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Bug 834988 - Invert the meaning of LocalUTCDifferenceSeconds and rename it to UTCToLocalStandardOffsetSeconds. This gives it the same sign/semantics (if different units) as the -8 in UTC-8, and it makes it consistent with ES5's LocalTZA concept. Also add an interface comment with two examples of its behavior. r=dmandelin

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--HG--
extra : rebase_source : 3e56a9fcc590c6b42c2782bd30431db8f3464825
This commit is contained in:
Jeff Walden 2013-01-25 15:46:10 -08:00
parent 022804a80d
commit 7f65bf94ef
1 changed files with 30 additions and 19 deletions
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49
js/src/vm/DateTime.cpp
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@ -38,8 +38,22 @@ ComputeUTCTime(time_t t, struct tm *ptm)
#endif
}
/*
* Compute the offset in seconds from the current UTC time to the current local
* standard time (i.e. not including any offset due to DST).
*
* Examples:
*
* Suppose we are in California, USA on January 1, 2013 at 04:00 PST (UTC-8, no
* DST in effect), corresponding to 12:00 UTC. This function would then return
* -8 * SecondsPerHour, or -28800.
*
* Or suppose we are in Berlin, Germany on July 1, 2013 at 17:00 CEST (UTC+2,
* DST in effect), corresponding to 15:00 UTC. This function would then return
* +1 * SecondsPerHour, or +3600.
*/
static int32_t
LocalUTCDifferenceSeconds()
UTCToLocalStandardOffsetSeconds()
{
using js::SecondsPerDay;
using js::SecondsPerHour;
@ -96,24 +110,24 @@ LocalUTCDifferenceSeconds()
int utc_secs = utc.tm_hour * SecondsPerHour + utc.tm_min * SecondsPerMinute;
int local_secs = local.tm_hour * SecondsPerHour + local.tm_min * SecondsPerMinute;
// Callers expect the negative difference of the offset from local time
// and UTC.
// Same-day? Just subtract the seconds counts.
if (utc.tm_mday == local.tm_mday)
return utc_secs - local_secs;
return local_secs - utc_secs;
// Local date comes after UTC (offset in the positive range).
// If we have more UTC seconds, move local seconds into the UTC seconds'
// frame of reference and then subtract.
if (utc_secs > local_secs)
return utc_secs - (SecondsPerDay + local_secs);
return (SecondsPerDay + local_secs) - utc_secs;
// Local date comes before UTC (offset in the negative range).
return (utc_secs + SecondsPerDay) - local_secs;
// Otherwise we have more local seconds, so move the UTC seconds into the
// local seconds' frame of reference and then subtract.
return local_secs - (utc_secs + SecondsPerDay);
}
void
js::DateTimeInfo::updateTimeZoneAdjustment()
{
double newTZA = -(LocalUTCDifferenceSeconds() * msPerSecond);
double newTZA = UTCToLocalStandardOffsetSeconds() * msPerSecond;
if (newTZA == localTZA_)
return;
@ -153,11 +167,9 @@ js::DateTimeInfo::computeDSTOffsetMilliseconds(int64_t localTimeSeconds)
MOZ_ASSERT(localTimeSeconds <= MaxUnixTimeT);
#if defined(XP_WIN)
/* Windows does not follow POSIX. Updates to the
* TZ environment variable are not reflected
* immediately on that platform as they are
* on UNIX systems without this call.
*/
// Windows does not follow POSIX. Updates to the TZ environment variable
// are not reflected immediately on that platform as they are on UNIX
// systems without this call.
_tzset();
#endif
@ -165,11 +177,10 @@ js::DateTimeInfo::computeDSTOffsetMilliseconds(int64_t localTimeSeconds)
if (!ComputeLocalTime(static_cast<time_t>(localTimeSeconds), &tm))
return 0;
int32_t base = LocalUTCDifferenceSeconds();
int32_t utcToLocalOffsetSeconds = UTCToLocalStandardOffsetSeconds();
int32_t dayoff = int32_t((localTimeSeconds - base) % (SecondsPerHour * 24));
int32_t tmoff = tm.tm_sec + (tm.tm_min * SecondsPerMinute) +
(tm.tm_hour * SecondsPerHour);
int32_t dayoff = int32_t((localTimeSeconds + utcToLocalOffsetSeconds) % SecondsPerDay);
int32_t tmoff = tm.tm_sec + (tm.tm_min * SecondsPerMinute) + (tm.tm_hour * SecondsPerHour);
int32_t diff = tmoff - dayoff;