1 #ifndef _LINUX_JHASH_H
2 #define _LINUX_JHASH_H
3
4 /* jhash.h: Jenkins hash support.
5 *
6 * Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net)
7 *
8 * http://burtleburtle.net/bob/hash/
9 *
10 * These are the credits from Bob's sources:
11 *
12 * lookup2.c, by Bob Jenkins, December 1996, Public Domain.
13 * hash(), hash2(), hash3, and mix() are externally useful functions.
14 * Routines to test the hash are included if SELF_TEST is defined.
15 * You can use this free for any purpose. It has no warranty.
16 *
17 * Copyright (C) 2003 David S. Miller (davem@redhat.com)
18 *
19 * I've modified Bob's hash to be useful in the Linux kernel, and
20 * any bugs present are surely my fault. -DaveM
21 */
22
23 /* NOTE: Arguments are modified. */
24 #define __jhash_mix(a, b, c) \
25 { \
26 a -= b; a -= c; a ^= (c>>13); \
27 b -= c; b -= a; b ^= (a<<8); \
28 c -= a; c -= b; c ^= (b>>13); \
29 a -= b; a -= c; a ^= (c>>12); \
30 b -= c; b -= a; b ^= (a<<16); \
31 c -= a; c -= b; c ^= (b>>5); \
32 a -= b; a -= c; a ^= (c>>3); \
33 b -= c; b -= a; b ^= (a<<10); \
34 c -= a; c -= b; c ^= (b>>15); \
35 }
36
37 /* The golden ration: an arbitrary value */
38 #define JHASH_GOLDEN_RATIO 0x9e3779b9
39
40 /* The most generic version, hashes an arbitrary sequence
41 * of bytes. No alignment or length assumptions are made about
42 * the input key.
43 */
44 static inline u32 jhash(const void *key, u32 length, u32 initval)
45 {
46 u32 a, b, c, len;
47 const u8 *k = key;
48
49 len = length;
50 a = b = JHASH_GOLDEN_RATIO;
51 c = initval;
52
53 while (len >= 12) {
54 a += (k[0] +((u32)k[1]<<8) +((u32)k[2]<<16) +((u32)k[3]<<24));
55 b += (k[4] +((u32)k[5]<<8) +((u32)k[6]<<16) +((u32)k[7]<<24));
56 c += (k[8] +((u32)k[9]<<8) +((u32)k[10]<<16)+((u32)k[11]<<24));
57
58 __jhash_mix(a,b,c);
59
60 k += 12;
61 len -= 12;
62 }
63
64 c += length;
65 switch (len) {
66 case 11: c += ((u32)k[10]<<24);
67 case 10: c += ((u32)k[9]<<16);
68 case 9 : c += ((u32)k[8]<<8);
69 case 8 : b += ((u32)k[7]<<24);
70 case 7 : b += ((u32)k[6]<<16);
71 case 6 : b += ((u32)k[5]<<8);
72 case 5 : b += k[4];
73 case 4 : a += ((u32)k[3]<<24);
74 case 3 : a += ((u32)k[2]<<16);
75 case 2 : a += ((u32)k[1]<<8);
76 case 1 : a += k[0];
77 };
78
79 __jhash_mix(a,b,c);
80
81 return c;
82 }
83
84 /* A special optimized version that handles 1 or more of u32s.
85 * The length parameter here is the number of u32s in the key.
86 */
87 static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
88 {
89 u32 a, b, c, len;
90
91 a = b = JHASH_GOLDEN_RATIO;
92 c = initval;
93 len = length;
94
95 while (len >= 3) {
96 a += k[0];
97 b += k[1];
98 c += k[2];
99 __jhash_mix(a, b, c);
100 k += 3; len -= 3;
101 }
102
103 c += length * 4;
104
105 switch (len) {
106 case 2 : b += k[1];
107 case 1 : a += k[0];
108 };
109
110 __jhash_mix(a,b,c);
111
112 return c;
113 }
114
115
116 /* A special ultra-optimized versions that knows they are hashing exactly
117 * 3, 2 or 1 word(s).
118 *
119 * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
120 * done at the end is not done here.
121 */
122 static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
123 {
124 a += JHASH_GOLDEN_RATIO;
125 b += JHASH_GOLDEN_RATIO;
126 c += initval;
127
128 __jhash_mix(a, b, c);
129
130 return c;
131 }
132
133 static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
134 {
135 return jhash_3words(a, b, 0, initval);
136 }
137
138 static inline u32 jhash_1word(u32 a, u32 initval)
139 {
140 return jhash_3words(a, 0, 0, initval);
141 }
142
143 #endif /* _LINUX_JHASH_H */
144
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