libmarkers/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 #include "kernelcompat.h"
  24
  25 /* NOTE: Arguments are modified. */
  26 #define __jhash_mix(a, b, c) \
  27 { \
  28   a -= b; a -= c; a ^= (c>>13); \
  29   b -= c; b -= a; b ^= (a<<8); \
  30   c -= a; c -= b; c ^= (b>>13); \
  31   a -= b; a -= c; a ^= (c>>12);  \
  32   b -= c; b -= a; b ^= (a<<16); \
  33   c -= a; c -= b; c ^= (b>>5); \
  34   a -= b; a -= c; a ^= (c>>3);  \
  35   b -= c; b -= a; b ^= (a<<10); \
  36   c -= a; c -= b; c ^= (b>>15); \
  37 }
  38
  39 /* The golden ration: an arbitrary value */
  40 #define JHASH_GOLDEN_RATIO      0x9e3779b9
  41
  42 /* The most generic version, hashes an arbitrary sequence
  43  * of bytes.  No alignment or length assumptions are made about
  44  * the input key.
  45  */
  46 static inline u32 jhash(const void *key, u32 length, u32 initval)
  47 {
  48         u32 a, b, c, len;
  49         const u8 *k = key;
  50
  51         len = length;
  52         a = b = JHASH_GOLDEN_RATIO;
  53         c = initval;
  54
  55         while (len >= 12) {
  56                 a += (k[0] +((u32)k[1]<<8) +((u32)k[2]<<16) +((u32)k[3]<<24));
  57                 b += (k[4] +((u32)k[5]<<8) +((u32)k[6]<<16) +((u32)k[7]<<24));
  58                 c += (k[8] +((u32)k[9]<<8) +((u32)k[10]<<16)+((u32)k[11]<<24));
  59
  60                 __jhash_mix(a,b,c);
  61
  62                 k += 12;
  63                 len -= 12;
  64         }
  65
  66         c += length;
  67         switch (len) {
  68         case 11: c += ((u32)k[10]<<24);
  69         case 10: c += ((u32)k[9]<<16);
  70         case 9 : c += ((u32)k[8]<<8);
  71         case 8 : b += ((u32)k[7]<<24);
  72         case 7 : b += ((u32)k[6]<<16);
  73         case 6 : b += ((u32)k[5]<<8);
  74         case 5 : b += k[4];
  75         case 4 : a += ((u32)k[3]<<24);
  76         case 3 : a += ((u32)k[2]<<16);
  77         case 2 : a += ((u32)k[1]<<8);
  78         case 1 : a += k[0];
  79         };
  80
  81         __jhash_mix(a,b,c);
  82
  83         return c;
  84 }
  85
  86 /* A special optimized version that handles 1 or more of u32s.
  87  * The length parameter here is the number of u32s in the key.
  88  */
  89 static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
  90 {
  91         u32 a, b, c, len;
  92
  93         a = b = JHASH_GOLDEN_RATIO;
  94         c = initval;
  95         len = length;
  96
  97         while (len >= 3) {
  98                 a += k[0];
  99                 b += k[1];
 100                 c += k[2];
 101                 __jhash_mix(a, b, c);
 102                 k += 3; len -= 3;
 103         }
 104
 105         c += length * 4;
 106
 107         switch (len) {
 108         case 2 : b += k[1];
 109         case 1 : a += k[0];
 110         };
 111
 112         __jhash_mix(a,b,c);
 113
 114         return c;
 115 }
 116
 117
 118 /* A special ultra-optimized versions that knows they are hashing exactly
 119  * 3, 2 or 1 word(s).
 120  *
 121  * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
 122  *       done at the end is not done here.
 123  */
 124 static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
 125 {
 126         a += JHASH_GOLDEN_RATIO;
 127         b += JHASH_GOLDEN_RATIO;
 128         c += initval;
 129
 130         __jhash_mix(a, b, c);
 131
 132         return c;
 133 }
 134
 135 static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
 136 {
 137         return jhash_3words(a, b, 0, initval);
 138 }
 139
 140 static inline u32 jhash_1word(u32 a, u32 initval)
 141 {
 142         return jhash_3words(a, 0, 0, initval);
 143 }
 144
 145 #endif /* _LINUX_JHASH_H */