exec/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 typedef uint32_t u32;
  24 typedef uint8_t u8;
  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 golden ration: an arbitrary value */
  41 #define JHASH_GOLDEN_RATIO      0x9e3779b9
  42
  43 /* The most generic version, hashes an arbitrary sequence
  44  * of bytes.  No alignment or length assumptions are made about
  45  * the input key.
  46  */
  47 static inline u32 jhash(const void *key, u32 length, u32 initval)
  48 {
  49         u32 a, b, c, len;
  50         const u8 *k = key;
  51
  52         len = length;
  53         a = b = JHASH_GOLDEN_RATIO;
  54         c = initval;
  55
  56         while (len >= 12) {
  57                 a += (k[0] +((u32)k[1]<<8) +((u32)k[2]<<16) +((u32)k[3]<<24));
  58                 b += (k[4] +((u32)k[5]<<8) +((u32)k[6]<<16) +((u32)k[7]<<24));
  59                 c += (k[8] +((u32)k[9]<<8) +((u32)k[10]<<16)+((u32)k[11]<<24));
  60
  61                 __jhash_mix(a,b,c);
  62
  63                 k += 12;
  64                 len -= 12;
  65         }
  66
  67         c += length;
  68         switch (len) {
  69         case 11: c += ((u32)k[10]<<24);
  70         case 10: c += ((u32)k[9]<<16);
  71         case 9 : c += ((u32)k[8]<<8);
  72         case 8 : b += ((u32)k[7]<<24);
  73         case 7 : b += ((u32)k[6]<<16);
  74         case 6 : b += ((u32)k[5]<<8);
  75         case 5 : b += k[4];
  76         case 4 : a += ((u32)k[3]<<24);
  77         case 3 : a += ((u32)k[2]<<16);
  78         case 2 : a += ((u32)k[1]<<8);
  79         case 1 : a += k[0];
  80         };
  81
  82         __jhash_mix(a,b,c);
  83
  84         return c;
  85 }
  86
  87 /* A special optimized version that handles 1 or more of u32s.
  88  * The length parameter here is the number of u32s in the key.
  89  */
  90 static inline u32 jhash2(u32 *k, u32 length, u32 initval)
  91 {
  92         u32 a, b, c, len;
  93
  94         a = b = JHASH_GOLDEN_RATIO;
  95         c = initval;
  96         len = length;
  97
  98         while (len >= 3) {
  99                 a += k[0];
 100                 b += k[1];
 101                 c += k[2];
 102                 __jhash_mix(a, b, c);
 103                 k += 3; len -= 3;
 104         }
 105
 106         c += length * 4;
 107
 108         switch (len) {
 109         case 2 : b += k[1];
 110         case 1 : a += k[0];
 111         };
 112
 113         __jhash_mix(a,b,c);
 114
 115         return c;
 116 }
 117
 118
 119 /* A special ultra-optimized versions that knows they are hashing exactly
 120  * 3, 2 or 1 word(s).
 121  *
 122  * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
 123  *       done at the end is not done here.
 124  */
 125 static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
 126 {
 127         a += JHASH_GOLDEN_RATIO;
 128         b += JHASH_GOLDEN_RATIO;
 129         c += initval;
 130
 131         __jhash_mix(a, b, c);
 132
 133         return c;
 134 }
 135
 136 static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
 137 {
 138         return jhash_3words(a, b, 0, initval);
 139 }
 140
 141 static inline u32 jhash_1word(u32 a, u32 initval)
 142 {
 143         return jhash_3words(a, 0, 0, initval);
 144 }
 145
 146 #endif /* _LINUX_JHASH_H */