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Add some local const variables to save some repeated computation

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QTimeZonePrivate::dataForLocalTime() makes repeated use of the times
sixteen hours before and after the target local time, so compute those
up front once instead of each time they're needed, giving them
expressive names and making code terser.

Change-Id: I4b682cc6de2adb98c3ee5489eec4b63ac1090961
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Edward Welbourne 2018-08-17 13:07:14 +02:00
parent 67984b265a
commit e4cee4bd57
1 changed files with 7 additions and 8 deletions
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15
src/corelib/tools/qtimezoneprivate.cpp
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@ -260,6 +260,8 @@ QTimeZonePrivate::Data QTimeZonePrivate::dataForLocalTime(qint64 forLocalMSecs,
const qint64 sixteenHoursInMSecs(16 * 3600 * 1000);
Q_STATIC_ASSERT(-sixteenHoursInMSecs / 1000 < QTimeZone::MinUtcOffsetSecs
&& sixteenHoursInMSecs / 1000 > QTimeZone::MaxUtcOffsetSecs);
const qint64 recent = forLocalMSecs - sixteenHoursInMSecs;
const qint64 imminent = forLocalMSecs + sixteenHoursInMSecs;
/*
Offsets are Local - UTC, positive to the east of Greenwich, negative to
the west; DST offset always exceeds standard offset, when DST applies.
@ -327,7 +329,7 @@ QTimeZonePrivate::Data QTimeZonePrivate::dataForLocalTime(qint64 forLocalMSecs,
// Get a transition definitely before the local MSecs; usually all we need.
// Only around the transition times might we need another.
Data tran = previousTransition(forLocalMSecs - sixteenHoursInMSecs);
Data tran = previousTransition(recent);
Q_ASSERT(forLocalMSecs < 0 || // Pre-epoch TZ info may be unavailable
forLocalMSecs - tran.offsetFromUtc * 1000 >= tran.atMSecsSinceEpoch);
Data nextTran = nextTransition(tran.atMSecsSinceEpoch);
@ -343,8 +345,7 @@ QTimeZonePrivate::Data QTimeZonePrivate::dataForLocalTime(qint64 forLocalMSecs,
&& forLocalMSecs > nextTran.atMSecsSinceEpoch + nextTran.offsetFromUtc * 1000) {
Data newTran = nextTransition(nextTran.atMSecsSinceEpoch);
if (newTran.atMSecsSinceEpoch == invalidMSecs()
|| newTran.atMSecsSinceEpoch + newTran.offsetFromUtc * 1000
> forLocalMSecs + sixteenHoursInMSecs) {
|| newTran.atMSecsSinceEpoch + newTran.offsetFromUtc * 1000 > imminent) {
// Definitely not a relevant tansition: too far in the future.
break;
}
@ -417,8 +418,8 @@ QTimeZonePrivate::Data QTimeZonePrivate::dataForLocalTime(qint64 forLocalMSecs,
/* Bracket and refine to discover offset. */
qint64 utcEpochMSecs;
int early = offsetFromUtc(forLocalMSecs - sixteenHoursInMSecs);
int late = offsetFromUtc(forLocalMSecs + sixteenHoursInMSecs);
int early = offsetFromUtc(recent);
int late = offsetFromUtc(imminent);
if (Q_LIKELY(early == late)) { // > 99% of the time
utcEpochMSecs = forLocalMSecs - early * 1000;
} else {
@ -439,9 +440,7 @@ QTimeZonePrivate::Data QTimeZonePrivate::dataForLocalTime(qint64 forLocalMSecs,
utcEpochMSecs = forStd;
} else {
// Invalid forLocalMSecs: in spring-forward gap.
const int dstStep = daylightTimeOffset(early < late ?
forLocalMSecs + sixteenHoursInMSecs :
forLocalMSecs - sixteenHoursInMSecs);
const int dstStep = daylightTimeOffset(early < late ? imminent : recent);
Q_ASSERT(dstStep); // There can't be a transition without it !
utcEpochMSecs = (hint > 0) ? forStd - dstStep : forDst + dstStep;
}