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 (at) 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 (at) 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 */ 158
