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af38498d4c
... as well as its implementation from backend/access/hash/hashfunc.c to backend/utils/hash/hashfn.c. access/hash is the place for the hash index AM, not really appropriate for generic facilities, which is what hash_any is; having things the old way meant that anything using hash_any had to include the AM's include file, pointlessly polluting its namespace with unrelated, unnecessary cruft. Also move the HTEqual strategy number to access/stratnum.h from access/hash.h. To avoid breaking third-party extension code, add an #include "utils/hashutils.h" to access/hash.h. (An easily removed line by committers who enjoy their asbestos suits to protect them from angry extension authors.) Discussion: https://postgr.es/m/201901251935.ser5e4h6djt2@alvherre.pgsql
73 lines
1.8 KiB
C
73 lines
1.8 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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* Rotate the high 32 bits and the low 32 bits separately. The standard
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* hash function sometimes rotates the low 32 bits by one bit when
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* combining elements. We want extended hash functions to be compatible with
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* that algorithm when the seed is 0, so we can't just do a normal rotation.
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* This works, though.
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*/
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#define ROTATE_HIGH_AND_LOW_32BITS(v) \
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((((v) << 1) & UINT64CONST(0xfffffffefffffffe)) | \
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(((v) >> 31) & UINT64CONST(0x100000001)))
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extern Datum hash_any(register const unsigned char *k, register int keylen);
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extern Datum hash_any_extended(register const unsigned char *k,
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register int keylen, uint64 seed);
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extern Datum hash_uint32(uint32 k);
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extern Datum hash_uint32_extended(uint32 k, uint64 seed);
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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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