lib/jhash.c

   1 /* jhash.h: Jenkins hash support.
   2  *
   3  * Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net)
   4  *
   5  * http://burtleburtle.net/bob/hash/
   6  *
   7  * These are the credits from Bob's sources:
   8  *
   9  * lookup2.c, by Bob Jenkins, December 1996, Public Domain.
  10  * hash(), hash2(), hash3, and mix() are externally useful functions.
  11  * Routines to test the hash are included if SELF_TEST is defined.
  12  * You can use this free for any purpose.  It has no warranty.
  13  *
  14  * Copyright (C) 2003 David S. Miller (davem@redhat.com)
  15  *
  16  * I've modified Bob's hash to be useful in the Linux kernel, and
  17  * any bugs present are surely my fault.  -DaveM
  18  */
  19
  20 #include "zebra.h"
  21 #include "jhash.h"
  22
  23 /* The golden ration: an arbitrary value */
  24 #define JHASH_GOLDEN_RATIO  0x9e3779b9
  25
  26 /* NOTE: Arguments are modified. */
  27 #define __jhash_mix(a, b, c) \
  28 { \
  29   a -= b; a -= c; a ^= (c>>13); \
  30   b -= c; b -= a; b ^= (a<<8); \
  31   c -= a; c -= b; c ^= (b>>13); \
  32   a -= b; a -= c; a ^= (c>>12);  \
  33   b -= c; b -= a; b ^= (a<<16); \
  34   c -= a; c -= b; c ^= (b>>5); \
  35   a -= b; a -= c; a ^= (c>>3);  \
  36   b -= c; b -= a; b ^= (a<<10); \
  37   c -= a; c -= b; c ^= (b>>15); \
  38 }
  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 u_int32_t
  45 jhash (void *key, u_int32_t length, u_int32_t initval)
  46 {
  47   u_int32_t a, b, c, len;
  48   u_int8_t *k = key;
  49
  50   len = length;
  51   a = b = JHASH_GOLDEN_RATIO;
  52   c = initval;
  53
  54   while (len >= 12)
  55     {
  56       a +=
  57         (k[0] + ((u_int32_t) k[1] << 8) + ((u_int32_t) k[2] << 16) +
  58          ((u_int32_t) k[3] << 24));
  59       b +=
  60         (k[4] + ((u_int32_t) k[5] << 8) + ((u_int32_t) k[6] << 16) +
  61          ((u_int32_t) k[7] << 24));
  62       c +=
  63         (k[8] + ((u_int32_t) k[9] << 8) + ((u_int32_t) k[10] << 16) +
  64          ((u_int32_t) k[11] << 24));
  65
  66       __jhash_mix (a, b, c);
  67
  68       k += 12;
  69       len -= 12;
  70     }
  71
  72   c += length;
  73   switch (len)
  74     {
  75     case 11:
  76       c += ((u_int32_t) k[10] << 24);
  77     case 10:
  78       c += ((u_int32_t) k[9] << 16);
  79     case 9:
  80       c += ((u_int32_t) k[8] << 8);
  81     case 8:
  82       b += ((u_int32_t) k[7] << 24);
  83     case 7:
  84       b += ((u_int32_t) k[6] << 16);
  85     case 6:
  86       b += ((u_int32_t) k[5] << 8);
  87     case 5:
  88       b += k[4];
  89     case 4:
  90       a += ((u_int32_t) k[3] << 24);
  91     case 3:
  92       a += ((u_int32_t) k[2] << 16);
  93     case 2:
  94       a += ((u_int32_t) k[1] << 8);
  95     case 1:
  96       a += k[0];
  97     };
  98
  99   __jhash_mix (a, b, c);
 100
 101   return c;
 102 }
 103
 104 /* A special optimized version that handles 1 or more of u_int32_ts.
 105  * The length parameter here is the number of u_int32_ts in the key.
 106  */
 107 u_int32_t
 108 jhash2 (u_int32_t * k, u_int32_t length, u_int32_t initval)
 109 {
 110   u_int32_t a, b, c, len;
 111
 112   a = b = JHASH_GOLDEN_RATIO;
 113   c = initval;
 114   len = length;
 115
 116   while (len >= 3)
 117     {
 118       a += k[0];
 119       b += k[1];
 120       c += k[2];
 121       __jhash_mix (a, b, c);
 122       k += 3;
 123       len -= 3;
 124     }
 125
 126   c += length * 4;
 127
 128   switch (len)
 129     {
 130     case 2:
 131       b += k[1];
 132     case 1:
 133       a += k[0];
 134     };
 135
 136   __jhash_mix (a, b, c);
 137
 138   return c;
 139 }
 140
 141
 142 /* A special ultra-optimized versions that knows they are hashing exactly
 143  * 3, 2 or 1 word(s).
 144  *
 145  * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
 146  *       done at the end is not done here.
 147  */
 148 u_int32_t
 149 jhash_3words (u_int32_t a, u_int32_t b, u_int32_t c, u_int32_t initval)
 150 {
 151   a += JHASH_GOLDEN_RATIO;
 152   b += JHASH_GOLDEN_RATIO;
 153   c += initval;
 154
 155   __jhash_mix (a, b, c);
 156
 157   return c;
 158 }
 159
 160 u_int32_t
 161 jhash_2words (u_int32_t a, u_int32_t b, u_int32_t initval)
 162 {
 163   return jhash_3words (a, b, 0, initval);
 164 }
 165
 166 u_int32_t
 167 jhash_1word (u_int32_t a, u_int32_t initval)
 168 {
 169   return jhash_3words (a, 0, 0, initval);
 170 }