usr/src/lib/libc/db/hash/hfunc.c

/*-
 * Copyright (c) 1990 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[] = "@(#)hfunc.c     5.1 (Berkeley) 2/12/91";
#endif /* LIBC_SCCS and not lint */

/* Global default hash function */
static  int     hash1();
static  int     hash2();
static  int     hash3();
static  int     hash4();

int     (*default_hash)() = 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

static int
hash1(key,len)
char *key;
int len;
{
        register int h;
        register int l = len;
        register unsigned char *k = (unsigned char *) key;

        h = 0;
        /*
         * Convert string to integer
         */
        while (l--) h = h * PRIME1 ^ (*k++ - ' ');
        h %= PRIME2;

        return (h);
}

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

static int
hash2(str, n)
        register unsigned char *str;
        int n;
{
        register unsigned char *e, c;
        register int h;

        e = str + n;
        for (h = 0; str != e;) {
                c = *str++;
                if (!c && str > 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 int
hash3(key,nbytes)
char *key;
int nbytes;
{
        register int n = 0;
        register char *str = key;
        register int loop;
        register int len = nbytes;

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

        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);
}

/* Hash function from Chris Torek */
static int
hash4(key,nbytes)
char    *key;
int     nbytes;
{
        register int h = 0;
        register char *p = key;
        register int loop;
        register int len = nbytes;

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

        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);
}