urcu/jhash.h

   1 #ifndef _KCOMPAT_JHASH_H
   2 #define _KCOMPAT_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 <stdint.h>
  24
  25 typedef uint8_t u8;
  26 typedef uint32_t u32;
  27
  28 /* NOTE: Arguments are modified. */
  29 #define __jhash_mix(a, b, c) \
  30 { \
  31   a -= b; a -= c; a ^= (c>>13); \
  32   b -= c; b -= a; b ^= (a<<8); \
  33   c -= a; c -= b; c ^= (b>>13); \
  34   a -= b; a -= c; a ^= (c>>12);  \
  35   b -= c; b -= a; b ^= (a<<16); \
  36   c -= a; c -= b; c ^= (b>>5); \
  37   a -= b; a -= c; a ^= (c>>3);  \
  38   b -= c; b -= a; b ^= (a<<10); \
  39   c -= a; c -= b; c ^= (b>>15); \
  40 }
  41
  42 /* The golden ration: an arbitrary value */
  43 #define JHASH_GOLDEN_RATIO      0x9e3779b9
  44
  45 /* The most generic version, hashes an arbitrary sequence
  46  * of bytes.  No alignment or length assumptions are made about
  47  * the input key.
  48  */
  49 static inline u32 jhash(const void *key, u32 length, u32 initval)
  50 {
  51         u32 a, b, c, len;
  52         const u8 *k = key;
  53
  54         len = length;
  55         a = b = JHASH_GOLDEN_RATIO;
  56         c = initval;
  57
  58         while (len >= 12) {
  59                 a += (k[0] +((u32)k[1]<<8) +((u32)k[2]<<16) +((u32)k[3]<<24));
  60                 b += (k[4] +((u32)k[5]<<8) +((u32)k[6]<<16) +((u32)k[7]<<24));
  61                 c += (k[8] +((u32)k[9]<<8) +((u32)k[10]<<16)+((u32)k[11]<<24));
  62
  63                 __jhash_mix(a,b,c);
  64
  65                 k += 12;
  66                 len -= 12;
  67         }
  68
  69         c += length;
  70         switch (len) {
  71         case 11: c += ((u32)k[10]<<24);
  72         case 10: c += ((u32)k[9]<<16);
  73         case 9 : c += ((u32)k[8]<<8);
  74         case 8 : b += ((u32)k[7]<<24);
  75         case 7 : b += ((u32)k[6]<<16);
  76         case 6 : b += ((u32)k[5]<<8);
  77         case 5 : b += k[4];
  78         case 4 : a += ((u32)k[3]<<24);
  79         case 3 : a += ((u32)k[2]<<16);
  80         case 2 : a += ((u32)k[1]<<8);
  81         case 1 : a += k[0];
  82         };
  83
  84         __jhash_mix(a,b,c);
  85
  86         return c;
  87 }
  88
  89 #endif /* _KCOMPAT_JHASH_H */