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216 lines
5.0 KiB
216 lines
5.0 KiB
/*-
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* See the file LICENSE for redistribution information.
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*
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* Copyright (c) 1996, 1997, 1998, 1999
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* Sleepycat Software. All rights reserved.
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*/
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/*
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* Copyright (c) 1990, 1993
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* Margo Seltzer. All rights reserved.
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*/
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/*
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* Copyright (c) 1990, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* Margo Seltzer.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include "db_config.h"
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#ifndef lint
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static const char sccsid[] = "@(#)hash_func.c 11.2 (Sleepycat) 9/9/99";
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#endif /* not lint */
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#ifndef NO_SYSTEM_INCLUDES
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#include <sys/types.h>
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#endif
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#include "db_int.h"
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#include "db_page.h"
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#include "hash.h"
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/*
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* CDB___ham_func2 --
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* Phong Vo's linear congruential hash.
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*
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* PUBLIC: u_int32_t CDB___ham_func2 __P((const void *, u_int32_t));
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*/
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#define DCHARHASH(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
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u_int32_t
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CDB___ham_func2(key, len)
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const void *key;
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u_int32_t len;
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{
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const u_int8_t *e, *k;
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u_int32_t h;
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u_int8_t c;
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k = key;
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e = k + len;
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for (h = 0; k != e;) {
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c = *k++;
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if (!c && k > e)
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break;
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DCHARHASH(h, c);
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}
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return (h);
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}
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/*
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* CDB___ham_func3 --
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* Ozan Yigit's original sdbm hash.
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*
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* Ugly, but fast. Break the string up into 8 byte units. On the first time
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* through the loop get the "leftover bytes" (strlen % 8). On every other
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* iteration, perform 8 HASHC's so we handle all 8 bytes. Essentially, this
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* saves us 7 cmp & branch instructions.
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*
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* PUBLIC: u_int32_t CDB___ham_func3 __P((const void *, u_int32_t));
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*/
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u_int32_t
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CDB___ham_func3(key, len)
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const void *key;
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u_int32_t len;
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{
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const u_int8_t *k;
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u_int32_t n, loop;
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if (len == 0)
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return (0);
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#define HASHC n = *k++ + 65599 * n
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n = 0;
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k = key;
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loop = (len + 8 - 1) >> 3;
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switch (len & (8 - 1)) {
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case 0:
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do {
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HASHC;
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case 7:
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HASHC;
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case 6:
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HASHC;
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case 5:
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HASHC;
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case 4:
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HASHC;
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case 3:
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HASHC;
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case 2:
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HASHC;
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case 1:
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HASHC;
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} while (--loop);
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}
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return (n);
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}
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/*
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* CDB___ham_func4 --
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* Chris Torek's hash function. Although this function performs only
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* slightly worse than CDB___ham_func5 on strings, it performs horribly on
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* numbers.
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*
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* PUBLIC: u_int32_t CDB___ham_func4 __P((const void *, u_int32_t));
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*/
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u_int32_t
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CDB___ham_func4(key, len)
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const void *key;
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u_int32_t len;
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{
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const u_int8_t *k;
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u_int32_t h, loop;
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if (len == 0)
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return (0);
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#define HASH4a h = (h << 5) - h + *k++;
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#define HASH4b h = (h << 5) + h + *k++;
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#define HASH4 HASH4b
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h = 0;
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k = key;
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loop = (len + 8 - 1) >> 3;
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switch (len & (8 - 1)) {
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case 0:
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do {
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HASH4;
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case 7:
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HASH4;
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case 6:
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HASH4;
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case 5:
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HASH4;
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case 4:
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HASH4;
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case 3:
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HASH4;
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case 2:
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HASH4;
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case 1:
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HASH4;
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} while (--loop);
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}
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return (h);
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}
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/*
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* Fowler/Noll/Vo hash
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*
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* The basis of the hash algorithm was taken from an idea sent by email to the
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* IEEE Posix P1003.2 mailing list from Phong Vo (kpv@research.att.com) and
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* Glenn Fowler (gsf@research.att.com). Landon Curt Noll (chongo@toad.com)
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* later improved on their algorithm.
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*
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* The magic is in the interesting relationship between the special prime
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* 16777619 (2^24 + 403) and 2^32 and 2^8.
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*
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* This hash produces the fewest collisions of any function that we've seen so
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* far, and works well on both numbers and strings.
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*
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* PUBLIC: u_int32_t CDB___ham_func5 __P((const void *, u_int32_t));
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*/
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u_int32_t
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CDB___ham_func5(key, len)
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const void *key;
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u_int32_t len;
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{
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const u_int8_t *k, *e;
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u_int32_t h;
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k = key;
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e = k + len;
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for (h = 0; k < e; ++k) {
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h *= 16777619;
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h ^= *k;
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}
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return (h);
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}
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