jhash.h

xenomai 很好的linux实时补丁

/*
 * Jenkins hash support, lifted from the Linux kernel from
 * linux/include/linux/jhash.h.  We use it to index Xenomai shadow
 * TCBs on pthread descriptor addresses.
 *
 * Original credits:
 *
 * Copyright (C) 1996 Bob Jenkins ([e-mail])
 *
 * 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 ([e-mail])
 *
 * I've modified Bob's hash to be useful in the Linux kernel, and
 * any bugs present are surely my fault.  -DaveM
 */

#ifndef _XENO_POSIX_JHASH_H
#define _XENO_POSIX_JHASH_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 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;
}

#endif /* _XENO_POSIX_JHASH_H */