hash_func.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 1996, 1997
* Sleepycat Software. All rights reserved.
*/
/*
* Copyright (c) 1990, 1993
* Margo Seltzer. All rights reserved.
*/
/*
* 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
* 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.
*/
/*
* Copyright (c) 1998 by Sun Microsystems, Inc.
* All rights reserved.
*/
#include "config.h"
#pragma ident "%Z%%M% %I% %E% SMI"
#ifndef lint
static const char sccsid[] = "@(#)hash_func.c 10.7 (Sleepycat) 9/16/97";
static const char sccsi2[] = "%W% (Sun) %G%";
#endif /* not lint */
#ifndef NO_SYSTEM_INCLUDES
#endif
#include "db_int.h"
#include "db_page.h"
#include "hash.h"
/*
* __ham_func2 --
* Phong Vo's linear congruential hash.
*
* PUBLIC: u_int32_t __ham_func2 __P((const void *, u_int32_t));
*/
const void *key;
{
const u_int8_t *e, *k;
u_int32_t h;
u_int8_t c;
k = key;
e = k + len;
for (h = 0; k != e;) {
c = *k++;
if (!c && k > e)
break;
DCHARHASH(h, c);
}
return (h);
}
/*
* __ham_func3 --
* Ozan Yigit's original sdbm hash.
*
* Ugly, but fast. Break the string up into 8 byte units. On the first time
* through the loop get the "leftover bytes" (strlen % 8). On every other
* iteration, perform 8 HASHC's so we handle all 8 bytes. Essentially, this
* saves us 7 cmp & branch instructions.
*
* PUBLIC: u_int32_t __ham_func3 __P((const void *, u_int32_t));
*/
const void *key;
{
const u_int8_t *k;
if (len == 0)
return (0);
#define HASHC n = *k++ + 65599 * n
n = 0;
k = key;
case 0:
do {
case 7:
case 6:
case 5:
case 4:
case 3:
case 2:
case 1:
} while (--loop);
}
return (n);
}
/*
* __ham_func4 --
* Chris Torek's hash function. Although this function performs only
* slightly worse than __ham_func5 on strings, it performs horribly on
* numbers.
*
* PUBLIC: u_int32_t __ham_func4 __P((const void *, u_int32_t));
*/
const void *key;
{
const u_int8_t *k;
if (len == 0)
return (0);
#define HASH4a h = (h << 5) - h + *k++;
#define HASH4b h = (h << 5) + h + *k++;
h = 0;
k = key;
case 0:
do {
case 7:
case 6:
case 5:
case 4:
case 3:
case 2:
case 1:
} while (--loop);
}
return (h);
}
/*
*
* The basis of the hash algorithm was taken from an idea sent by email to the
* IEEE Posix P1003.2 mailing list from Phong Vo (kpv@research.att.com) and
* Glenn Fowler (gsf@research.att.com). Landon Curt Noll (chongo@toad.com)
* later improved on their algorithm.
*
* The magic is in the interesting relationship between the special prime
* 16777619 (2^24 + 403) and 2^32 and 2^8.
*
* This hash produces the fewest collisions of any function that we've seen so
* far, and works well on both numbers and strings.
*
* PUBLIC: u_int32_t __ham_func5 __P((const void *, u_int32_t));
*/
const void *key;
{
const u_int8_t *k, *e;
u_int32_t h;
k = key;
e = k + len;
for (h = 0; k < e; ++k) {
h *= 16777619;
h ^= *k;
}
return (h);
}