Age Owner TLA Line data Source code
1 : /*
2 : * Utilities for working with hash values.
3 : *
4 : * Portions Copyright (c) 2017-2023, PostgreSQL Global Development Group
5 : */
6 :
7 : #ifndef HASHFN_H
8 : #define HASHFN_H
9 :
10 :
11 : /*
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.
16 : * This works, though.
17 : */
18 : #define ROTATE_HIGH_AND_LOW_32BITS(v) \
19 : ((((v) << 1) & UINT64CONST(0xfffffffefffffffe)) | \
20 : (((v) >> 31) & UINT64CONST(0x100000001)))
21 :
22 :
23 : extern uint32 hash_bytes(const unsigned char *k, int keylen);
24 : extern uint64 hash_bytes_extended(const unsigned char *k,
25 : int keylen, uint64 seed);
26 : extern uint32 hash_bytes_uint32(uint32 k);
27 : extern uint64 hash_bytes_uint32_extended(uint32 k, uint64 seed);
28 :
29 : #ifndef FRONTEND
30 : static inline Datum
1140 rhaas 31 CBC 12179183 : hash_any(const unsigned char *k, int keylen)
32 : {
33 12179183 : return UInt32GetDatum(hash_bytes(k, keylen));
34 : }
35 :
36 : static inline Datum
37 2563029 : hash_any_extended(const unsigned char *k, int keylen, uint64 seed)
38 : {
39 2563029 : return UInt64GetDatum(hash_bytes_extended(k, keylen, seed));
40 : }
41 :
42 : static inline Datum
43 27653513 : hash_uint32(uint32 k)
44 : {
45 27653513 : return UInt32GetDatum(hash_bytes_uint32(k));
46 : }
47 :
48 : static inline Datum
49 106947 : hash_uint32_extended(uint32 k, uint64 seed)
50 : {
51 106947 : return UInt64GetDatum(hash_bytes_uint32_extended(k, seed));
52 : }
53 : #endif
54 :
55 : extern uint32 string_hash(const void *key, Size keysize);
56 : extern uint32 tag_hash(const void *key, Size keysize);
57 : extern uint32 uint32_hash(const void *key, Size keysize);
58 :
59 : #define oid_hash uint32_hash /* Remove me eventually */
60 :
61 : /*
62 : * Combine two 32-bit hash values, resulting in another hash value, with
63 : * decent bit mixing.
64 : *
65 : * Similar to boost's hash_combine().
66 : */
67 : static inline uint32
2056 andres 68 12984643 : hash_combine(uint32 a, uint32 b)
69 : {
70 12984643 : a ^= b + 0x9e3779b9 + (a << 6) + (a >> 2);
71 12984643 : return a;
72 : }
73 :
74 : /*
75 : * Combine two 64-bit hash values, resulting in another hash value, using the
76 : * same kind of technique as hash_combine(). Testing shows that this also
77 : * produces good bit mixing.
78 : */
79 : static inline uint64
1988 rhaas 80 108462 : hash_combine64(uint64 a, uint64 b)
81 : {
82 : /* 0x49a0f4dd15e5a8e3 is 64bit random data */
1979 tgl 83 108462 : a ^= b + UINT64CONST(0x49a0f4dd15e5a8e3) + (a << 54) + (a >> 7);
1988 rhaas 84 108462 : return a;
85 : }
86 :
87 : /*
88 : * Simple inline murmur hash implementation hashing a 32 bit integer, for
89 : * performance.
90 : */
91 : static inline uint32
2025 andres 92 103423363 : murmurhash32(uint32 data)
93 : {
94 103423363 : uint32 h = data;
95 :
96 103423363 : h ^= h >> 16;
97 103423363 : h *= 0x85ebca6b;
98 103423363 : h ^= h >> 13;
99 103423363 : h *= 0xc2b2ae35;
100 103423363 : h ^= h >> 16;
101 103423363 : return h;
102 : }
103 :
104 : #endif /* HASHFN_H */
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