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1#ifndef _LINUX_HASH_H
2#define _LINUX_HASH_H
3
4#include <inttypes.h>
5#include "arch/arch.h"
6#include "compiler/compiler.h"
7
8/* Fast hashing routine for a long.
9 (C) 2002 William Lee Irwin III, IBM */
10
11/*
12 * Knuth recommends primes in approximately golden ratio to the maximum
13 * integer representable by a machine word for multiplicative hashing.
14 * Chuck Lever verified the effectiveness of this technique:
15 * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
16 *
17 * These primes are chosen to be bit-sparse, that is operations on
18 * them can use shifts and additions instead of multiplications for
19 * machines where multiplications are slow.
20 */
21
22#if BITS_PER_LONG == 32
23/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
24#define GOLDEN_RATIO_PRIME 0x9e370001UL
25#elif BITS_PER_LONG == 64
26/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
27#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL
28#else
29#error Define GOLDEN_RATIO_PRIME for your wordsize.
30#endif
31
32/*
33 * The above primes are actively bad for hashing, since they are
34 * too sparse. The 32-bit one is mostly ok, the 64-bit one causes
35 * real problems. Besides, the "prime" part is pointless for the
36 * multiplicative hash.
37 *
38 * Although a random odd number will do, it turns out that the golden
39 * ratio phi = (sqrt(5)-1)/2, or its negative, has particularly nice
40 * properties.
41 *
42 * These are the negative, (1 - phi) = (phi^2) = (3 - sqrt(5))/2.
43 * (See Knuth vol 3, section 6.4, exercise 9.)
44 */
45#define GOLDEN_RATIO_32 0x61C88647
46#define GOLDEN_RATIO_64 0x61C8864680B583EBull
47
48static inline unsigned long __hash_long(uint64_t val)
49{
50 uint64_t hash = val;
51
52#if BITS_PER_LONG == 64
53 hash *= GOLDEN_RATIO_64;
54#else
55 /* Sigh, gcc can't optimise this alone like it does for 32 bits. */
56 uint64_t n = hash;
57 n <<= 18;
58 hash -= n;
59 n <<= 33;
60 hash -= n;
61 n <<= 3;
62 hash += n;
63 n <<= 3;
64 hash -= n;
65 n <<= 4;
66 hash += n;
67 n <<= 2;
68 hash += n;
69#endif
70
71 return hash;
72}
73
74static inline unsigned long hash_long(unsigned long val, unsigned int bits)
75{
76 /* High bits are more random, so use them. */
77 return __hash_long(val) >> (BITS_PER_LONG - bits);
78}
79
80static inline uint64_t __hash_u64(uint64_t val)
81{
82 return val * GOLDEN_RATIO_64;
83}
84
85static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
86{
87 return hash_long((uintptr_t)ptr, bits);
88}
89
90/*
91 * Bob Jenkins jhash
92 */
93
94#define JHASH_INITVAL GOLDEN_RATIO_32
95
96static inline uint32_t rol32(uint32_t word, uint32_t shift)
97{
98 return (word << shift) | (word >> (32 - shift));
99}
100
101/* __jhash_mix -- mix 3 32-bit values reversibly. */
102#define __jhash_mix(a, b, c) \
103{ \
104 a -= c; a ^= rol32(c, 4); c += b; \
105 b -= a; b ^= rol32(a, 6); a += c; \
106 c -= b; c ^= rol32(b, 8); b += a; \
107 a -= c; a ^= rol32(c, 16); c += b; \
108 b -= a; b ^= rol32(a, 19); a += c; \
109 c -= b; c ^= rol32(b, 4); b += a; \
110}
111
112/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
113#define __jhash_final(a, b, c) \
114{ \
115 c ^= b; c -= rol32(b, 14); \
116 a ^= c; a -= rol32(c, 11); \
117 b ^= a; b -= rol32(a, 25); \
118 c ^= b; c -= rol32(b, 16); \
119 a ^= c; a -= rol32(c, 4); \
120 b ^= a; b -= rol32(a, 14); \
121 c ^= b; c -= rol32(b, 24); \
122}
123
124static inline uint32_t jhash(const void *key, uint32_t length, uint32_t initval)
125{
126 const uint8_t *k = key;
127 uint32_t a, b, c;
128
129 /* Set up the internal state */
130 a = b = c = JHASH_INITVAL + length + initval;
131
132 /* All but the last block: affect some 32 bits of (a,b,c) */
133 while (length > 12) {
134 a += *k;
135 b += *(k + 4);
136 c += *(k + 8);
137 __jhash_mix(a, b, c);
138 length -= 12;
139 k += 12;
140 }
141
142 /* Last block: affect all 32 bits of (c) */
143 /* All the case statements fall through */
144 switch (length) {
145 case 12: c += (uint32_t) k[11] << 24; fallthrough;
146 case 11: c += (uint32_t) k[10] << 16; fallthrough;
147 case 10: c += (uint32_t) k[9] << 8; fallthrough;
148 case 9: c += k[8]; fallthrough;
149 case 8: b += (uint32_t) k[7] << 24; fallthrough;
150 case 7: b += (uint32_t) k[6] << 16; fallthrough;
151 case 6: b += (uint32_t) k[5] << 8; fallthrough;
152 case 5: b += k[4]; fallthrough;
153 case 4: a += (uint32_t) k[3] << 24; fallthrough;
154 case 3: a += (uint32_t) k[2] << 16; fallthrough;
155 case 2: a += (uint32_t) k[1] << 8; fallthrough;
156 case 1: a += k[0];
157 __jhash_final(a, b, c);
158 fallthrough;
159 case 0: /* Nothing left to add */
160 break;
161 }
162
163 return c;
164}
165
166#endif /* _LINUX_HASH_H */