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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 | */ |
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 particular 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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