1/*-
2 * See the file LICENSE for redistribution information.
3 *
4 * Copyright (c) 1996, 1997
5 *	Sleepycat Software.  All rights reserved.
6 */
7/*
8 * Copyright (c) 1990, 1993
9 *	Margo Seltzer.  All rights reserved.
10 */
11/*
12 * Copyright (c) 1990, 1993
13 *	The Regents of the University of California.  All rights reserved.
14 *
15 * This code is derived from software contributed to Berkeley by
16 * Margo Seltzer.
17 *
18 * Redistribution and use in source and binary forms, with or without
19 * modification, are permitted provided that the following conditions
20 * are met:
21 * 1. Redistributions of source code must retain the above copyright
22 *    notice, this list of conditions and the following disclaimer.
23 * 2. Redistributions in binary form must reproduce the above copyright
24 *    notice, this list of conditions and the following disclaimer in the
25 *    documentation and/or other materials provided with the distribution.
26 * 3. All advertising materials mentioning features or use of this software
27 *    must display the following acknowledgement:
28 *	This product includes software developed by the University of
29 *	California, Berkeley and its contributors.
30 * 4. Neither the name of the University nor the names of its contributors
31 *    may be used to endorse or promote products derived from this software
32 *    without specific prior written permission.
33 *
34 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
35 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
36 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
37 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
38 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
39 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
40 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
41 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
42 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
43 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
44 * SUCH DAMAGE.
45 */
46/*
47 * Copyright (c) 1998 by Sun Microsystems, Inc.
48 * All rights reserved.
49 */
50
51#include "config.h"
52
53#pragma ident	"%Z%%M%	%I%	%E% SMI"
54
55#ifndef lint
56static const char sccsid[] = "@(#)hash_func.c	10.7 (Sleepycat) 9/16/97";
57static const char sccsi2[] = "%W% (Sun) %G%";
58#endif /* not lint */
59
60#ifndef NO_SYSTEM_INCLUDES
61#include <sys/types.h>
62#endif
63
64#include "db_int.h"
65#include "db_page.h"
66#include "hash.h"
67
68/*
69 * __ham_func2 --
70 *	Phong Vo's linear congruential hash.
71 *
72 * PUBLIC: u_int32_t __ham_func2 __P((const void *, u_int32_t));
73 */
74#define	DCHARHASH(h, c)	((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
75
76u_int32_t
77__ham_func2(key, len)
78	const void *key;
79	u_int32_t len;
80{
81	const u_int8_t *e, *k;
82	u_int32_t h;
83	u_int8_t c;
84
85	k = key;
86	e = k + len;
87	for (h = 0; k != e;) {
88		c = *k++;
89		if (!c && k > e)
90			break;
91		DCHARHASH(h, c);
92	}
93	return (h);
94}
95
96/*
97 * __ham_func3 --
98 *	Ozan Yigit's original sdbm hash.
99 *
100 * Ugly, but fast.  Break the string up into 8 byte units.  On the first time
101 * through the loop get the "leftover bytes" (strlen % 8).  On every other
102 * iteration, perform 8 HASHC's so we handle all 8 bytes.  Essentially, this
103 * saves us 7 cmp & branch instructions.
104 *
105 * PUBLIC: u_int32_t __ham_func3 __P((const void *, u_int32_t));
106 */
107u_int32_t
108__ham_func3(key, len)
109	const void *key;
110	u_int32_t len;
111{
112	const u_int8_t *k;
113	u_int32_t n, loop;
114
115	if (len == 0)
116		return (0);
117
118#define	HASHC	n = *k++ + 65599 * n
119	n = 0;
120	k = key;
121
122	loop = (len + 8 - 1) >> 3;
123	switch (len & (8 - 1)) {
124	case 0:
125		do {
126			HASHC;
127	case 7:
128			HASHC;
129	case 6:
130			HASHC;
131	case 5:
132			HASHC;
133	case 4:
134			HASHC;
135	case 3:
136			HASHC;
137	case 2:
138			HASHC;
139	case 1:
140			HASHC;
141		} while (--loop);
142	}
143	return (n);
144}
145
146/*
147 * __ham_func4 --
148 *	Chris Torek's hash function.  Although this function performs only
149 *	slightly worse than __ham_func5 on strings, it performs horribly on
150 *	numbers.
151 *
152 * PUBLIC: u_int32_t __ham_func4 __P((const void *, u_int32_t));
153 */
154u_int32_t
155__ham_func4(key, len)
156	const void *key;
157	u_int32_t len;
158{
159	const u_int8_t *k;
160	u_int32_t h, loop;
161
162	if (len == 0)
163		return (0);
164
165#define	HASH4a	h = (h << 5) - h + *k++;
166#define	HASH4b	h = (h << 5) + h + *k++;
167#define	HASH4	HASH4b
168	h = 0;
169	k = key;
170
171	loop = (len + 8 - 1) >> 3;
172	switch (len & (8 - 1)) {
173	case 0:
174		do {
175			HASH4;
176	case 7:
177			HASH4;
178	case 6:
179			HASH4;
180	case 5:
181			HASH4;
182	case 4:
183			HASH4;
184	case 3:
185			HASH4;
186	case 2:
187			HASH4;
188	case 1:
189			HASH4;
190		} while (--loop);
191	}
192	return (h);
193}
194
195/*
196 * Fowler/Noll/Vo hash
197 *
198 * The basis of the hash algorithm was taken from an idea sent by email to the
199 * IEEE Posix P1003.2 mailing list from Phong Vo (kpv@research.att.com) and
200 * Glenn Fowler (gsf@research.att.com).  Landon Curt Noll (chongo@toad.com)
201 * later improved on their algorithm.
202 *
203 * The magic is in the interesting relationship between the special prime
204 * 16777619 (2^24 + 403) and 2^32 and 2^8.
205 *
206 * This hash produces the fewest collisions of any function that we've seen so
207 * far, and works well on both numbers and strings.
208 *
209 * PUBLIC: u_int32_t __ham_func5 __P((const void *, u_int32_t));
210 */
211u_int32_t
212__ham_func5(key, len)
213	const void *key;
214	u_int32_t len;
215{
216	const u_int8_t *k, *e;
217        u_int32_t h;
218
219	k = key;
220	e = k + len;
221        for (h = 0; k < e; ++k) {
222                h *= 16777619;
223                h ^= *k;
224        }
225        return (h);
226}
227