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Windows utc_minutes_offset(): Fix historical DST accuracy and improve offset calculation speed (~2.5x) (#3508)

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* New utc offset impl for windows and unit tests

* Update utc_minutes_offset()

* Fix warning

* Fix warning

* Fix timezone tests

* Fix timezone tests

* Update tests/test_pattern_formatter.cpp

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update tests/CMakeLists.txt

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Updated utc_minutes_offset() impl

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
This commit is contained in:
Gabi Melman
2026-01-04 18:01:55 +02:00
committed by GitHub
parent 2670f47d02
commit b656d1ceec
4 changed files with 176 additions and 28 deletions
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38
include/spdlog/details/os-inl.h
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@@ -243,31 +243,29 @@ SPDLOG_INLINE size_t filesize(FILE *f) {
#pragma warning(pop)
#endif
// Return utc offset in minutes or throw spdlog_ex on failure
#if !defined(SPDLOG_NO_TZ_OFFSET)
SPDLOG_INLINE int utc_minutes_offset(const std::tm &tm) {
#ifdef _WIN32
#if _WIN32_WINNT < _WIN32_WINNT_WS08
TIME_ZONE_INFORMATION tzinfo;
auto rv = ::GetTimeZoneInformation(&tzinfo);
#else
DYNAMIC_TIME_ZONE_INFORMATION tzinfo;
auto rv = ::GetDynamicTimeZoneInformation(&tzinfo);
#endif
if (rv == TIME_ZONE_ID_INVALID) throw_spdlog_ex("Failed getting timezone info. ", errno);
int offset = -tzinfo.Bias;
if (tm.tm_isdst) {
offset -= tzinfo.DaylightBias;
} else {
offset -= tzinfo.StandardBias;
// Compare the timestamp as Local (mktime) vs UTC (_mkgmtime) to get the offset.
SPDLOG_INLINE int utc_minutes_offset(const std::tm &tm) {
std::tm local_tm = tm; // copy since mktime might adjust it (normalize dates, set tm_isdst)
std::time_t local_time_t = std::mktime(&local_tm);
if (local_time_t == -1) {
return 0; // fallback
}
return offset;
#else
auto offset_seconds = tm.tm_gmtoff;
std::time_t utc_time_t = _mkgmtime(&local_tm);
if (utc_time_t == -1) {
return 0; // fallback
}
auto offset_seconds = utc_time_t - local_time_t;
return static_cast<int>(offset_seconds / 60);
#endif
}
#else
// On unix simply use tm_gmtoff
SPDLOG_INLINE int utc_minutes_offset(const std::tm &tm) {
return static_cast<int>(tm.tm_gmtoff / 60);
}
#endif // _WIN32
#endif // SPDLOG_NO_TZ_OFFSET
// Return current thread id as size_t