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54 lines
1.1 KiB
C
54 lines
1.1 KiB
C
/*
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* Utilities for working with hash values.
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*
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* Portions Copyright (c) 2017-2019, PostgreSQL Global Development Group
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*/
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#ifndef HASHUTILS_H
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#define HASHUTILS_H
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/*
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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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static inline uint32
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hash_combine(uint32 a, uint32 b)
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{
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a ^= b + 0x9e3779b9 + (a << 6) + (a >> 2);
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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 + UINT64CONST(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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* performance.
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*/
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static inline uint32
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murmurhash32(uint32 data)
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{
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uint32 h = data;
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h ^= h >> 16;
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h *= 0x85ebca6b;
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h ^= h >> 13;
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h *= 0xc2b2ae35;
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h ^= h >> 16;
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return h;
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}
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#endif /* HASHUTILS_H */
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