// There's no posix function that does a UTC version of mktime,
// so annoyingly we need to implement this manually..
static inline int64 mktime_utc (const std::tm& t) noexcept
{
return 24 * 3600 * (daysFrom1970 (t.tm_year + 1900, t.tm_mon) + (t.tm_mday - 1))
+ 3600 * t.tm_hour
+ 60 * t.tm_min
+ t.tm_sec;
}
static inline int64 daysFrom1970 (int year, int month) noexcept
{
if (month > 11)
{
year += month / 12;
month %= 12;
}
else if (month < 0)
{
const int numYears = (11 - month) / 12;
year -= numYears;
month += 12 * numYears;
}
return daysFrom1970 (year) + daysFromJan1 (year, month);
}
time_t timegm(tm* t) {
int year = t->tm_year + 1900;
int month = t->tm_mon;
if (month > 11) {
year += month / 12;
month %= 12;
} else if (month < 0) {
int years_diff = (-month + 11) / 12;
year -= years_diff;
month += 12 * years_diff;
}
month++;
int day = t->tm_mday;
int dayOfYear = daysFrom1Jan(year, month, day);
int daysSinceEpoch = daysFrom1970(year) + dayOfYear;
time_t seconds_in_day = 3600 * 24;
time_t result = seconds_in_day * daysSinceEpoch + 3600 * t->tm_hour + 60 * t->tm_min + t->tm_sec;
return result;
}