1 /*
2 * Utilities for working with hash values.
3 *
4 * Portions Copyright (c) 2017-2021, 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
hash_any(const unsigned char * k,int keylen)31 hash_any(const unsigned char *k, int keylen)
32 {
33 return UInt32GetDatum(hash_bytes(k, keylen));
34 }
35
36 static inline Datum
hash_any_extended(const unsigned char * k,int keylen,uint64 seed)37 hash_any_extended(const unsigned char *k, int keylen, uint64 seed)
38 {
39 return UInt64GetDatum(hash_bytes_extended(k, keylen, seed));
40 }
41
42 static inline Datum
hash_uint32(uint32 k)43 hash_uint32(uint32 k)
44 {
45 return UInt32GetDatum(hash_bytes_uint32(k));
46 }
47
48 static inline Datum
hash_uint32_extended(uint32 k,uint64 seed)49 hash_uint32_extended(uint32 k, uint64 seed)
50 {
51 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
hash_combine(uint32 a,uint32 b)68 hash_combine(uint32 a, uint32 b)
69 {
70 a ^= b + 0x9e3779b9 + (a << 6) + (a >> 2);
71 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
hash_combine64(uint64 a,uint64 b)80 hash_combine64(uint64 a, uint64 b)
81 {
82 /* 0x49a0f4dd15e5a8e3 is 64bit random data */
83 a ^= b + UINT64CONST(0x49a0f4dd15e5a8e3) + (a << 54) + (a >> 7);
84 return a;
85 }
86
87 /*
88 * Simple inline murmur hash implementation hashing a 32 bit integer, for
89 * performance.
90 */
91 static inline uint32
murmurhash32(uint32 data)92 murmurhash32(uint32 data)
93 {
94 uint32 h = data;
95
96 h ^= h >> 16;
97 h *= 0x85ebca6b;
98 h ^= h >> 13;
99 h *= 0xc2b2ae35;
100 h ^= h >> 16;
101 return h;
102 }
103
104 #endif /* HASHFN_H */
105