include/linux/jhash.h

   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 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 */