// Get the DST offset, given a time in UTC
static double getDSTOffset(double ms)
{
// On Mac OS X, the call to localtime (see getDSTOffsetSimple) will return historically accurate
// DST information (e.g. New Zealand did not have DST from 1946 to 1974) however the JavaScript
// standard explicitly dictates that historical information should not be considered when
// determining DST. For this reason we shift away from years that localtime can handle but would
// return historically accurate information.
int year = msToYear(ms);
int equvalentYear = equivalentYearForDST(year);
if (year != equvalentYear) {
int day = dateToDayInYear(equvalentYear, msToMonth(ms), msToDayInMonth(ms));
ms = (day * msPerDay) + msToMilliseconds(ms);
}
return getDSTOffsetSimple(ms / msPerSecond);
}
// Returns combined offset in millisecond (UTC + DST).
LocalTimeOffset calculateLocalTimeOffset(double ms, TimeType inputTimeType)
{
#if HAVE(TM_GMTOFF)
double localToUTCTimeOffset = inputTimeType == LocalTime ? calculateUTCOffset() : 0;
#else
double localToUTCTimeOffset = calculateUTCOffset();
#endif
if (inputTimeType == LocalTime)
ms -= localToUTCTimeOffset;
// On Mac OS X, the call to localtime (see calculateDSTOffset) will return historically accurate
// DST information (e.g. New Zealand did not have DST from 1946 to 1974) however the JavaScript
// standard explicitly dictates that historical information should not be considered when
// determining DST. For this reason we shift away from years that localtime can handle but would
// return historically accurate information.
int year = msToYear(ms);
int equivalentYear = equivalentYearForDST(year);
if (year != equivalentYear) {
bool leapYear = isLeapYear(year);
int dayInYearLocal = dayInYear(ms, year);
int dayInMonth = dayInMonthFromDayInYear(dayInYearLocal, leapYear);
int month = monthFromDayInYear(dayInYearLocal, leapYear);
double day = dateToDaysFrom1970(equivalentYear, month, dayInMonth);
ms = (day * msPerDay) + msToMilliseconds(ms);
}
double localTimeSeconds = ms / msPerSecond;
if (localTimeSeconds > maxUnixTime)
localTimeSeconds = maxUnixTime;
else if (localTimeSeconds < 0) // Go ahead a day to make localtime work (does not work with 0).
localTimeSeconds += secondsPerDay;
// FIXME: time_t has a potential problem in 2038.
time_t localTime = static_cast<time_t>(localTimeSeconds);
#if HAVE(TM_GMTOFF)
tm localTM;
getLocalTime(&localTime, &localTM);
return LocalTimeOffset(localTM.tm_isdst, localTM.tm_gmtoff * msPerSecond);
#else
double dstOffset = calculateDSTOffset(localTime, localToUTCTimeOffset);
return LocalTimeOffset(dstOffset, localToUTCTimeOffset + dstOffset);
#endif
}
// Get the DST offset, given a time in UTC
static double calculateDSTOffset(double ms, double utcOffset)
{
// On Mac OS X, the call to localtime (see calculateDSTOffsetSimple) will return historically accurate
// DST information (e.g. New Zealand did not have DST from 1946 to 1974) however the JavaScript
// standard explicitly dictates that historical information should not be considered when
// determining DST. For this reason we shift away from years that localtime can handle but would
// return historically accurate information.
int year = msToYear(ms);
int equivalentYear = equivalentYearForDST(year);
if (year != equivalentYear) {
bool leapYear = isLeapYear(year);
int dayInYearLocal = dayInYear(ms, year);
int dayInMonth = dayInMonthFromDayInYear(dayInYearLocal, leapYear);
int month = monthFromDayInYear(dayInYearLocal, leapYear);
double day = dateToDaysFrom1970(equivalentYear, month, dayInMonth);
ms = (day * msPerDay) + msToMilliseconds(ms);
}
return calculateDSTOffsetSimple(ms / msPerSecond, utcOffset);
}
