jhash.h

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    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(void *key, u32 length, u32 initval)
   45 {
   46         u32 a, b, c, len;
   47         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(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 */

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FreeBSD/Linux Kernel Cross Reference sys/include/linux/jhash.h

FreeBSD/Linux Kernel Cross Reference
sys/include/linux/jhash.h