BSD 4_4_Lite1 release

[unix-history] / usr / src / contrib / nvi.1.14 / PORT / db.1.73 / 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 8.1 (Berkeley) 6/4/93";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include <db.h>
#include "hash.h"
#include "page.h"
#include "extern.h"

static int hash1 __P((u_char *, int));
static int hash2 __P((u_char *, int));
static int hash3 __P((u_char *, int));
static int hash4 __P((u_char *, int));

/* Global default hash function */
int (*__default_hash) __P((u_char *, int)) = 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)
       register u_char *key;
       register int len;
{
       register int h;

       h = 0;
       /* Convert string to integer */
       while (len--)
               h = h * PRIME1 ^ (*key++ - ' ');
       h %= PRIME2;
       return (h);
}

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

static int
hash2(key, len)
       register u_char *key;
       int len;
{
       register u_char *e, c;
       register int h;

       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 int
hash3(key, len)
       register u_char *key;
       register int len;
{
       register int n, loop;

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

       n = 0;
       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, len)
       register u_char *key;
       register int len;
{
       register int h, loop;

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

       h = 0;
       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);
}