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Rearrange mapLocalTime() so its millis always have the right sign

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Doing a simple division to get seconds, before using rounding-down
division to get days and positive seconds, saves the need to check for
seconds and millis in opposite directions that might cause a needless
overflow when computing the final result.

Change-Id: Ia4f95bb0510eb4f2c1f9131a34d317bd41bbed2a
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
This commit is contained in:
Edward Welbourne 2022-08-10 16:29:39 +02:00
parent 854cb55987
commit 0acb56518d
1 changed files with 12 additions and 11 deletions
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23
src/corelib/time/qlocaltime.cpp
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@ -348,11 +348,13 @@ QString localTimeAbbbreviationAt(qint64 local, QDateTimePrivate::DaylightStatus
QDateTimePrivate::ZoneState mapLocalTime(qint64 local, QDateTimePrivate::DaylightStatus dst)
{
const qint64 localDays = QRoundingDown::qDiv(local, MSECS_PER_DAY);
qint64 millis = local - localDays * MSECS_PER_DAY;
Q_ASSERT(0 <= millis && millis < MSECS_PER_DAY); // Definition of QRD::qDiv.
struct tm tmLocal = timeToTm(localDays, int(millis / MSECS_PER_SEC), dst);
millis %= MSECS_PER_SEC;
qint64 localSecs = local / MSECS_PER_SEC;
qint64 millis = local - localSecs * MSECS_PER_SEC; // 0 or with same sign as local
const qint64 localDays = QRoundingDown::qDiv(localSecs, SECS_PER_DAY);
qint64 daySecs = localSecs - localDays * SECS_PER_DAY;
Q_ASSERT(0 <= daySecs && daySecs < SECS_PER_DAY); // Definition of QRD::qDiv.
struct tm tmLocal = timeToTm(localDays, daySecs, dst);
time_t utcSecs;
if (!callMkTime(&tmLocal, &utcSecs))
return {local};
@ -368,22 +370,21 @@ QDateTimePrivate::ZoneState mapLocalTime(qint64 local, QDateTimePrivate::Dayligh
&jd))) {
return {local, offset, dst, false};
}
qint64 daySecs = tmSecsWithinDay(tmLocal);
daySecs = tmSecsWithinDay(tmLocal);
Q_ASSERT(0 <= daySecs && daySecs < SECS_PER_DAY);
if (daySecs > 0 && jd < JULIAN_DAY_FOR_EPOCH) {
++jd;
daySecs -= SECS_PER_DAY;
}
qint64 localSecs;
if (Q_UNLIKELY(daysAndSecondsOverflow(jd, daySecs, &localSecs)))
return {local, offset, dst, false};
offset = localSecs - utcSecs;
if (localSecs < 0 && millis > 0) {
++localSecs;
millis -= MSECS_PER_SEC;
}
// The only way localSecs and millis can now have opposite sign is for
// resolution of the local time to have kicked us across the epoch, in which
// case there's no danger of overflow. So if overflow is in danger of
// happening, we're already doing the best we can to avoid it.
qint64 revised;
const bool overflow = secondsAndMillisOverflow(localSecs, millis, &revised);
return {overflow ? local : revised, offset, dst, !overflow};