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Clip dataForLocalTime()'s bracketing window's start to minMSecs() + 1 

The minMSecs() itself is one more than the type's min(), which is used
as invalidMSecs(). As (at least) the Windows back-end uses minMSecs()
as the time of a start-of-time transition (that we'd like to find as
our current transition), use one more than it as lower-bound for where
to search from for a previous transition, so that we do find that
first ever transition.

Pick-to: 6.3
Change-Id: Iae861e740e02bd38ffb2af77aff625d3b48182d2
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
bb10
Edward Welbourne 2022-02-23 12:22:44 +01:00
parent 8024498a36
commit 4959f8a34b
1 changed files with 9 additions and 5 deletions
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14
src/corelib/time/qtimezoneprivate.cpp
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@ -225,14 +225,18 @@ QTimeZonePrivate::Data QTimeZonePrivate::dataForLocalTime(qint64 forLocalMSecs,
static_assert(-sixteenHoursInMSecs / 1000 < QTimeZone::MinUtcOffsetSecs
&& sixteenHoursInMSecs / 1000 > QTimeZone::MaxUtcOffsetSecs);
qint64 millis;
// Clip the bracketing times to the bounds of the supported range. Exclude
// minMSecs(), because at least one backend (Windows) uses it for a
// start-of-time fake transition, that we want previousTransition() to find.
const qint64 recent =
sub_overflow(forLocalMSecs, sixteenHoursInMSecs, &millis)
? minMSecs() : millis;
sub_overflow(forLocalMSecs, sixteenHoursInMSecs, &millis) || millis <= minMSecs()
? minMSecs() + 1 : millis; // Necessarily <= forLocalMSecs + 2.
// (Given that minMSecs() is std::numeric_limits<qint64>::min() + 1.)
const qint64 imminent =
add_overflow(forLocalMSecs, sixteenHoursInMSecs, &millis)
? maxMSecs() : millis;
// At most one of those took the boundary value:
Q_ASSERT(recent < imminent && sixteenHoursInMSecs < imminent - recent + 1);
? maxMSecs() : millis; // Necessarily >= forLocalMSecs
// At most one of those was clipped to its boundary value:
Q_ASSERT(recent < imminent && sixteenHoursInMSecs < imminent - recent + 2);
/*
Offsets are Local - UTC, positive to the east of Greenwich, negative to
the west; DST offset always exceeds standard offset, when DST applies.