jhash.h (4569B)
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 * https://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) 2009-2010 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. 24 * Jozsef 25 */ 26#include <linux/bitops.h> 27#include <linux/unaligned/packed_struct.h> 28 29/* Best hash sizes are of power of two */ 30#define jhash_size(n) ((u32)1<<(n)) 31/* Mask the hash value, i.e (value & jhash_mask(n)) instead of (value % n) */ 32#define jhash_mask(n) (jhash_size(n)-1) 33 34/* __jhash_mix -- mix 3 32-bit values reversibly. */ 35#define __jhash_mix(a, b, c) \ 36{ \ 37 a -= c; a ^= rol32(c, 4); c += b; \ 38 b -= a; b ^= rol32(a, 6); a += c; \ 39 c -= b; c ^= rol32(b, 8); b += a; \ 40 a -= c; a ^= rol32(c, 16); c += b; \ 41 b -= a; b ^= rol32(a, 19); a += c; \ 42 c -= b; c ^= rol32(b, 4); b += a; \ 43} 44 45/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */ 46#define __jhash_final(a, b, c) \ 47{ \ 48 c ^= b; c -= rol32(b, 14); \ 49 a ^= c; a -= rol32(c, 11); \ 50 b ^= a; b -= rol32(a, 25); \ 51 c ^= b; c -= rol32(b, 16); \ 52 a ^= c; a -= rol32(c, 4); \ 53 b ^= a; b -= rol32(a, 14); \ 54 c ^= b; c -= rol32(b, 24); \ 55} 56 57/* An arbitrary initial parameter */ 58#define JHASH_INITVAL 0xdeadbeef 59 60/* jhash - hash an arbitrary key 61 * @k: sequence of bytes as key 62 * @length: the length of the key 63 * @initval: the previous hash, or an arbitray value 64 * 65 * The generic version, hashes an arbitrary sequence of bytes. 66 * No alignment or length assumptions are made about the input key. 67 * 68 * Returns the hash value of the key. The result depends on endianness. 69 */ 70static inline u32 jhash(const void *key, u32 length, u32 initval) 71{ 72 u32 a, b, c; 73 const u8 *k = key; 74 75 /* Set up the internal state */ 76 a = b = c = JHASH_INITVAL + length + initval; 77 78 /* All but the last block: affect some 32 bits of (a,b,c) */ 79 while (length > 12) { 80 a += __get_unaligned_cpu32(k); 81 b += __get_unaligned_cpu32(k + 4); 82 c += __get_unaligned_cpu32(k + 8); 83 __jhash_mix(a, b, c); 84 length -= 12; 85 k += 12; 86 } 87 /* Last block: affect all 32 bits of (c) */ 88 /* All the case statements fall through */ 89 switch (length) { 90 case 12: c += (u32)k[11]<<24; 91 case 11: c += (u32)k[10]<<16; 92 case 10: c += (u32)k[9]<<8; 93 case 9: c += k[8]; 94 case 8: b += (u32)k[7]<<24; 95 case 7: b += (u32)k[6]<<16; 96 case 6: b += (u32)k[5]<<8; 97 case 5: b += k[4]; 98 case 4: a += (u32)k[3]<<24; 99 case 3: a += (u32)k[2]<<16; 100 case 2: a += (u32)k[1]<<8; 101 case 1: a += k[0]; 102 __jhash_final(a, b, c); 103 case 0: /* Nothing left to add */ 104 break; 105 } 106 107 return c; 108} 109 110/* jhash2 - hash an array of u32's 111 * @k: the key which must be an array of u32's 112 * @length: the number of u32's in the key 113 * @initval: the previous hash, or an arbitray value 114 * 115 * Returns the hash value of the key. 116 */ 117static inline u32 jhash2(const u32 *k, u32 length, u32 initval) 118{ 119 u32 a, b, c; 120 121 /* Set up the internal state */ 122 a = b = c = JHASH_INITVAL + (length<<2) + initval; 123 124 /* Handle most of the key */ 125 while (length > 3) { 126 a += k[0]; 127 b += k[1]; 128 c += k[2]; 129 __jhash_mix(a, b, c); 130 length -= 3; 131 k += 3; 132 } 133 134 /* Handle the last 3 u32's: all the case statements fall through */ 135 switch (length) { 136 case 3: c += k[2]; 137 case 2: b += k[1]; 138 case 1: a += k[0]; 139 __jhash_final(a, b, c); 140 case 0: /* Nothing left to add */ 141 break; 142 } 143 144 return c; 145} 146 147 148/* __jhash_nwords - hash exactly 3, 2 or 1 word(s) */ 149static inline u32 __jhash_nwords(u32 a, u32 b, u32 c, u32 initval) 150{ 151 a += initval; 152 b += initval; 153 c += initval; 154 155 __jhash_final(a, b, c); 156 157 return c; 158} 159 160static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval) 161{ 162 return __jhash_nwords(a, b, c, initval + JHASH_INITVAL + (3 << 2)); 163} 164 165static inline u32 jhash_2words(u32 a, u32 b, u32 initval) 166{ 167 return __jhash_nwords(a, b, 0, initval + JHASH_INITVAL + (2 << 2)); 168} 169 170static inline u32 jhash_1word(u32 a, u32 initval) 171{ 172 return __jhash_nwords(a, 0, 0, initval + JHASH_INITVAL + (1 << 2)); 173} 174 175#endif /* _LINUX_JHASH_H */