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bdc7211e JA |
1 | #ifndef _LINUX_HASH_H |
2 | #define _LINUX_HASH_H | |
daaa166f | 3 | |
dadf66c5 | 4 | #include <inttypes.h> |
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 | ||
ed1860cd | 31 | static inline unsigned long __hash_long(unsigned long val) |
bdc7211e JA |
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 | ||
ed1860cd JA |
55 | return hash; |
56 | } | |
57 | ||
58 | static inline unsigned long hash_long(unsigned long val, unsigned int bits) | |
59 | { | |
bdc7211e | 60 | /* High bits are more random, so use them. */ |
ed1860cd | 61 | return __hash_long(val) >> (BITS_PER_LONG - bits); |
bdc7211e JA |
62 | } |
63 | ||
64 | static inline unsigned long hash_ptr(void *ptr, unsigned int bits) | |
65 | { | |
e43606c2 | 66 | return hash_long((uintptr_t)ptr, bits); |
bdc7211e | 67 | } |
dadf66c5 JA |
68 | |
69 | /* | |
70 | * Bob Jenkins jhash | |
71 | */ | |
72 | ||
73 | #define JHASH_INITVAL GOLDEN_RATIO_PRIME | |
74 | ||
75 | static inline uint32_t rol32(uint32_t word, uint32_t shift) | |
76 | { | |
77 | return (word << shift) | (word >> (32 - shift)); | |
78 | } | |
79 | ||
80 | /* __jhash_mix -- mix 3 32-bit values reversibly. */ | |
81 | #define __jhash_mix(a, b, c) \ | |
82 | { \ | |
83 | a -= c; a ^= rol32(c, 4); c += b; \ | |
84 | b -= a; b ^= rol32(a, 6); a += c; \ | |
85 | c -= b; c ^= rol32(b, 8); b += a; \ | |
86 | a -= c; a ^= rol32(c, 16); c += b; \ | |
87 | b -= a; b ^= rol32(a, 19); a += c; \ | |
88 | c -= b; c ^= rol32(b, 4); b += a; \ | |
89 | } | |
90 | ||
91 | /* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */ | |
92 | #define __jhash_final(a, b, c) \ | |
93 | { \ | |
94 | c ^= b; c -= rol32(b, 14); \ | |
95 | a ^= c; a -= rol32(c, 11); \ | |
96 | b ^= a; b -= rol32(a, 25); \ | |
97 | c ^= b; c -= rol32(b, 16); \ | |
98 | a ^= c; a -= rol32(c, 4); \ | |
99 | b ^= a; b -= rol32(a, 14); \ | |
100 | c ^= b; c -= rol32(b, 24); \ | |
101 | } | |
102 | ||
103 | static inline uint32_t jhash(const void *key, uint32_t length, uint32_t initval) | |
104 | { | |
105 | const uint8_t *k = key; | |
106 | uint32_t a, b, c; | |
107 | ||
108 | /* Set up the internal state */ | |
109 | a = b = c = JHASH_INITVAL + length + initval; | |
110 | ||
111 | /* All but the last block: affect some 32 bits of (a,b,c) */ | |
112 | while (length > 12) { | |
113 | a += *k; | |
114 | b += *(k + 4); | |
115 | c += *(k + 8); | |
116 | __jhash_mix(a, b, c); | |
117 | length -= 12; | |
118 | k += 12; | |
119 | } | |
120 | ||
121 | /* Last block: affect all 32 bits of (c) */ | |
122 | /* All the case statements fall through */ | |
123 | switch (length) { | |
124 | case 12: c += (uint32_t) k[11] << 24; | |
125 | case 11: c += (uint32_t) k[10] << 16; | |
126 | case 10: c += (uint32_t) k[9] << 8; | |
127 | case 9: c += k[8]; | |
128 | case 8: b += (uint32_t) k[7] << 24; | |
129 | case 7: b += (uint32_t) k[6] << 16; | |
130 | case 6: b += (uint32_t) k[5] << 8; | |
131 | case 5: b += k[4]; | |
132 | case 4: a += (uint32_t) k[3] << 24; | |
133 | case 3: a += (uint32_t) k[2] << 16; | |
134 | case 2: a += (uint32_t) k[1] << 8; | |
135 | case 1: a += k[0]; | |
136 | __jhash_final(a, b, c); | |
137 | case 0: /* Nothing left to add */ | |
138 | break; | |
139 | } | |
140 | ||
141 | return c; | |
142 | } | |
143 | ||
bdc7211e | 144 | #endif /* _LINUX_HASH_H */ |