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| author | PeterN <peter@fuzzle.org> | 2018-05-19 22:04:25 +0100 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2018-05-19 22:04:25 +0100 |
| commit | 8a7de364639c23d6a08ee07698f7a04b499ccdc5 (patch) | |
| tree | 796e177d9fbe837e0d2e5feca3e3f255d8b6192e /src/misc | |
| parent | 7bd2fa351653b0140c82fcad96a0f3b16758a0b0 (diff) | |
| download | openttd-8a7de364639c23d6a08ee07698f7a04b499ccdc5.tar.xz | |
Change [#6689]: Tweak HashTable hash calculation to reduce collisions. (kernigh2) (#6786)
Diffstat (limited to 'src/misc')
| -rw-r--r-- | src/misc/hashtable.hpp | 10 |
1 files changed, 4 insertions, 6 deletions
diff --git a/src/misc/hashtable.hpp b/src/misc/hashtable.hpp index 1afe58cac..1078f1861 100644 --- a/src/misc/hashtable.hpp +++ b/src/misc/hashtable.hpp @@ -161,12 +161,10 @@ protected: /** static helper - return hash for the given key modulo number of slots */ inline static int CalcHash(const Tkey &key) { - int32 hash = key.CalcHash(); - if ((8 * Thash_bits) < 32) hash ^= hash >> (min(8 * Thash_bits, 31)); - if ((4 * Thash_bits) < 32) hash ^= hash >> (min(4 * Thash_bits, 31)); - if ((2 * Thash_bits) < 32) hash ^= hash >> (min(2 * Thash_bits, 31)); - if ((1 * Thash_bits) < 32) hash ^= hash >> (min(1 * Thash_bits, 31)); - hash &= (1 << Thash_bits) - 1; + uint32 hash = key.CalcHash(); + hash -= (hash >> 17); // hash * 131071 / 131072 + hash -= (hash >> 5); // * 31 / 32 + hash &= (1 << Thash_bits) - 1; // modulo slots return hash; } |