h_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. ***REMOVED*** - see
 *    ftp://ftp.cs.berkeley.edu/pub/4bsd/README.Impt.License.Change
 * 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 8.2 (Berkeley) 2/21/94";
#endif /* LIBC_SCCS and not lint */

#ifndef macintosh
#include <sys/types.h>
#endif
#include "mcom_db.h"
#include "hash.h"
#include "page.h"
/* #include "extern.h" */

#if 0
static uint32 hash1(const void *, size_t);
static uint32 hash2(const void *, size_t);
static uint32 hash3(const void *, size_t);
#endif
static uint32 hash4(const void *, size_t);

/* Global default hash function */
uint32 (*dbm_default_hash)(const void *, size_t) = hash4;

/*
 * HASH FUNCTIONS
 *
 * 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.
 *
 * This came from ejb's hsearch.
 */

#define PRIME1 37
#define PRIME2 1048583

#if 0
static uint32
hash1(const void *keyarg, register size_t len)
{
    register const uint8 *key;
    register uint32 h;

    /* Convert string to integer */
    for (key = (const uint8 *)keyarg, h = 0; len--;)
        h = h * PRIME1 ^ (*key++ - ' ');
    h %= PRIME2;
    return (h);
}

/*
 * Phong's linear congruential hash
 */
#define dcharhash(h, c) ((h) = 0x63c63cd9 * (h) + 0x9c39c33d + (c))

static uint32
hash2(const void *keyarg, size_t len)
{
    register const uint8 *e, *key;
    register uint32 h;
    register uint8 c;

    key = (const uint8 *)keyarg;
    e = key + len;
    for (h = 0; key != e;) {
        c = *key++;
        if (!c && key > 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.
 *
 * OZ's original sdbm hash
 */
static uint32
hash3(const void *keyarg, register size_t len)
{
    register const uint8 *key;
    register size_t loop;
    register uint32 h;

#define HASHC h = *key++ + 65599 * h

    h = 0;
    key = (const uint8 *)keyarg;
    if (len > 0) {
        loop = (len + 8 - 1) >> 3;

        switch (len & (8 - 1)) {
        case 0:
            do {
                HASHC;
                /* FALLTHROUGH */
        case 7:
                HASHC;
                /* FALLTHROUGH */
        case 6:
                HASHC;
                /* FALLTHROUGH */
        case 5:
                HASHC;
                /* FALLTHROUGH */
        case 4:
                HASHC;
                /* FALLTHROUGH */
        case 3:
                HASHC;
                /* FALLTHROUGH */
        case 2:
                HASHC;
                /* FALLTHROUGH */
        case 1:
                HASHC;
            } while (--loop);
        }
    }
    return (h);
}
#endif /* 0 */

/* Hash function from Chris Torek. */
static uint32
hash4(const void *keyarg, register size_t len)
{
    register const uint8 *key;
    register size_t loop;
    register uint32 h;

#define HASH4a h = (h << 5) - h + *key++;
#define HASH4b h = (h << 5) + h + *key++;
#define HASH4 HASH4b

    h = 0;
    key = (const uint8 *)keyarg;
    if (len > 0) {
        loop = (len + 8 - 1) >> 3;

        switch (len & (8 - 1)) {
            case 0:
                do {
                    HASH4;
                    /* FALLTHROUGH */
                    case 7:
                        HASH4;
                    /* FALLTHROUGH */
                    case 6:
                        HASH4;
                    /* FALLTHROUGH */
                    case 5:
                        HASH4;
                    /* FALLTHROUGH */
                    case 4:
                        HASH4;
                    /* FALLTHROUGH */
                    case 3:
                        HASH4;
                    /* FALLTHROUGH */
                    case 2:
                        HASH4;
                    /* FALLTHROUGH */
                    case 1:
                        HASH4;
                } while (--loop);
        }
    }
    return (h);
}