myvtm/libtoolkit/jhash.h

#ifndef _LINUX_JHASH_H
#define _LINUX_JHASH_H

#include "stdint.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 uint32_t jhash(const void *key, uint32_t length, uint32_t initval)
{
	uint32_t a, b, c, len;
	const uint8_t *k = (const uint8_t *)key;

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

	while (len >= 12) {
		a += (k[0] +((uint32_t)k[1]<<8) +((uint32_t)k[2]<<16) +((uint32_t)k[3]<<24));
		b += (k[4] +((uint32_t)k[5]<<8) +((uint32_t)k[6]<<16) +((uint32_t)k[7]<<24));
		c += (k[8] +((uint32_t)k[9]<<8) +((uint32_t)k[10]<<16)+((uint32_t)k[11]<<24));

		__jhash_mix(a,b,c);

		k += 12;
		len -= 12;
	}

	c += length;
	switch (len) {
	case 11: 
		c += ((uint32_t)k[10]<<24);
		break;
	case 10: 
		c += ((uint32_t)k[9]<<16);
		break;
	case 9 : 
		c += ((uint32_t)k[8]<<8);
		break;
	case 8 : 
		b += ((uint32_t)k[7]<<24);
		break;
	case 7 : 
		b += ((uint32_t)k[6]<<16);
		break;
	case 6 : 
		b += ((uint32_t)k[5]<<8);
		break;
	case 5 : 
		b += k[4];
		break;
	case 4 : 
		a += ((uint32_t)k[3]<<24);
		break;
	case 3 : 
		a += ((uint32_t)k[2]<<16);
		break;
	case 2 : 
		a += ((uint32_t)k[1]<<8);
		break;
	case 1 : 
		a += k[0];
		break;
	default:
		break;
	};

	__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 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];
		break;
	case 1 : 
		a += k[0];
		break;
	default:
		break;
	};

	__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 uint32_t jhash_3words(uint32_t a, uint32_t b, uint32_t c, uint32_t initval)
{
	a += JHASH_GOLDEN_RATIO;
	b += JHASH_GOLDEN_RATIO;
	c += initval;

	__jhash_mix(a, b, c);

	return c;
}

static __inline uint32_t jhash_2words(uint32_t a, uint32_t b, uint32_t initval)
{
	return jhash_3words(a, b, 0, initval);
}

static __inline uint32_t jhash_1word(uint32_t a, uint32_t initval)
{
	return jhash_3words(a, 0, 0, initval);
}

#endif /* _LINUX_JHASH_H */