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QHash: remove optimization for QHash<int, T>

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QHash employs an optimization for int/uints, squashing the hash
value and the key value inside an union. This obviously works
iff qHash(int k) = k. If the hash value gets salted, the hash
table is corrupted.

This patch removes that optimization by means of a #if 0,
so if further research finds out that we want those 4 bytes back
it's pretty simple to revert.

Change-Id: If273f0bf2ff007f4f2f7c46d2aab364a3b455cf1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Giuseppe D'Angelo 2012-04-13 18:59:58 +01:00 committed by Qt by Nokia
parent 5e24d22af0
commit c2293c897c
1 changed files with 14 additions and 1 deletions
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15
src/corelib/tools/qhash.h
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@ -218,7 +218,19 @@ struct QHashNode
inline bool same_key(uint h0, const Key &key0) { return h0 == h && key0 == key; }
};
#if 0
// ###
// The introduction of the QHash random seed breaks this optimization, as it
// relies on qHash(int i) = i. If the hash value is salted, then the hash
// table becomes corrupted.
//
// A bit more research about whether it makes sense or not to salt integer
// keys (and in general keys whose hash value is easy to invert)
// is needed, or about how keep this optimization and the seed (f.i. by
// specializing QHash for integer values, and re-apply the seed during lookup).
//
// Be aware that such changes can easily be binary incompatible, and therefore
// cannot be made during the Qt 5 lifetime.
#define Q_HASH_DECLARE_INT_NODES(key_type) \
template <class T> \
struct QHashDummyNode<key_type, T> { \
@ -246,6 +258,7 @@ Q_HASH_DECLARE_INT_NODES(ushort);
Q_HASH_DECLARE_INT_NODES(int);
Q_HASH_DECLARE_INT_NODES(uint);
#undef Q_HASH_DECLARE_INT_NODES
#endif // #if 0
template <class Key, class T>
class QHash