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Break out overflow-calculations into semantically-named inlines

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Adding days to seconds or millis, or seconds to millis, involves
scaling one and adding the other, so has to check for overflow. The
std::integral_constant boilerplate and the complications of calling
mul_overflow() and add_overflow() rather hid what was going on, so
package them in inlines so that their calls are more intelligible.

Change-Id: I1e90de8fcb81eb84920868c7e4bd217ee353fc54
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
This commit is contained in:
Edward Welbourne 2022-08-08 18:27:01 +02:00
parent acb2faf1fe
commit b9baa42b62
2 changed files with 35 additions and 22 deletions
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20
src/corelib/time/qdatetime.cpp
View File

@ -2451,6 +2451,14 @@ static QTime msecsToTime(qint64 msecs)
return QTime::fromMSecsSinceStartOfDay(QRoundingDown::qMod(msecs, MSECS_PER_DAY));
}
// True if combining days with millis overflows; otherwise, stores result in *sumMillis
// The inputs should not have opposite signs.
static inline bool daysAndMillisOverflow(qint64 days, qint64 millisInDay, qint64 *sumMillis)
{
return mul_overflow(days, std::integral_constant<qint64, MSECS_PER_DAY>(), sumMillis)
|| add_overflow(*sumMillis, millisInDay, sumMillis);
}
// Converts a date/time value into msecs
static qint64 timeToMSecs(QDate date, QTime time)
{
@ -2460,8 +2468,7 @@ static qint64 timeToMSecs(QDate date, QTime time)
++days;
dayms -= MSECS_PER_DAY;
}
if (mul_overflow(days, std::integral_constant<qint64, MSECS_PER_DAY>(), &msecs)
|| add_overflow(msecs, dayms, &msecs)) {
if (daysAndMillisOverflow(days, dayms, &msecs)) {
using Bound = std::numeric_limits<qint64>;
return days < 0 ? Bound::min() : Bound::max();
}
@ -2584,13 +2591,11 @@ static auto millisToWithinRange(qint64 millis)
qint64 shifted = 0;
bool good = false;
} result;
qint64 jd = msecsToJulianDay(millis), fakeJd, diffMillis;
qint64 jd = msecsToJulianDay(millis), fakeJd;
auto ymd = QGregorianCalendar::partsFromJulian(jd);
result.good = QGregorianCalendar::julianFromParts(systemTimeYearMatching(ymd.year),
ymd.month, ymd.day, &fakeJd)
&& !mul_overflow(fakeJd - jd, std::integral_constant<qint64, MSECS_PER_DAY>(),
&diffMillis)
&& !add_overflow(diffMillis, millis, &result.shifted);
&& !daysAndMillisOverflow(fakeJd - jd, millis, &result.shifted);
return result;
}
@ -2951,8 +2956,7 @@ static void setDateTime(QDateTimeData &d, QDate date, QTime time)
// Check in representable range:
qint64 msecs = 0;
if (mul_overflow(days, std::integral_constant<qint64, MSECS_PER_DAY>(), &msecs)
|| add_overflow(msecs, qint64(ds), &msecs)) {
if (daysAndMillisOverflow(days, qint64(ds), &msecs)) {
newStatus = QDateTimePrivate::StatusFlags{};
msecs = 0;
}

37
src/corelib/time/qlocaltime.cpp
View File

@ -283,6 +283,24 @@ int getUtcOffset(qint64 atMSecsSinceEpoch)
}
#endif // QT_BOOTSTRAPPED
#define IC(N) std::integral_constant<qint64, N>()
// True if combining day and seconds overflows qint64; otherwise, sets *epochSeconds
inline bool daysAndSecondsOverflow(qint64 julianDay, qint64 daySeconds, qint64 *epochSeconds)
{
return mul_overflow(julianDay - JULIAN_DAY_FOR_EPOCH, IC(SECS_PER_DAY), epochSeconds)
|| add_overflow(*epochSeconds, daySeconds, epochSeconds);
}
// True if combining seconds and millis overflows; otherwise sets *epochMillis
inline bool secondsAndMillisOverflow(qint64 epochSeconds, qint64 millis, qint64 *epochMillis)
{
return mul_overflow(epochSeconds, IC(MSECS_PER_SEC), epochMillis)
|| add_overflow(*epochMillis, millis, epochMillis);
}
#undef IC
// Calls the platform variant of localtime() for the given utcMillis, and
// returns the local milliseconds, offset from UTC and DST status.
QDateTimePrivate::ZoneState utcToLocal(qint64 utcMillis)
@ -306,13 +324,8 @@ QDateTimePrivate::ZoneState utcToLocal(qint64 utcMillis)
const qint64 daySeconds = tmSecsWithinDay(local);
Q_ASSERT(0 <= daySeconds && daySeconds < SECS_PER_DAY);
qint64 localSeconds, localMillis;
if (Q_UNLIKELY(
mul_overflow(jd - JULIAN_DAY_FOR_EPOCH, std::integral_constant<qint64, SECS_PER_DAY>(),
&localSeconds)
|| add_overflow(localSeconds, daySeconds, &localSeconds)
|| mul_overflow(localSeconds, std::integral_constant<qint64, MSECS_PER_SEC>(),
&localMillis)
|| add_overflow(localMillis, qint64(msec), &localMillis))) {
if (Q_UNLIKELY(daysAndSecondsOverflow(jd, daySeconds, &localSeconds)
|| secondsAndMillisOverflow(localSeconds, qint64(msec), &localMillis))) {
return {utcMillis};
}
const auto dst
@ -362,11 +375,9 @@ QDateTimePrivate::ZoneState mapLocalTime(qint64 local, QDateTimePrivate::Dayligh
daySecs -= SECS_PER_DAY;
}
qint64 localSecs;
if (Q_UNLIKELY(mul_overflow(jd - JULIAN_DAY_FOR_EPOCH,
std::integral_constant<qint64, SECS_PER_DAY>(), &localSecs)
|| add_overflow(localSecs, daySecs, &localSecs))) {
if (Q_UNLIKELY(daysAndSecondsOverflow(jd, daySecs, &localSecs)))
return {local, offset, dst, false};
}
offset = localSecs - utcSecs;
if (localSecs < 0 && millis > 0) {
@ -374,9 +385,7 @@ QDateTimePrivate::ZoneState mapLocalTime(qint64 local, QDateTimePrivate::Dayligh
millis -= MSECS_PER_SEC;
}
qint64 revised;
const bool overflow =
mul_overflow(localSecs, std::integral_constant<qint64, MSECS_PER_SEC>(), &revised)
|| add_overflow(revised, millis, &revised);
const bool overflow = secondsAndMillisOverflow(localSecs, millis, &revised);
return {overflow ? local : revised, offset, dst, !overflow};
}