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| author | Jonathan Wakely <jwakely@redhat.com> | 2024-09-18 17:20:29 +0100 |
|---|---|---|
| committer | Jonathan Wakely <redi@gcc.gnu.org> | 2024-09-22 17:45:06 +0100 |
| commit | 482e651f5750e4648ade90e32ed45b094538e7f8 (patch) | |
| tree | aa1734619b465e73ef54ad98f40bd862fd00bc8f | |
| parent | b6463161c3cd0b1f764697290d9569c7153b8a5b (diff) | |
| download | gcc-482e651f5750e4648ade90e32ed45b094538e7f8.zip gcc-482e651f5750e4648ade90e32ed45b094538e7f8.tar.gz gcc-482e651f5750e4648ade90e32ed45b094538e7f8.tar.bz2 | |
libstdc++: Fix formatting of most negative chrono::duration [PR116755]
When formatting chrono::duration<signed-integer-type, P>::min() we were
causing undefined behaviour by trying to form the negative of the most
negative value. If we convert negative durations with integer rep to the
corresponding unsigned integer rep then we can safely represent all
values.
libstdc++-v3/ChangeLog:
PR libstdc++/116755
* include/bits/chrono_io.h (formatter<duration<R,P>>::format):
Cast negative integral durations to unsigned rep.
* testsuite/20_util/duration/io.cc: Test the most negative
integer durations.
| -rw-r--r-- | libstdc++-v3/include/bits/chrono_io.h | 16 | ||||
| -rw-r--r-- | libstdc++-v3/testsuite/20_util/duration/io.cc | 8 |
2 files changed, 22 insertions, 2 deletions
diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h index 0e4d23c..c7d2c98 100644 --- a/libstdc++-v3/include/bits/chrono_io.h +++ b/libstdc++-v3/include/bits/chrono_io.h @@ -1720,8 +1720,20 @@ namespace __format basic_format_context<_Out, _CharT>& __fc) const { if constexpr (numeric_limits<_Rep>::is_signed) - if (__d < __d.zero()) - return _M_f._M_format(-__d, __fc, true); + if (__d < __d.zero()) [[unlikely]] + { + if constexpr (is_integral_v<_Rep>) + { + // -d is undefined for the most negative integer. + // Convert duration to corresponding unsigned rep. + using _URep = make_unsigned_t<_Rep>; + auto __ucnt = -static_cast<_URep>(__d.count()); + auto __ud = chrono::duration<_URep, _Period>(__ucnt); + return _M_f._M_format(__ud, __fc, true); + } + else + return _M_f._M_format(-__d, __fc, true); + } return _M_f._M_format(__d, __fc, false); } diff --git a/libstdc++-v3/testsuite/20_util/duration/io.cc b/libstdc++-v3/testsuite/20_util/duration/io.cc index 6b00689..57020f4 100644 --- a/libstdc++-v3/testsuite/20_util/duration/io.cc +++ b/libstdc++-v3/testsuite/20_util/duration/io.cc @@ -106,6 +106,14 @@ test_format() VERIFY( s == "500ms" ); s = std::format("{:%Q %q}", u); VERIFY( s == "500 ms" ); + + // PR libstdc++/116755 extra minus sign for most negative value + auto minsec = std::chrono::seconds::min(); + s = std::format("{}", minsec); + auto expected = std::format("{}s", minsec.count()); + VERIFY( s == expected ); + s = std::format("{:%Q%q}", minsec); + VERIFY( s == expected ); } void |