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Add hash_combine64.
Extracted from a larger patch by Amul Sul, with some comment additions by me. Discussion: http://postgr.es/m/20171024113004.hn5qajypin4dy5sw@alap3.anarazel.de
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@ -8,8 +8,8 @@
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#define HASHUTILS_H
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/*
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* Combine two hash values, resulting in another hash value, with decent bit
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* mixing.
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* Combine two 32-bit hash values, resulting in another hash value, with
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* decent bit mixing.
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*
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* Similar to boost's hash_combine().
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*/
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@ -20,6 +20,18 @@ hash_combine(uint32 a, uint32 b)
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return a;
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}
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/*
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* Combine two 64-bit hash values, resulting in another hash value, using the
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* same kind of technique as hash_combine(). Testing shows that this also
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* produces good bit mixing.
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*/
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static inline uint64
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hash_combine64(uint64 a, uint64 b)
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{
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/* 0x49a0f4dd15e5a8e3 is 64bit random data */
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a ^= b + 0x49a0f4dd15e5a8e3 + (a << 54) + (a >> 7);
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return a;
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}
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/*
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* Simple inline murmur hash implementation hashing a 32 bit integer, for
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