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QTimeZonePrivate::dataForLocalTime(): cope with negative DST offsets

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The tz database's latest update now records the cases where summer
time is deemed standard and winter-time is deemed DST.  (This doesn't
change what the offsets are, just how they're described.)  The
resulting negative DST offsets mess up the algorithm for converting
local time to UTC, causing tst_QTimeZone::transitionEachZone() to fail
for Europe/Dublin in the hour before its transition; so refine the
algorithm to cope with the new case.

Task-number: QTBUG-69980
Change-Id: I24003872fffb03b2903161859158d0ce998b3073
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Edward Welbourne 2018-08-17 11:19:32 +02:00 committed by Tony Sarajärvi
parent 346c15102b
commit fe9a37ac48
1 changed files with 7 additions and 5 deletions
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12
src/corelib/tools/qtimezoneprivate.cpp
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@ -357,10 +357,10 @@ QTimeZonePrivate::Data QTimeZonePrivate::dataForLocalTime(qint64 forLocalMSecs,
/*
So now tran is definitely before and nextTran is either after or only
slightly before. The one with the larger offset is in DST; the other in
standard time. Our hint tells us which of those to use (defaulting to
standard if no hint): try it first; if that fails, try the other; if both
fail life's tricky.
slightly before. One is standard time; we interpret the other as DST
(although the transition might in fact by a change in standard offset). Our
hint tells us which of those to use (defaulting to standard if no hint): try
it first; if that fails, try the other; if both fail, life's tricky.
*/
Q_ASSERT(forLocalMSecs < 0
|| forLocalMSecs - tran.offsetFromUtc * 1000 > tran.atMSecsSinceEpoch);
@ -369,7 +369,9 @@ QTimeZonePrivate::Data QTimeZonePrivate::dataForLocalTime(qint64 forLocalMSecs,
nextTran.atMSecsSinceEpoch = forLocalMSecs - nextTran.offsetFromUtc * 1000;
tran.atMSecsSinceEpoch = forLocalMSecs - tran.offsetFromUtc * 1000;
const bool nextIsDst = tran.offsetFromUtc < nextTran.offsetFromUtc;
// If both or neither have zero DST, treat the one with lower offset as standard:
const bool nextIsDst = !nextTran.daylightTimeOffset == !tran.daylightTimeOffset
? tran.offsetFromUtc < nextTran.offsetFromUtc : nextTran.daylightTimeOffset;
// If that agrees with hint > 0, our first guess is to use nextTran; else tran.
const bool nextFirst = nextIsDst == (hint > 0) && nextStart != invalidMSecs();
for (int i = 0; i < 2; i++) {