diff options
| -rw-r--r-- | src/corelib/time/qtimezoneprivate_win.cpp | 83 |
1 files changed, 56 insertions, 27 deletions
diff --git a/src/corelib/time/qtimezoneprivate_win.cpp b/src/corelib/time/qtimezoneprivate_win.cpp index 7ccad273ad..25a2ba5a39 100644 --- a/src/corelib/time/qtimezoneprivate_win.cpp +++ b/src/corelib/time/qtimezoneprivate_win.cpp @@ -321,6 +321,23 @@ qint64 calculateTransitionForYear(const SYSTEMTIME &rule, int year, int bias) return QTimeZonePrivate::invalidMSecs(); } +// True precisely if transition represents the start of the year. +bool isAtStartOfYear(const SYSTEMTIME &transition, int year) +{ + /* + Note that, here, wDay identifies an instance of a given day-of-week in the + month, with 5 meaning last. (December 31st is, incidentally, always the + fifth instance of its day of the week in its month. But we aren't testing + that - see below.) + + QDate represents Sunday by 7, SYSTEMTIME by 0; so compare day of the week + by taking difference mod 7. + */ + return transition.wMonth == 1 && transition.wDay == 1 + && (QDate(year, 1, 1).dayOfWeek() - transition.wDayOfWeek) % 7 == 0 + && transition.wHour == 0 && transition.wMinute == 0 && transition.wSecond == 0; +} + struct TransitionTimePair { // Transition times, in ms: @@ -342,16 +359,36 @@ struct TransitionTimePair year, or expresses a transition of each kind, even if standard time did change in a year with no DST. We've seen year-start fake-DST (whose offset matches prior standard offset, in which the previous - year ended); and conjecture that similar might be used at a year-end. - (This might be used for a southern-hemisphere zone, where the start of - the year usually is in DST, when applicable.) Note that, here, wDay - identifies an instance of a given day-of-week in the month, with 5 - meaning last. + year ended). + + It is possible there might also be year-end fake-DST but Bangladesh + toyed with DST from 2009-06-19 (a Friday) at 23:00 until, according to + the Olson database, 2009-12-32 24:00; however, MS represents that by + the last millisecond of the year, technically a millisecond early. (MS + falsely claims Bhutan did the same.) So we do not attempt to detect an + end-of-year fake transition; nor is there any reason to suppose MS + would need to do that, as anything it could implement thereby could + equally be implemented by a start-of-year fake. + + A fake transition at the start of the year tells us what the offset at + the start of the year is; if this doesn't match the offset in effect + at the end of the previous year, then it's a real transition. If it + does match, then we have a fake transition. (A fake transition of one + kind at the end of the year would be paired with a real transition, + allegedly of the other kind, part way through the year; that would be + a transition away from the offset that would nominally be restored by + the fake so, again, the year would have started with the post-fake + offset in effect.) Either the alleged standardTimeRule or the alleged daylightTimeRule may be faked; either way, the transition is actually a change to the current standard offset; but the unfaked half of the rule contains the - useful bias data, so we have to go along with its lies. + useful bias data, so we have to go along with its lies. Clients of + this class should still use DaylightTime and StandardTime as if the + fake were not a lie, selecting which side of the real transition to + use the data for, and ruleToData() will take care of extracting the + right offset based on that, while tagging the resulting Data as + standard time. Example: Russia/Moscow Format: -bias +( -stdBias, stdDate | -dstBias, dstDate ) notes @@ -361,25 +398,13 @@ struct TransitionTimePair Zone change in 2014: 180 +( 0, 0-10-5 2:0 | 60, 0-1-1 0:0 ) fake DST at year-start The last of these is missing on Win7 VMs (too old to know about it). */ - if (rule.daylightTimeRule.wMonth == 1 && rule.daylightTimeRule.wDay == 1) { - // Fake "DST transition" at start of year producing the same offset as - // previous year ended in. - if (rule.standardTimeBias + rule.daylightTimeBias == oldYearOffset) - dst = QTimeZonePrivate::invalidMSecs(); - } else if (rule.daylightTimeRule.wMonth == 12 && rule.daylightTimeRule.wDay > 3) { - // Similar, conjectured, for end of year, not changing offset. - if (rule.daylightTimeBias == 0) - dst = QTimeZonePrivate::invalidMSecs(); + if (rule.standardTimeBias + rule.daylightTimeBias == oldYearOffset + && isAtStartOfYear(rule.daylightTimeRule, year)) { + dst = QTimeZonePrivate::invalidMSecs(); } - if (rule.standardTimeRule.wMonth == 1 && rule.standardTimeRule.wDay == 1) { - // Fake "transition out of DST" at start of year producing the same - // offset as previous year ended in. - if (rule.standardTimeBias == oldYearOffset) - std = QTimeZonePrivate::invalidMSecs(); - } else if (rule.standardTimeRule.wMonth == 12 && rule.standardTimeRule.wDay > 3) { - // Similar, conjectured, for end of year, not changing offset. - if (rule.daylightTimeBias == 0) - std = QTimeZonePrivate::invalidMSecs(); + if (rule.standardTimeBias == oldYearOffset + && isAtStartOfYear(rule.standardTimeRule, year)) { + std = QTimeZonePrivate::invalidMSecs(); } } @@ -399,9 +424,13 @@ struct TransitionTimePair QTimeZonePrivate::Data ruleToData(const QWinTimeZonePrivate::QWinTransitionRule &rule, const QWinTimeZonePrivate *tzp, bool isDst) const { - if (isDst) - return tzp->ruleToData(rule, dst, QTimeZone::DaylightTime, fakesDst()); - return tzp->ruleToData(rule, std, QTimeZone::StandardTime, fakesDst()); + const auto type = isDst ? QTimeZone::DaylightTime : QTimeZone::StandardTime; + auto time = isDst ? dst : std; + // The isDst we're asked for may be set to the valid one of dst and + // std, when fake, but not always - so make sure: + if (time == QTimeZonePrivate::invalidMSecs()) + time = isDst ? std : dst; + return tzp->ruleToData(rule, time, type, fakesDst()); } }; |