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Rework setMSecsSinceEpoch() to avoid local->UTC conversions

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The function takes a UTC time, which it converts to local time when
needed, but its (two) calls to refresh a local time instance were
doing the (more expensive) reverse conversion, which we don't need
(because we knew UTC to start with) and, in this case, it can't land
on an invalid time, so we don't need to cope with that.

Change-Id: I49b42bfa9f6a5fde12810f5a0da9ff4466ca86a4
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
This commit is contained in:
Edward Welbourne 2021-03-01 12:08:17 +01:00
parent fd5b92c2ba
commit 74eddd5bf0
1 changed files with 42 additions and 45 deletions
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87
src/corelib/time/qdatetime.cpp
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@ -4005,63 +4005,60 @@ void QDateTime::setMSecsSinceEpoch(qint64 msecs)
{
auto status = getStatus(d);
const auto spec = extractSpec(status);
Q_ASSERT(spec == Qt::UTC || spec == Qt::LocalTime || !d.isShort());
qint64 local = msecs;
int offsetFromUtc = 0;
status &= ~QDateTimePrivate::ValidityMask;
switch (spec) {
case Qt::UTC:
status |= QDateTimePrivate::ValidWhenMask;
break;
case Qt::OffsetFromUTC:
if (!add_overflow(msecs, d->m_offsetFromUtc * MSECS_PER_SEC, &msecs))
if (spec == Qt::UTC || spec == Qt::OffsetFromUTC) {
if (spec == Qt::OffsetFromUTC)
offsetFromUtc = d->m_offsetFromUtc;
if (!offsetFromUtc || !add_overflow(msecs, offsetFromUtc * MSECS_PER_SEC, &local))
status |= QDateTimePrivate::ValidWhenMask;
break;
case Qt::TimeZone:
Q_ASSERT(!d.isShort());
#if QT_CONFIG(timezone)
d.detach();
if (!d->m_timeZone.isValid())
break;
status = mergeDaylightStatus(status,
d->m_timeZone.d->isDaylightTime(msecs)
? QDateTimePrivate::DaylightTime
: QDateTimePrivate::StandardTime);
d->m_offsetFromUtc = d->m_timeZone.d->offsetFromUtc(msecs);
// NB: cast to qint64 here is important to make sure a matching
// add_overflow is found, GCC 7.5.0 fails without this cast
if (!add_overflow(msecs, qint64(d->m_offsetFromUtc * MSECS_PER_SEC), &msecs))
status |= QDateTimePrivate::ValidWhenMask;
#endif // timezone
break;
case Qt::LocalTime: {
QDate dt;
QTime tm;
QDateTimePrivate::DaylightStatus dstStatus;
if (QDateTimePrivate::epochMSecsToLocalTime(msecs, &dt, &tm, &dstStatus)) {
setDateTime(d, dt, tm);
} else {
auto dst = extractDaylightStatus(status);
if (spec == Qt::LocalTime) {
QDate dt;
QTime tm;
if (QDateTimePrivate::epochMSecsToLocalTime(msecs, &dt, &tm, &dst))
setDateTime(d, dt, tm);
status = getStatus(d);
if ((status & QDateTimePrivate::ValidDate) && (status & QDateTimePrivate::ValidTime)) {
local = getMSecs(d);
offsetFromUtc = (local - msecs) / MSECS_PER_SEC;
status |= QDateTimePrivate::ValidWhenMask;
}
#if QT_CONFIG(timezone)
} else if (spec == Qt::TimeZone && (d.detach(), d->m_timeZone.isValid())) {
const auto data = d->m_timeZone.d->data(msecs);
if (data.offsetFromUtc != QTimeZonePrivate::invalidSeconds()) {
dst = data.daylightTimeOffset
? QDateTimePrivate::DaylightTime
: QDateTimePrivate::StandardTime;
offsetFromUtc = data.offsetFromUtc;
if (!offsetFromUtc
// NB: cast to qint64 here is important to make sure a matching
// add_overflow is found, GCC 7.5.0 fails without this cast
|| !add_overflow(msecs, qint64(offsetFromUtc * MSECS_PER_SEC), &local)) {
status |= QDateTimePrivate::ValidWhenMask;
}
}
#endif // timezone
}
if ((status & QDateTimePrivate::ValidDate) && (status & QDateTimePrivate::ValidTime)) {
refreshZonedDateTime(d, spec); // FIXME: we do this again, below
msecs = getMSecs(d);
status = mergeDaylightStatus(getStatus(d), dstStatus);
}
break;
}
status = mergeDaylightStatus(status, dst);
}
Q_ASSERT(!(status & QDateTimePrivate::ValidDateTime)
|| (offsetFromUtc >= -SECS_PER_DAY && offsetFromUtc <= SECS_PER_DAY));
if (msecsCanBeSmall(msecs) && d.isShort()) {
if (msecsCanBeSmall(local) && d.isShort()) {
// we can keep short
d.data.msecs = qintptr(msecs);
d.data.msecs = qintptr(local);
d.data.status = status.toInt();
} else {
d.detach();
d->m_status = status & ~QDateTimePrivate::ShortData;
d->m_msecs = msecs;
}
if (spec == Qt::LocalTime || spec == Qt::TimeZone) {
refreshZonedDateTime(d, spec);
Q_ASSERT((d.isShort() ? d.data.msecs : d->m_msecs) == msecs);
d->m_msecs = local;
d->m_offsetFromUtc = offsetFromUtc;
}
}