mirror_frr/lib/jhash.c

/* 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
 */

#include "zebra.h"
#include "jhash.h"

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

/* 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 most generic version, hashes an arbitrary sequence
 * of bytes.  No alignment or length assumptions are made about
 * the input key.
 */
uint32_t jhash(const void *key, uint32_t length, uint32_t initval)
{
	uint32_t a, b, c, len;
	const uint8_t *k = 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);
	/* fallthru */
	case 10:
		c += ((uint32_t)k[9] << 16);
	/* fallthru */
	case 9:
		c += ((uint32_t)k[8] << 8);
	/* fallthru */
	case 8:
		b += ((uint32_t)k[7] << 24);
	/* fallthru */
	case 7:
		b += ((uint32_t)k[6] << 16);
	/* fallthru */
	case 6:
		b += ((uint32_t)k[5] << 8);
	/* fallthru */
	case 5:
		b += k[4];
	/* fallthru */
	case 4:
		a += ((uint32_t)k[3] << 24);
	/* fallthru */
	case 3:
		a += ((uint32_t)k[2] << 16);
	/* fallthru */
	case 2:
		a += ((uint32_t)k[1] << 8);
	/* fallthru */
	case 1:
		a += k[0];
	}

	__jhash_mix(a, b, c);

	return c;
}

/* A special optimized version that handles 1 or more of uint32_ts.
 * The length parameter here is the number of uint32_ts in the key.
 */
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];
	/* fallthru */
	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.
 */
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;
}

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

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