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Simplify one of the gap cases in QTimeZonePrivate::dataForLocalTime()

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The code computed the transition gap and subtracted it from one side's
proposed UTC time, or added it to the other's; the effect was the same
as swapping these two values. Doing that overtly as a swap simplifies
the remainder of the code. Clarified the accompanying comment in the
process.

Change-Id: I00b8d2bb98ea08b6edd11e01d05a091cb39f3511
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Edward Welbourne 2022-08-25 14:07:25 +02:00
parent a6d6d919fa
commit 981b3336f6
1 changed files with 5 additions and 11 deletions
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16
src/corelib/time/qtimezoneprivate.cpp
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@ -340,18 +340,12 @@ QTimeZonePrivate::Data QTimeZonePrivate::dataForLocalTime(qint64 forLocalMSecs,
/*
Neither is valid (e.g. in a spring-forward's gap) and
nextTran.atMSecsSinceEpoch < nextStart <= tran.atMSecsSinceEpoch, so
0 < tran.atMSecsSinceEpoch - nextTran.atMSecsSinceEpoch
= (nextTran.offsetFromUtc - tran.offsetFromUtc) * 1000
nextTran.atMSecsSinceEpoch < nextStart <= tran.atMSecsSinceEpoch;
swap their atMSecsSinceEpoch to give each a moment on its side of
the transition; and pick the reverse of what hint asked for:
*/
int dstStep = (nextTran.offsetFromUtc - tran.offsetFromUtc) * 1000;
Q_ASSERT(dstStep > 0); // How else could we get here ?
if (nextFirst) { // hint thought we needed nextTran, so use tran
tran.atMSecsSinceEpoch -= dstStep;
return tran;
}
nextTran.atMSecsSinceEpoch += dstStep;
return nextTran;
std::swap(tran.atMSecsSinceEpoch, nextTran.atMSecsSinceEpoch);
return nextFirst ? tran : nextTran;
}
// Before first transition, or system has transitions but not for this zone.
// Try falling back to offsetFromUtc (works for before first transition, at least).