diff options
| author | Giuseppe D'Angelo <giuseppe.dangelo@kdab.com> | 2012-04-13 18:59:58 +0100 |
|---|---|---|
| committer | Qt by Nokia <qt-info@nokia.com> | 2012-04-14 15:49:16 +0200 |
| commit | c2293c897c9f2e35dffec777c19577c0f6052e81 (patch) | |
| tree | d64222df4200f01833bde36f41184f11ff19ce9f /src/corelib/tools | |
| parent | 5e24d22af075ce790b471fb9aca59a80037f34df (diff) | |
QHash: remove optimization for QHash<int, T>
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>
Diffstat (limited to 'src/corelib/tools')
| -rw-r--r-- | src/corelib/tools/qhash.h | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/src/corelib/tools/qhash.h b/src/corelib/tools/qhash.h index 1aa4fa7adc..e3188729c5 100644 --- a/src/corelib/tools/qhash.h +++ b/src/corelib/tools/qhash.h @@ -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 |