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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 | */ | |
8e87e014 | 87 | static inline u32 jhash2(const u32 *k, u32 length, u32 initval) |
1da177e4 LT |
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 */ |