CommitLineData
bdc7211e
JA
1#ifndef _LINUX_HASH_H
2#define _LINUX_HASH_H
daaa166f 3
daaa166f
JA
5#include "arch/arch.h"
6
bdc7211e
JA
7/* Fast hashing routine for a long.
8 (C) 2002 William Lee Irwin III, IBM */
9
10/*
11 * Knuth recommends primes in approximately golden ratio to the maximum
12 * integer representable by a machine word for multiplicative hashing.
13 * Chuck Lever verified the effectiveness of this technique:
14 * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
15 *
16 * These primes are chosen to be bit-sparse, that is operations on
17 * them can use shifts and additions instead of multiplications for
18 * machines where multiplications are slow.
19 */
5921e80c 20
bdc7211e
JA
21#if BITS_PER_LONG == 32
22/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
23#define GOLDEN_RATIO_PRIME 0x9e370001UL
24#elif BITS_PER_LONG == 64
25/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
26#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL
27#else
28#error Define GOLDEN_RATIO_PRIME for your wordsize.
29#endif
30
31static inline unsigned long hash_long(unsigned long val, unsigned int bits)
32{
33 unsigned long hash = val;
34
35#if BITS_PER_LONG == 64
36 /* Sigh, gcc can't optimise this alone like it does for 32 bits. */
37 unsigned long n = hash;
38 n <<= 18;
39 hash -= n;
40 n <<= 33;
41 hash -= n;
42 n <<= 3;
43 hash += n;
44 n <<= 3;
45 hash -= n;
46 n <<= 4;
47 hash += n;
48 n <<= 2;
49 hash += n;
50#else
51 /* On some cpus multiply is faster, on others gcc will do shifts */
52 hash *= GOLDEN_RATIO_PRIME;
53#endif
54
55 /* High bits are more random, so use them. */
56 return hash >> (BITS_PER_LONG - bits);
57}
58
59static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
60{
e43606c2 61 return hash_long((uintptr_t)ptr, bits);
bdc7211e 62}
JA
63
64/*
65 * Bob Jenkins jhash
66 */
67
68#define JHASH_INITVAL GOLDEN_RATIO_PRIME
69
70static inline uint32_t rol32(uint32_t word, uint32_t shift)
71{
72 return (word << shift) | (word >> (32 - shift));
73}
74
75/* __jhash_mix -- mix 3 32-bit values reversibly. */
76#define __jhash_mix(a, b, c) \
77{ \
78 a -= c; a ^= rol32(c, 4); c += b; \
79 b -= a; b ^= rol32(a, 6); a += c; \
80 c -= b; c ^= rol32(b, 8); b += a; \
81 a -= c; a ^= rol32(c, 16); c += b; \
82 b -= a; b ^= rol32(a, 19); a += c; \
83 c -= b; c ^= rol32(b, 4); b += a; \
84}
85
86/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
87#define __jhash_final(a, b, c) \
88{ \
89 c ^= b; c -= rol32(b, 14); \
90 a ^= c; a -= rol32(c, 11); \
91 b ^= a; b -= rol32(a, 25); \
92 c ^= b; c -= rol32(b, 16); \
93 a ^= c; a -= rol32(c, 4); \
94 b ^= a; b -= rol32(a, 14); \
95 c ^= b; c -= rol32(b, 24); \
96}
97
98static inline uint32_t jhash(const void *key, uint32_t length, uint32_t initval)
99{
100 const uint8_t *k = key;
101 uint32_t a, b, c;
102
103 /* Set up the internal state */
104 a = b = c = JHASH_INITVAL + length + initval;
105
106 /* All but the last block: affect some 32 bits of (a,b,c) */
107 while (length > 12) {
108 a += *k;
109 b += *(k + 4);
110 c += *(k + 8);
111 __jhash_mix(a, b, c);
112 length -= 12;
113 k += 12;
114 }
115
116 /* Last block: affect all 32 bits of (c) */
117 /* All the case statements fall through */
118 switch (length) {
119 case 12: c += (uint32_t) k[11] << 24;
120 case 11: c += (uint32_t) k[10] << 16;
121 case 10: c += (uint32_t) k[9] << 8;
122 case 9: c += k[8];
123 case 8: b += (uint32_t) k[7] << 24;
124 case 7: b += (uint32_t) k[6] << 16;
125 case 6: b += (uint32_t) k[5] << 8;
126 case 5: b += k[4];
127 case 4: a += (uint32_t) k[3] << 24;
128 case 3: a += (uint32_t) k[2] << 16;
129 case 2: a += (uint32_t) k[1] << 8;
130 case 1: a += k[0];
131 __jhash_final(a, b, c);
132 case 0: /* Nothing left to add */
133 break;
134 }
135
136 return c;
137}
138
bdc7211e 139#endif /* _LINUX_HASH_H */