cpp/openttd-patchpack/source Changeset - r22864:621b56e45870

Changeset - r22864:621b56e45870

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PeterN - 6 years ago 2018-05-19 21:04:25
peter@fuzzle.org

Change [#6689]: Tweak HashTable hash calculation to reduce collisions. (kernigh2) (#6786)

1 file changed with 4 insertions and 6 deletions:

src/misc/hashtable.hpp

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src/misc/hashtable.hpp

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@@ @@ -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;
+	}

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