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         switch (length) {
  89         case 12: c += (u32)k[11]<<24;   /* fall through */
  90         case 11: c += (u32)k[10]<<16;   /* fall through */
  91         case 10: c += (u32)k[9]<<8;     /* fall through */
  92         case 9:  c += k[8];             /* fall through */
  93         case 8:  b += (u32)k[7]<<24;    /* fall through */
  94         case 7:  b += (u32)k[6]<<16;    /* fall through */
  95         case 6:  b += (u32)k[5]<<8;     /* fall through */
  96         case 5:  b += k[4];             /* fall through */
  97         case 4:  a += (u32)k[3]<<24;    /* fall through */
  98         case 3:  a += (u32)k[2]<<16;    /* fall through */
  99         case 2:  a += (u32)k[1]<<8;     /* fall through */
 100         case 1:  a += k[0];
 101                  __jhash_final(a, b, c);
 102         case 0: /* Nothing left to add */
 103                 break;
 104         }
 105
 106         return c;
 107 }
 108
 109 /* jhash2 - hash an array of u32's
 110  * @k: the key which must be an array of u32's
 111  * @length: the number of u32's in the key
 112  * @initval: the previous hash, or an arbitray value
 113  *
 114  * Returns the hash value of the key.
 115  */
 116 static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
 117 {
 118         u32 a, b, c;
 119
 120         /* Set up the internal state */
 121         a = b = c = JHASH_INITVAL + (length<<2) + initval;
 122
 123         /* Handle most of the key */
 124         while (length > 3) {
 125                 a += k[0];
 126                 b += k[1];
 127                 c += k[2];
 128                 __jhash_mix(a, b, c);
 129                 length -= 3;
 130                 k += 3;
 131         }
 132
 133         /* Handle the last 3 u32's */
 134         switch (length) {
 135         case 3: c += k[2];      /* fall through */
 136         case 2: b += k[1];      /* fall through */
 137         case 1: a += k[0];
 138                 __jhash_final(a, b, c);
 139         case 0: /* Nothing left to add */
 140                 break;
 141         }
 142
 143         return c;
 144 }
 145
 146
 147 /* __jhash_nwords - hash exactly 3, 2 or 1 word(s) */
 148 static inline u32 __jhash_nwords(u32 a, u32 b, u32 c, u32 initval)
 149 {
 150         a += initval;
 151         b += initval;
 152         c += initval;
 153
 154         __jhash_final(a, b, c);
 155
 156         return c;
 157 }
 158
 159 static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
 160 {
 161         return __jhash_nwords(a, b, c, initval + JHASH_INITVAL + (3 << 2));
 162 }
 163
 164 static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
 165 {
 166         return __jhash_nwords(a, b, 0, initval + JHASH_INITVAL + (2 << 2));
 167 }
 168
 169 static inline u32 jhash_1word(u32 a, u32 initval)
 170 {
 171         return __jhash_nwords(a, 0, 0, initval + JHASH_INITVAL + (1 << 2));
 172 }
 173
 174 #endif /* _LINUX_JHASH_H */