libdb2/hash/hash_func.c

/*-
 * 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);
}