include/linux/jhash.h

   1 #ifndef _LINUX_JHASH_H
   2 #define _LINUX_JHASH_H
   3
   4 /* jhash.h: Jenkins hash support.
   5  *
   6  * Copyright (C) 2006. 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  * lookup3.c, by Bob Jenkins, May 2006, Public Domain.
  13  *
  14  * These are functions for producing 32-bit hashes for hash table lookup.
  15  * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
  16  * are externally useful functions.  Routines to test the hash are included
  17  * if SELF_TEST is defined.  You can use this free for any purpose.  It's in
  18  * the public domain.  It has no warranty.
  19  *
  20  * Copyright (C) 2009-2010 Jozsef Kadlecsik (kadlec@blackhole.kfki.hu)
  21  *
  22  * I've modified Bob's hash to be useful in the Linux kernel, and
  23  * any bugs present are my fault.
  24  * Jozsef
  25  */
  26 #include <linux/bitops.h>
  27 #include <linux/unaligned/packed_struct.h>
  28
  29 /* Best hash sizes are of power of two */
  30 #define jhash_size(n)   ((u32)1<<(n))
  31 /* Mask the hash value, i.e (value & jhash_mask(n)) instead of (value % n) */
  32 #define jhash_mask(n)   (jhash_size(n)-1)
  33
  34 /* __jhash_mix -- mix 3 32-bit values reversibly. */
  35 #define __jhash_mix(a, b, c)                    \
  36 {                                               \
  37         a -= c;  a ^= rol32(c, 4);  c += b;     \
  38         b -= a;  b ^= rol32(a, 6);  a += c;     \
  39         c -= b;  c ^= rol32(b, 8);  b += a;     \
  40         a -= c;  a ^= rol32(c, 16); c += b;     \
  41         b -= a;  b ^= rol32(a, 19); a += c;     \
  42         c -= b;  c ^= rol32(b, 4);  b += a;     \
  43 }
  44
  45 /* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
  46 #define __jhash_final(a, b, c)                  \
  47 {                                               \
  48         c ^= b; c -= rol32(b, 14);              \
  49         a ^= c; a -= rol32(c, 11);              \
  50         b ^= a; b -= rol32(a, 25);              \
  51         c ^= b; c -= rol32(b, 16);              \
  52         a ^= c; a -= rol32(c, 4);               \
  53         b ^= a; b -= rol32(a, 14);              \
  54         c ^= b; c -= rol32(b, 24);              \
  55 }
  56
  57 /* An arbitrary initial parameter */
  58 #define JHASH_INITVAL           0xdeadbeef
  59
  60 /* jhash - hash an arbitrary key
  61  * @k: sequence of bytes as key
  62  * @length: the length of the key
  63  * @initval: the previous hash, or an arbitray value
  64  *
  65  * The generic version, hashes an arbitrary sequence of bytes.
  66  * No alignment or length assumptions are made about the input key.
  67  *
  68  * Returns the hash value of the key. The result depends on endianness.
  69  */
  70 static inline u32 jhash(const void *key, u32 length, u32 initval)
  71 {
  72         u32 a, b, c;
  73         const u8 *k = key;
  74
  75         /* Set up the internal state */
  76         a = b = c = JHASH_INITVAL + length + initval;
  77
  78         /* All but the last block: affect some 32 bits of (a,b,c) */
  79         while (length > 12) {
  80                 a += __get_unaligned_cpu32(k);
  81                 b += __get_unaligned_cpu32(k + 4);
  82                 c += __get_unaligned_cpu32(k + 8);
  83                 __jhash_mix(a, b, c);
  84                 length -= 12;
  85                 k += 12;
  86         }
  87         /* Last block: affect all 32 bits of (c) */
  88         /* All the case statements fall through */
  89         switch (length) {
  90         case 12: c += (u32)k[11]<<24;
  91         case 11: c += (u32)k[10]<<16;
  92         case 10: c += (u32)k[9]<<8;
  93         case 9:  c += k[8];
  94         case 8:  b += (u32)k[7]<<24;
  95         case 7:  b += (u32)k[6]<<16;
  96         case 6:  b += (u32)k[5]<<8;
  97         case 5:  b += k[4];
  98         case 4:  a += (u32)k[3]<<24;
  99         case 3:  a += (u32)k[2]<<16;
 100         case 2:  a += (u32)k[1]<<8;
 101         case 1:  a += k[0];
 102                  __jhash_final(a, b, c);
 103         case 0: /* Nothing left to add */
 104                 break;
 105         }
 106
 107         return c;
 108 }
 109
 110 /* jhash2 - hash an array of u32's
 111  * @k: the key which must be an array of u32's
 112  * @length: the number of u32's in the key
 113  * @initval: the previous hash, or an arbitray value
 114  *
 115  * Returns the hash value of the key.
 116  */
 117 static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
 118 {
 119         u32 a, b, c;
 120
 121         /* Set up the internal state */
 122         a = b = c = JHASH_INITVAL + (length<<2) + initval;
 123
 124         /* Handle most of the key */
 125         while (length > 3) {
 126                 a += k[0];
 127                 b += k[1];
 128                 c += k[2];
 129                 __jhash_mix(a, b, c);
 130                 length -= 3;
 131                 k += 3;
 132         }
 133
 134         /* Handle the last 3 u32's: all the case statements fall through */
 135         switch (length) {
 136         case 3: c += k[2];
 137         case 2: b += k[1];
 138         case 1: a += k[0];
 139                 __jhash_final(a, b, c);
 140         case 0: /* Nothing left to add */
 141                 break;
 142         }
 143
 144         return c;
 145 }
 146
 147
 148 /* jhash_3words - hash exactly 3, 2 or 1 word(s) */
 149 static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
 150 {
 151         a += JHASH_INITVAL;
 152         b += JHASH_INITVAL;
 153         c += initval;
 154
 155         __jhash_final(a, b, c);
 156
 157         return c;
 158 }
 159
 160 static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
 161 {
 162         return jhash_3words(a, b, 0, initval);
 163 }
 164
 165 static inline u32 jhash_1word(u32 a, u32 initval)
 166 {
 167         return jhash_3words(a, 0, 0, initval);
 168 }
 169
 170 #endif /* _LINUX_JHASH_H */