On 28/10/20 11:21 -0400, Patrick Palka via Libstdc++ wrote:
On Wed, 28 Oct 2020, Patrick Palka wrote:The conversion function year_month_weekday::operator sys_days computes the number of days to offset from the first weekday of the month with: days{(index()-1)*7} ^~~~~~~~~~~~~ type 'unsigned' We'd like 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 long instead yields a large positive quantity. 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 that we do the right thing when index() == 5. Tested on x86_64-pc-linux-gnu, does this look OK for trunk? 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. --- libstdc++-v3/include/std/chrono | 3 +- .../std/time/year_month_weekday/3.cc | 66 +++++++++++++++++++ 2 files changed, 68 insertions(+), 1 deletion(-) create mode 100644 libstdc++-v3/testsuite/std/time/year_month_weekday/3.cc diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono index 7539d7184ea..7c35b78fe59 100644 --- a/libstdc++-v3/include/std/chrono +++ b/libstdc++-v3/include/std/chrono @@ -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{((int)index()-1)*7});On second thought, for consistency with the rest of the header, I guess we should use a functional cast instead of a C-style cast here:
Or static_cast<int>(index()) :-) Any of those options is OK.
