root/include/linux/jhash.h

INCLUDED FROM

DEFINITIONS

1. jhash
2. jhash2
3. jhash_3words
4. jhash_2words
5. jhash_1word

#ifndef _LINUX_JHASH_H
#define _LINUX_JHASH_H

/* jhash.h: Jenkins hash support.
 *
 * Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net)
 *
 * http://burtleburtle.net/bob/hash/
 *
 * These are the credits from Bob's sources:
 *
 * lookup2.c, by Bob Jenkins, December 1996, Public Domain.
 * hash(), hash2(), hash3, and mix() are externally useful functions.
 * Routines to test the hash are included if SELF_TEST is defined.
 * You can use this free for any purpose.  It has no warranty.
 *
 * Copyright (C) 2003 David S. Miller (davem@redhat.com)
 *
 * I've modified Bob's hash to be useful in the Linux kernel, and
 * any bugs present are surely my fault.  -DaveM
 */

/* NOTE: Arguments are modified. */
#define __jhash_mix(a, b, c) \
{ \
  a -= b; a -= c; a ^= (c>>13); \
  b -= c; b -= a; b ^= (a<<8); \
  c -= a; c -= b; c ^= (b>>13); \
  a -= b; a -= c; a ^= (c>>12);  \
  b -= c; b -= a; b ^= (a<<16); \
  c -= a; c -= b; c ^= (b>>5); \
  a -= b; a -= c; a ^= (c>>3);  \
  b -= c; b -= a; b ^= (a<<10); \
  c -= a; c -= b; c ^= (b>>15); \
}

/* The golden ration: an arbitrary value */
#define JHASH_GOLDEN_RATIO      0x9e3779b9

/* The most generic version, hashes an arbitrary sequence
 * of bytes.  No alignment or length assumptions are made about
 * the input key.
 */
static inline u32 jhash(const void *key, u32 length, u32 initval)
{
        u32 a, b, c, len;
        const u8 *k = key;

        len = length;
        a = b = JHASH_GOLDEN_RATIO;
        c = initval;

        while (len >= 12) {
                a += (k[0] +((u32)k[1]<<8) +((u32)k[2]<<16) +((u32)k[3]<<24));
                b += (k[4] +((u32)k[5]<<8) +((u32)k[6]<<16) +((u32)k[7]<<24));
                c += (k[8] +((u32)k[9]<<8) +((u32)k[10]<<16)+((u32)k[11]<<24));

                __jhash_mix(a,b,c);

                k += 12;
                len -= 12;
        }

        c += length;
        switch (len) {
        case 11: c += ((u32)k[10]<<24);
        case 10: c += ((u32)k[9]<<16);
        case 9 : c += ((u32)k[8]<<8);
        case 8 : b += ((u32)k[7]<<24);
        case 7 : b += ((u32)k[6]<<16);
        case 6 : b += ((u32)k[5]<<8);
        case 5 : b += k[4];
        case 4 : a += ((u32)k[3]<<24);
        case 3 : a += ((u32)k[2]<<16);
        case 2 : a += ((u32)k[1]<<8);
        case 1 : a += k[0];
        };

        __jhash_mix(a,b,c);

        return c;
}

/* A special optimized version that handles 1 or more of u32s.
 * The length parameter here is the number of u32s in the key.
 */
static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
{
        u32 a, b, c, len;

        a = b = JHASH_GOLDEN_RATIO;
        c = initval;
        len = length;

        while (len >= 3) {
                a += k[0];
                b += k[1];
                c += k[2];
                __jhash_mix(a, b, c);
                k += 3; len -= 3;
        }

        c += length * 4;

        switch (len) {
        case 2 : b += k[1];
        case 1 : a += k[0];
        };

        __jhash_mix(a,b,c);

        return c;
}


/* A special ultra-optimized versions that knows they are hashing exactly
 * 3, 2 or 1 word(s).
 *
 * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
 *       done at the end is not done here.
 */
static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
{
        a += JHASH_GOLDEN_RATIO;
        b += JHASH_GOLDEN_RATIO;
        c += initval;

        __jhash_mix(a, b, c);

        return c;
}

static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
{
        return jhash_3words(a, b, 0, initval);
}

static inline u32 jhash_1word(u32 a, u32 initval)
{
        return jhash_3words(a, 0, 0, initval);
}

#endif /* _LINUX_JHASH_H */