| 1 | #ifndef _LINUX_JHASH_H |
| 2 | #define _LINUX_JHASH_H |
| 3 | |
| 4 | /* jhash.h: Jenkins hash support. |
| 5 | * |
| 6 | * Copyright (C) 2006. 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 | * lookup3.c, by Bob Jenkins, May 2006, Public Domain. |
| 13 | * |
| 14 | * These are functions for producing 32-bit hashes for hash table lookup. |
| 15 | * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final() |
| 16 | * are externally useful functions. Routines to test the hash are included |
| 17 | * if SELF_TEST is defined. You can use this free for any purpose. It's in |
| 18 | * the public domain. It has no warranty. |
| 19 | * |
| 20 | * Copyright (C) 2009 Jozsef Kadlecsik (kadlec@blackhole.kfki.hu) |
| 21 | * |
| 22 | * I've modified Bob's hash to be useful in the Linux kernel, and |
| 23 | * any bugs present are my fault. Jozsef |
| 24 | */ |
| 25 | |
| 26 | #define __rot(x,k) (((x)<<(k)) | ((x)>>(32-(k)))) |
| 27 | |
| 28 | /* __jhash_mix - mix 3 32-bit values reversibly. */ |
| 29 | #define __jhash_mix(a,b,c) \ |
| 30 | { \ |
| 31 | a -= c; a ^= __rot(c, 4); c += b; \ |
| 32 | b -= a; b ^= __rot(a, 6); a += c; \ |
| 33 | c -= b; c ^= __rot(b, 8); b += a; \ |
| 34 | a -= c; a ^= __rot(c,16); c += b; \ |
| 35 | b -= a; b ^= __rot(a,19); a += c; \ |
| 36 | c -= b; c ^= __rot(b, 4); b += a; \ |
| 37 | } |
| 38 | |
| 39 | /* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */ |
| 40 | #define __jhash_final(a,b,c) \ |
| 41 | { \ |
| 42 | c ^= b; c -= __rot(b,14); \ |
| 43 | a ^= c; a -= __rot(c,11); \ |
| 44 | b ^= a; b -= __rot(a,25); \ |
| 45 | c ^= b; c -= __rot(b,16); \ |
| 46 | a ^= c; a -= __rot(c,4); \ |
| 47 | b ^= a; b -= __rot(a,14); \ |
| 48 | c ^= b; c -= __rot(b,24); \ |
| 49 | } |
| 50 | |
| 51 | /* The golden ration: an arbitrary value */ |
| 52 | #define JHASH_GOLDEN_RATIO 0xdeadbeef |
| 53 | |
| 54 | /* The most generic version, hashes an arbitrary sequence |
| 55 | * of bytes. No alignment or length assumptions are made about |
| 56 | * the input key. The result depends on endianness. |
| 57 | */ |
| 58 | static inline u32 jhash(const void *key, u32 length, u32 initval) |
| 59 | { |
| 60 | u32 a,b,c; |
| 61 | const u8 *k = key; |
| 62 | |
| 63 | /* Set up the internal state */ |
| 64 | a = b = c = JHASH_GOLDEN_RATIO + length + initval; |
| 65 | |
| 66 | /* all but the last block: affect some 32 bits of (a,b,c) */ |
| 67 | while (length > 12) { |
| 68 | a += (k[0] + ((u32)k[1]<<8) + ((u32)k[2]<<16) + ((u32)k[3]<<24)); |
| 69 | b += (k[4] + ((u32)k[5]<<8) + ((u32)k[6]<<16) + ((u32)k[7]<<24)); |
| 70 | c += (k[8] + ((u32)k[9]<<8) + ((u32)k[10]<<16) + ((u32)k[11]<<24)); |
| 71 | __jhash_mix(a, b, c); |
| 72 | length -= 12; |
| 73 | k += 12; |
| 74 | } |
| 75 | |
| 76 | /* last block: affect all 32 bits of (c) */ |
| 77 | /* all the case statements fall through */ |
| 78 | switch (length) { |
| 79 | case 12: c += (u32)k[11]<<24; |
| 80 | case 11: c += (u32)k[10]<<16; |
| 81 | case 10: c += (u32)k[9]<<8; |
| 82 | case 9 : c += k[8]; |
| 83 | case 8 : b += (u32)k[7]<<24; |
| 84 | case 7 : b += (u32)k[6]<<16; |
| 85 | case 6 : b += (u32)k[5]<<8; |
| 86 | case 5 : b += k[4]; |
| 87 | case 4 : a += (u32)k[3]<<24; |
| 88 | case 3 : a += (u32)k[2]<<16; |
| 89 | case 2 : a += (u32)k[1]<<8; |
| 90 | case 1 : a += k[0]; |
| 91 | __jhash_final(a, b, c); |
| 92 | case 0 : |
| 93 | break; |
| 94 | } |
| 95 | |
| 96 | return c; |
| 97 | } |
| 98 | |
| 99 | /* A special optimized version that handles 1 or more of u32s. |
| 100 | * The length parameter here is the number of u32s in the key. |
| 101 | */ |
| 102 | static inline u32 jhash2(u32 *k, u32 length, u32 initval) |
| 103 | { |
| 104 | u32 a, b, c; |
| 105 | |
| 106 | /* Set up the internal state */ |
| 107 | a = b = c = JHASH_GOLDEN_RATIO + (length<<2) + initval; |
| 108 | |
| 109 | /* handle most of the key */ |
| 110 | while (length > 3) { |
| 111 | a += k[0]; |
| 112 | b += k[1]; |
| 113 | c += k[2]; |
| 114 | __jhash_mix(a, b, c); |
| 115 | length -= 3; |
| 116 | k += 3; |
| 117 | } |
| 118 | |
| 119 | /* handle the last 3 u32's */ |
| 120 | /* all the case statements fall through */ |
| 121 | switch (length) { |
| 122 | case 3: c += k[2]; |
| 123 | case 2: b += k[1]; |
| 124 | case 1: a += k[0]; |
| 125 | __jhash_final(a, b, c); |
| 126 | case 0: /* case 0: nothing left to add */ |
| 127 | break; |
| 128 | } |
| 129 | |
| 130 | return c; |
| 131 | } |
| 132 | |
| 133 | /* A special ultra-optimized versions that knows they are hashing exactly |
| 134 | * 3, 2 or 1 word(s). |
| 135 | */ |
| 136 | static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval) |
| 137 | { |
| 138 | a += JHASH_GOLDEN_RATIO + initval; |
| 139 | b += JHASH_GOLDEN_RATIO + initval; |
| 140 | c += JHASH_GOLDEN_RATIO + initval; |
| 141 | |
| 142 | __jhash_final(a, b, c); |
| 143 | |
| 144 | return c; |
| 145 | } |
| 146 | |
| 147 | static inline u32 jhash_2words(u32 a, u32 b, u32 initval) |
| 148 | { |
| 149 | return jhash_3words(0, a, b, initval); |
| 150 | } |
| 151 | |
| 152 | static inline u32 jhash_1word(u32 a, u32 initval) |
| 153 | { |
| 154 | return jhash_3words(0, 0, a, initval); |
| 155 | } |
| 156 | |
| 157 | #endif /* _LINUX_JHASH_H */ |