2 * Utilities for working with hash values.
4 * Portions Copyright (c) 2017-2019, PostgreSQL Global Development Group
12 * Rotate the high 32 bits and the low 32 bits separately. The standard
13 * hash function sometimes rotates the low 32 bits by one bit when
14 * combining elements. We want extended hash functions to be compatible with
15 * that algorithm when the seed is 0, so we can't just do a normal rotation.
18 #define ROTATE_HIGH_AND_LOW_32BITS(v) \
19 ((((v) << 1) & UINT64CONST(0xfffffffefffffffe)) | \
20 (((v) >> 31) & UINT64CONST(0x100000001)))
23 extern Datum hash_any(const unsigned char *k, int keylen);
24 extern Datum hash_any_extended(const unsigned char *k,
25 int keylen, uint64 seed);
26 extern Datum hash_uint32(uint32 k);
27 extern Datum hash_uint32_extended(uint32 k, uint64 seed);
30 * Combine two 32-bit hash values, resulting in another hash value, with
33 * Similar to boost's hash_combine().
36 hash_combine(uint32 a, uint32 b)
38 a ^= b + 0x9e3779b9 + (a << 6) + (a >> 2);
43 * Combine two 64-bit hash values, resulting in another hash value, using the
44 * same kind of technique as hash_combine(). Testing shows that this also
45 * produces good bit mixing.
48 hash_combine64(uint64 a, uint64 b)
50 /* 0x49a0f4dd15e5a8e3 is 64bit random data */
51 a ^= b + UINT64CONST(0x49a0f4dd15e5a8e3) + (a << 54) + (a >> 7);
56 * Simple inline murmur hash implementation hashing a 32 bit integer, for
60 murmurhash32(uint32 data)
72 #endif /* HASHUTILS_H */