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libstdc++: Fix formatting of negative chrono::hh_mm_ss

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When formatting with an empty chrono spec ("{}") two minus signs were
being added to hh_mm_ss values. This is because the __is_neg flag was
checked to add one explicitly, and then the ostream operator added
another one.

We should only check the __is_neg flag for durations, because those are
the only types which are modified to be non-negative before calling
_M_format. We don't change hh_mm_ss values to be negative, because that
would require performing arithmetic on the hh_mm_ss members to sum them,
and then again to construct a new hh_mm_ss object with the positive
value.  Instead, we can just be careful about using the __is_neg flag
correctly.

To fix the bug, _M_format_to_ostream no longer checks the __is_neg flag
for non-durations, and _M_format doesn't set it for hh_mm_ss until after
the call to _M_format_to_ostream. We can also avoid setting it for types
that it doesn't apply to, by making the __print_sign lambda only inspect
it for duration and hh_mm_ss types.

libstdc++-v3/ChangeLog:

	* include/bits/chrono_io.h (__formatter_chrono::_M_format):
	Do not set __is_neg for hh_mm_ss before calling
	_M_format_to_ostream. Change __print_sign lambda to only check
	__is_neg for durations and hh_mm_ss types.
	(__formatter_chrono::_M_format_to_ostream): Only check __is_neg
	for duration types.
	* testsuite/std/time/hh_mm_ss/io.cc: Check negative values.
This commit is contained in:
Jonathan Wakely 2023-07-19 14:42:51 +01:00
parent 86b36e9f7e
commit 344f413220
2 changed files with 19 additions and 12 deletions
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27
libstdc++-v3/include/bits/chrono_io.h
View file

@ -486,11 +486,6 @@ namespace __format
_M_format(const _Tp& __t, _FormatContext& __fc,
bool __is_neg = false) const
{
if constexpr (__is_specialization_of<_Tp, chrono::hh_mm_ss>)
__is_neg = __t.is_negative();
else if constexpr (!chrono::__is_duration_v<_Tp>)
__is_neg = false;
auto __first = _M_spec._M_chrono_specs.begin();
const auto __last = _M_spec._M_chrono_specs.end();
if (__first == __last)
@ -513,12 +508,19 @@ namespace __format
else
__out = __sink.out();
// formatter<duration> passes the correct value of __is_neg
// for durations but for hh_mm_ss we decide it here.
if constexpr (__is_specialization_of<_Tp, chrono::hh_mm_ss>)
__is_neg = __t.is_negative();
auto __print_sign = [&__is_neg, &__out] {
if (__is_neg)
{
*__out++ = _S_plus_minus[1];
__is_neg = false;
}
if constexpr (chrono::__is_duration_v<_Tp>
|| __is_specialization_of<_Tp, chrono::hh_mm_ss>)
if (__is_neg)
{
*__out++ = _S_plus_minus[1];
__is_neg = false;
}
return std::move(__out);
};
@ -708,8 +710,9 @@ namespace __format
__os << __t._M_date << ' ' << __t._M_time;
else
{
if (__is_neg) [[unlikely]]
__os << _S_plus_minus[1];
if constexpr (chrono::__is_duration_v<_Tp>)
if (__is_neg) [[unlikely]]
__os << _S_plus_minus[1];
__os << __t;
}

4
libstdc++-v3/testsuite/std/time/hh_mm_ss/io.cc
View file

@ -47,9 +47,13 @@ test_format()
auto s = std::format("{}", hh_mm_ss{1h + 23min + 45s});
VERIFY( s == "01:23:45" );
s = std::format("{}", hh_mm_ss{-42min});
VERIFY( s == "-00:42:00" );
auto ws = std::format(L"{}", hh_mm_ss{1h + 23min + 45s});
VERIFY( ws == L"01:23:45" );
ws = std::format(L"{}", hh_mm_ss{-42min});
VERIFY( ws == L"-00:42:00" );
// Locale-specific formats:
auto loc = std::locale::classic();