tuesday[0]}} == 2020y/February/25);
static_assert(ymd{sys_days{2020y/March/Wednesday[0]}} == 2020y/February/26);
static_assert(ymd{sys_days{2020y/March/Thursday[0]}} == 2020y/February/27);
static_assert(ymd{sys_days{2020y/March/Friday[0]}} == 2020y/February/28);
static_assert(ymd{sys_days{2020y/March/Saturday[0]}} == 2020y/February/29);
static_assert(!(2019y).is_leap());
static_assert(ymd{sys_days{2019y/March/Sunday[0]}} == 2019y/February/24);
static_assert(ymd{sys_days{2019y/March/Monday[0]}} == 2019y/February/25);
static_assert(ymd{sys_days{2019y/March/Tuesday[0]}} == 2019y/February/26);
static_assert(ymd{sys_days{2019y/March/Wednesday[0]}} == 2019y/February/27);
static_assert(ymd{sys_days{2019y/March/Thursday[0]}} == 2019y/February/28);
static_assert(ymd{sys_days{2019y/March/Friday[0]}} == 2019y/February/22);
static_assert(ymd{sys_days{2019y/March/Saturday[0]}} == 2019y/February/23);
static_assert(ymd{sys_days{2020y/December/Sunday[5]}} == 2021y/January/3);
static_assert(ymd{sys_days{2020y/December/Monday[5]}} == 2021y/January/4);
static_assert(ymd{sys_days{2020y/December/Tuesday[5]}} == 2020y/December/29);
static_assert(ymd{sys_days{2020y/December/Wednesday[5]}} == 2020y/December/30);
static_assert(ymd{sys_days{2020y/December/Thursday[5]}} == 2020y/December/31);
static_assert(ymd{sys_days{2020y/December/Friday[5]}} == 2021y/January/1);
static_assert(ymd{sys_days{2020y/December/Saturday[5]}} == 2021y/January/2);
}