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1#ifndef _LINUX_HASH_H
2#define _LINUX_HASH_H
daaa166f 3
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5#include "arch/arch.h"
6
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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
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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
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31/*
32 * The above primes are actively bad for hashing, since they are
33 * too sparse. The 32-bit one is mostly ok, the 64-bit one causes
34 * real problems. Besides, the "prime" part is pointless for the
35 * multiplicative hash.
36 *
37 * Although a random odd number will do, it turns out that the golden
38 * ratio phi = (sqrt(5)-1)/2, or its negative, has particularly nice
39 * properties.
40 *
41 * These are the negative, (1 - phi) = (phi^2) = (3 - sqrt(5))/2.
42 * (See Knuth vol 3, section 6.4, exercise 9.)
43 */
44#define GOLDEN_RATIO_32 0x61C88647
45#define GOLDEN_RATIO_64 0x61C8864680B583EBull
a5a4fdfd 46
1bd4cb6b 47static inline unsigned long __hash_long(uint64_t val)
bdc7211e 48{
1bd4cb6b 49 uint64_t hash = val;
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50
51#if BITS_PER_LONG == 64
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52 hash *= GOLDEN_RATIO_64;
53#else
bdc7211e 54 /* Sigh, gcc can't optimise this alone like it does for 32 bits. */
1bd4cb6b 55 uint64_t n = hash;
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56 n <<= 18;
57 hash -= n;
58 n <<= 33;
59 hash -= n;
60 n <<= 3;
61 hash += n;
62 n <<= 3;
63 hash -= n;
64 n <<= 4;
65 hash += n;
66 n <<= 2;
67 hash += n;
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68#endif
69
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70 return hash;
71}
72
73static inline unsigned long hash_long(unsigned long val, unsigned int bits)
74{
bdc7211e 75 /* High bits are more random, so use them. */
ed1860cd 76 return __hash_long(val) >> (BITS_PER_LONG - bits);
bdc7211e 77}
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78
79static inline uint64_t __hash_u64(uint64_t val)
80{
2078c136 81 return val * GOLDEN_RATIO_64;
a5a4fdfd 82}
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83
84static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
85{
e43606c2 86 return hash_long((uintptr_t)ptr, bits);
bdc7211e 87}
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88
89/*
90 * Bob Jenkins jhash
91 */
92
2078c136 93#define JHASH_INITVAL GOLDEN_RATIO_32
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94
95static inline uint32_t rol32(uint32_t word, uint32_t shift)
96{
97 return (word << shift) | (word >> (32 - shift));
98}
99
100/* __jhash_mix -- mix 3 32-bit values reversibly. */
101#define __jhash_mix(a, b, c) \
102{ \
103 a -= c; a ^= rol32(c, 4); c += b; \
104 b -= a; b ^= rol32(a, 6); a += c; \
105 c -= b; c ^= rol32(b, 8); b += a; \
106 a -= c; a ^= rol32(c, 16); c += b; \
107 b -= a; b ^= rol32(a, 19); a += c; \
108 c -= b; c ^= rol32(b, 4); b += a; \
109}
110
111/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
112#define __jhash_final(a, b, c) \
113{ \
114 c ^= b; c -= rol32(b, 14); \
115 a ^= c; a -= rol32(c, 11); \
116 b ^= a; b -= rol32(a, 25); \
117 c ^= b; c -= rol32(b, 16); \
118 a ^= c; a -= rol32(c, 4); \
119 b ^= a; b -= rol32(a, 14); \
120 c ^= b; c -= rol32(b, 24); \
121}
122
123static inline uint32_t jhash(const void *key, uint32_t length, uint32_t initval)
124{
125 const uint8_t *k = key;
126 uint32_t a, b, c;
127
128 /* Set up the internal state */
129 a = b = c = JHASH_INITVAL + length + initval;
130
131 /* All but the last block: affect some 32 bits of (a,b,c) */
132 while (length > 12) {
133 a += *k;
134 b += *(k + 4);
135 c += *(k + 8);
136 __jhash_mix(a, b, c);
137 length -= 12;
138 k += 12;
139 }
140
141 /* Last block: affect all 32 bits of (c) */
142 /* All the case statements fall through */
143 switch (length) {
144 case 12: c += (uint32_t) k[11] << 24;
145 case 11: c += (uint32_t) k[10] << 16;
146 case 10: c += (uint32_t) k[9] << 8;
147 case 9: c += k[8];
148 case 8: b += (uint32_t) k[7] << 24;
149 case 7: b += (uint32_t) k[6] << 16;
150 case 6: b += (uint32_t) k[5] << 8;
151 case 5: b += k[4];
152 case 4: a += (uint32_t) k[3] << 24;
153 case 3: a += (uint32_t) k[2] << 16;
154 case 2: a += (uint32_t) k[1] << 8;
155 case 1: a += k[0];
156 __jhash_final(a, b, c);
157 case 0: /* Nothing left to add */
158 break;
159 }
160
161 return c;
162}
163
bdc7211e 164#endif /* _LINUX_HASH_H */