/*-

 * Copyright (c) 1990, 1993

 *	The Regents of the University of California.  All rights reserved.

 *

 * This code is derived from software contributed to Berkeley by

 * Margo Seltzer.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 * 3. All advertising materials mentioning features or use of this software

 *    must display the following acknowledgement:

 *	This product includes software developed by the University of

 *	California, Berkeley and its contributors.

 * 4. Neither the name of the University nor the names of its contributors

 *    may be used to endorse or promote products derived from this software

 *    without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE

 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

 * SUCH DAMAGE.

 */

#if defined(LIBC_SCCS) && !defined(lint)

static char sccsid[] = "@(#)hash_func.c	8.4 (Berkeley) 11/7/95";

#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include "db-int.h"

#include "hash.h"

#include "page.h"

#include "extern.h"

#if 0

static u_int32_t hash1 __P((const void *, size_t));

static u_int32_t hash2 __P((const void *, size_t));

static u_int32_t hash3 __P((const void *, size_t));

#endif

static u_int32_t hash4 __P((const void *, size_t));

/* Default hash function. */

u_int32_t (*__default_hash) __P((const void *, size_t)) = hash4;

/*

 * Assume that we've already split the bucket to which this key hashes,

 * calculate that bucket, and check that in fact we did already split it.

 *

 * EJB's original hsearch hash.

 */

#define PRIME1		37

#define PRIME2		1048583

#if 0

static u_int32_t

hash1(key, len)

	const void *key;

	size_t len;

{

	u_int32_t h;

	u_int8_t *k;

	h = 0;

	k = (u_int8_t *)key;

	/* Convert string to integer */

	while (len--)

		h = h * PRIME1 ^ (*k++ - ' ');

	h %= PRIME2;

	return (h);

}

/*

 * Phong Vo's linear congruential hash

 */

#define dcharhash(h, c)	((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))

static u_int32_t

hash2(key, len)

	const void *key;

	size_t len;

{

	u_int32_t h;

	u_int8_t *e, c, *k;

	k = (u_int8_t *)key;

	e = k + len;

	for (h = 0; k != e;) {

		c = *k++;

		if (!c && k > e)

			break;

		dcharhash(h, c);

	}

	return (h);

}

/*

 * This is INCREDIBLY ugly, but fast.  We break the string up into 8 byte

 * units.  On the first time through the loop we get the "leftover bytes"

 * (strlen % 8).  On every other iteration, we perform 8 HASHC's so we handle

 * all 8 bytes.  Essentially, this saves us 7 cmp & branch instructions.  If

 * this routine is heavily used enough, it's worth the ugly coding.

 *

 * Ozan Yigit's original sdbm hash.

 */

static u_int32_t

hash3(key, len)

	const void *key;

	size_t len;

{

	u_int32_t n, loop;

	u_int8_t *k;

#define HASHC   n = *k++ + 65599 * n

	n = 0;

	k = (u_int8_t *)key;

	if (len > 0) {

		loop = (len + 8 - 1) >> 3;

		switch (len & (8 - 1)) {

		case 0:

			do {	/* All fall throughs */

				HASHC;

		case 7:

				HASHC;

		case 6:

				HASHC;

		case 5:

				HASHC;

		case 4:

				HASHC;

		case 3:

				HASHC;

		case 2:

				HASHC;

		case 1:

				HASHC;

			} while (--loop);

		}

	}

	return (n);

}

#endif

/* Chris Torek's hash function. */

static u_int32_t

hash4(key, len)

	const void *key;

	size_t len;

{

	u_int32_t h, loop;

	const u_int8_t *k;

#define HASH4a   h = (h << 5) - h + *k++;

#define HASH4b   h = (h << 5) + h + *k++;

#define HASH4 HASH4b

	h = 0;

	k = (const u_int8_t *)key;

	if (len > 0) {

		loop = (len + 8 - 1) >> 3;

		switch (len & (8 - 1)) {

		case 0:

			do {	/* All fall throughs */

				HASH4;

		case 7:

				HASH4;

		case 6:

				HASH4;

		case 5:

				HASH4;

		case 4:

				HASH4;

		case 3:

				HASH4;

		case 2:

				HASH4;

		case 1:

				HASH4;

			} while (--loop);

		}

	}

	return (h);

}