LXR linux/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 */
  70static 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 */
 117static 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) */
 149static 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
 160static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
 161{
 162        return jhash_3words(a, b, 0, initval);
 163}
 164
 165static inline u32 jhash_1word(u32 a, u32 initval)
 166{
 167        return jhash_3words(a, 0, 0, initval);
 168}
 169
 170#endif /* _LINUX_JHASH_H */
 171