120 lines
2.7 KiB
C
120 lines
2.7 KiB
C
/*
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* Utilities for working with hash values.
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*
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* Portions Copyright (c) 2017-2024, PostgreSQL Global Development Group
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*/
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#ifndef HASHFN_H
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#define HASHFN_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 uint32 hash_bytes(const unsigned char *k, int keylen);
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extern uint64 hash_bytes_extended(const unsigned char *k,
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int keylen, uint64 seed);
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extern uint32 hash_bytes_uint32(uint32 k);
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extern uint64 hash_bytes_uint32_extended(uint32 k, uint64 seed);
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#ifndef FRONTEND
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static inline Datum
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hash_any(const unsigned char *k, int keylen)
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{
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return UInt32GetDatum(hash_bytes(k, keylen));
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}
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static inline Datum
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hash_any_extended(const unsigned char *k, int keylen, uint64 seed)
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{
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return UInt64GetDatum(hash_bytes_extended(k, keylen, seed));
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}
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static inline Datum
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hash_uint32(uint32 k)
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{
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return UInt32GetDatum(hash_bytes_uint32(k));
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}
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static inline Datum
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hash_uint32_extended(uint32 k, uint64 seed)
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{
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return UInt64GetDatum(hash_bytes_uint32_extended(k, seed));
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}
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#endif
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extern uint32 string_hash(const void *key, Size keysize);
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extern uint32 tag_hash(const void *key, Size keysize);
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extern uint32 uint32_hash(const void *key, Size keysize);
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#define oid_hash uint32_hash /* Remove me eventually */
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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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/* 64-bit variant */
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static inline uint64
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murmurhash64(uint64 data)
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{
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uint64 h = data;
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h ^= h >> 33;
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h *= 0xff51afd7ed558ccd;
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h ^= h >> 33;
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h *= 0xc4ceb9fe1a85ec53;
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h ^= h >> 33;
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return h;
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}
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#endif /* HASHFN_H */
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