Improve qHash(QFont)

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>
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

1 files changed, 14 insertions, 13 deletions

diff --git a/src/gui/text/qfont_p.h b/src/gui/text/qfont_p.h
index db74ab0b65..466e19e9cc 100644
--- a/src/gui/text/qfont_p.h
+++ b/src/gui/text/qfont_p.h
@@ -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