include/nucleus/jhash.h

/*
 * Jenkins hash support, lifted from the Linux kernel from
 * linux/include/linux/jhash.h.
 *
 * Original credits:
 *
 * Copyright (C) 1996 Bob Jenkins ([email protected])
 *
 * 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 ([email protected])
 *
 * I've modified Bob's hash to be useful in the Linux kernel, and
 * any bugs present are surely my fault.  -DaveM
 */

#ifndef _XENO_NUCLEUS_JHASH_H
#define _XENO_NUCLEUS_JHASH_H

#include <nucleus/types.h>

/* 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 ratio: an arbitrary value */
#define JHASH_GOLDEN_RATIO      0x9e3779b9

/* 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 uint32_t jhash2(const uint32_t *k, uint32_t length, uint32_t initval)
{
        uint32_t 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;
}

#endif /* _XENO_NUCLEUS_JHASH_H */