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 (const void *key, u_int32_t length, u_int32_t initval)
  46 {
  47   u_int32_t a, b, c, len;
  48   const 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       /* fallthru */
  78     case 10:
  79       c += ((u_int32_t) k[9] << 16);
  80       /* fallthru */
  81     case 9:
  82       c += ((u_int32_t) k[8] << 8);
  83       /* fallthru */
  84     case 8:
  85       b += ((u_int32_t) k[7] << 24);
  86       /* fallthru */
  87     case 7:
  88       b += ((u_int32_t) k[6] << 16);
  89       /* fallthru */
  90     case 6:
  91       b += ((u_int32_t) k[5] << 8);
  92       /* fallthru */
  93     case 5:
  94       b += k[4];
  95       /* fallthru */
  96     case 4:
  97       a += ((u_int32_t) k[3] << 24);
  98       /* fallthru */
  99     case 3:
 100       a += ((u_int32_t) k[2] << 16);
 101       /* fallthru */
 102     case 2:
 103       a += ((u_int32_t) k[1] << 8);
 104       /* fallthru */
 105     case 1:
 106       a += k[0];
 107     };
 108
 109   __jhash_mix (a, b, c);
 110
 111   return c;
 112 }
 113
 114 /* A special optimized version that handles 1 or more of u_int32_ts.
 115  * The length parameter here is the number of u_int32_ts in the key.
 116  */
 117 u_int32_t
 118 jhash2 (const u_int32_t *k, u_int32_t length, u_int32_t initval)
 119 {
 120   u_int32_t a, b, c, len;
 121
 122   a = b = JHASH_GOLDEN_RATIO;
 123   c = initval;
 124   len = length;
 125
 126   while (len >= 3)
 127     {
 128       a += k[0];
 129       b += k[1];
 130       c += k[2];
 131       __jhash_mix (a, b, c);
 132       k += 3;
 133       len -= 3;
 134     }
 135
 136   c += length * 4;
 137
 138   switch (len)
 139     {
 140     case 2:
 141       b += k[1];
 142       /* fallthru */
 143     case 1:
 144       a += k[0];
 145     };
 146
 147   __jhash_mix (a, b, c);
 148
 149   return c;
 150 }
 151
 152
 153 /* A special ultra-optimized versions that knows they are hashing exactly
 154  * 3, 2 or 1 word(s).
 155  *
 156  * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
 157  *       done at the end is not done here.
 158  */
 159 u_int32_t
 160 jhash_3words (u_int32_t a, u_int32_t b, u_int32_t c, u_int32_t initval)
 161 {
 162   a += JHASH_GOLDEN_RATIO;
 163   b += JHASH_GOLDEN_RATIO;
 164   c += initval;
 165
 166   __jhash_mix (a, b, c);
 167
 168   return c;
 169 }
 170
 171 u_int32_t
 172 jhash_2words (u_int32_t a, u_int32_t b, u_int32_t initval)
 173 {
 174   return jhash_3words (a, b, 0, initval);
 175 }
 176
 177 u_int32_t
 178 jhash_1word (u_int32_t a, u_int32_t initval)
 179 {
 180   return jhash_3words (a, 0, 0, initval);
 181 }