1 #ifndef _LINUX_HASH_H
2 #define _LINUX_HASH_H
3
4 #include <inttypes.h>
5 #include "arch/arch.h"
6
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 */
20
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
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
46
__hash_long(uint64_t val)47 static inline unsigned long __hash_long(uint64_t val)
48 {
49 uint64_t hash = val;
50
51 #if BITS_PER_LONG == 64
52 hash *= GOLDEN_RATIO_64;
53 #else
54 /* Sigh, gcc can't optimise this alone like it does for 32 bits. */
55 uint64_t n = hash;
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;
68 #endif
69
70 return hash;
71 }
72
hash_long(unsigned long val,unsigned int bits)73 static inline unsigned long hash_long(unsigned long val, unsigned int bits)
74 {
75 /* High bits are more random, so use them. */
76 return __hash_long(val) >> (BITS_PER_LONG - bits);
77 }
78
__hash_u64(uint64_t val)79 static inline uint64_t __hash_u64(uint64_t val)
80 {
81 return val * GOLDEN_RATIO_64;
82 }
83
hash_ptr(void * ptr,unsigned int bits)84 static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
85 {
86 return hash_long((uintptr_t)ptr, bits);
87 }
88
89 /*
90 * Bob Jenkins jhash
91 */
92
93 #define JHASH_INITVAL GOLDEN_RATIO_32
94
rol32(uint32_t word,uint32_t shift)95 static 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
jhash(const void * key,uint32_t length,uint32_t initval)123 static 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
164 #endif /* _LINUX_HASH_H */
165