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Improve qHash(QFont)

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When the families member was added to QFontDef, it was included
in op== and qHash(), however the seed was passed to two qHash()
calls for subobjects. With xor used as the combiner, it could
happen that the seed was xored out (e.g. on empty strings),
leaving a slight opening for prediciable hash values.

Fix by using QtPrivate::QHashCombine, which handles the seed in
such a way as to avoid the issue.

Change-Id: I8a3e4c2f368306446554249763695158df5ac634
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
This commit is contained in:
Marc Mutz 2019-05-27 16:12:17 +02:00
parent fbb2ed1505
commit 5ef6e1fa54
1 changed files with 14 additions and 13 deletions
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27
src/gui/text/qfont_p.h
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@ -138,19 +138,20 @@ struct QFontDef
inline uint qHash(const QFontDef &fd, uint seed = 0) noexcept
{
return qHash(qRound64(fd.pixelSize*10000)) // use only 4 fractional digits
^ qHash(fd.weight)
^ qHash(fd.style)
^ qHash(fd.stretch)
^ qHash(fd.styleHint)
^ qHash(fd.styleStrategy)
^ qHash(fd.ignorePitch)
^ qHash(fd.fixedPitch)
^ qHash(fd.family, seed)
^ qHash(fd.families, seed)
^ qHash(fd.styleName)
^ qHash(fd.hintingPreference)
;
QtPrivate::QHashCombine hash;
seed = hash(seed, qRound64(fd.pixelSize*10000)); // use only 4 fractional digits
seed = hash(seed, fd.weight);
seed = hash(seed, fd.style);
seed = hash(seed, fd.stretch);
seed = hash(seed, fd.styleHint);
seed = hash(seed, fd.styleStrategy);
seed = hash(seed, fd.ignorePitch);
seed = hash(seed, fd.fixedPitch);
seed = hash(seed, fd.family);
seed = hash(seed, fd.families);
seed = hash(seed, fd.styleName);
seed = hash(seed, fd.hintingPreference);
return seed;
}
class QFontEngineData