hash_func.c revision 165903 
1/*-
2 * Copyright (c) 1990, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Margo Seltzer.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 * 4. Neither the name of the University nor the names of its contributors
17 *    may be used to endorse or promote products derived from this software
18 *    without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 */
32
33#if defined(LIBC_SCCS) && !defined(lint)
34static char sccsid[] = "@(#)hash_func.c	8.2 (Berkeley) 2/21/94";
35#endif /* LIBC_SCCS and not lint */
36#include <sys/cdefs.h>
37__FBSDID("$FreeBSD: head/lib/libc/db/hash/hash_func.c 165903 2007-01-09 00:28:16Z imp $");
38
39#include <sys/types.h>
40
41#include <db.h>
42#include "hash.h"
43#include "page.h"
44#include "extern.h"
45
46static u_int32_t hash1(const void *, size_t) __unused;
47static u_int32_t hash2(const void *, size_t) __unused;
48static u_int32_t hash3(const void *, size_t) __unused;
49static u_int32_t hash4(const void *, size_t);
50
51/* Global default hash function */
52u_int32_t (*__default_hash)(const void *, size_t) = hash4;
53
54/*
55 * HASH FUNCTIONS
56 *
57 * Assume that we've already split the bucket to which this key hashes,
58 * calculate that bucket, and check that in fact we did already split it.
59 *
60 * This came from ejb's hsearch.
61 */
62
63#define PRIME1		37
64#define PRIME2		1048583
65
66static u_int32_t
67hash1(keyarg, len)
68	const void *keyarg;
69	size_t len;
70{
71	const u_char *key;
72	u_int32_t h;
73
74	/* Convert string to integer */
75	for (key = keyarg, h = 0; len--;)
76		h = h * PRIME1 ^ (*key++ - ' ');
77	h %= PRIME2;
78	return (h);
79}
80
81/*
82 * Phong's linear congruential hash
83 */
84#define dcharhash(h, c)	((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
85
86static u_int32_t
87hash2(keyarg, len)
88	const void *keyarg;
89	size_t len;
90{
91	const u_char *e, *key;
92	u_int32_t h;
93	u_char c;
94
95	key = keyarg;
96	e = key + len;
97	for (h = 0; key != e;) {
98		c = *key++;
99		if (!c && key > e)
100			break;
101		dcharhash(h, c);
102	}
103	return (h);
104}
105
106/*
107 * This is INCREDIBLY ugly, but fast.  We break the string up into 8 byte
108 * units.  On the first time through the loop we get the "leftover bytes"
109 * (strlen % 8).  On every other iteration, we perform 8 HASHC's so we handle
110 * all 8 bytes.  Essentially, this saves us 7 cmp & branch instructions.  If
111 * this routine is heavily used enough, it's worth the ugly coding.
112 *
113 * OZ's original sdbm hash
114 */
115static u_int32_t
116hash3(keyarg, len)
117	const void *keyarg;
118	size_t len;
119{
120	const u_char *key;
121	size_t loop;
122	u_int32_t h;
123
124#define HASHC   h = *key++ + 65599 * h
125
126	h = 0;
127	key = keyarg;
128	if (len > 0) {
129		loop = (len + 8 - 1) >> 3;
130
131		switch (len & (8 - 1)) {
132		case 0:
133			do {
134				HASHC;
135				/* FALLTHROUGH */
136		case 7:
137				HASHC;
138				/* FALLTHROUGH */
139		case 6:
140				HASHC;
141				/* FALLTHROUGH */
142		case 5:
143				HASHC;
144				/* FALLTHROUGH */
145		case 4:
146				HASHC;
147				/* FALLTHROUGH */
148		case 3:
149				HASHC;
150				/* FALLTHROUGH */
151		case 2:
152				HASHC;
153				/* FALLTHROUGH */
154		case 1:
155				HASHC;
156			} while (--loop);
157		}
158	}
159	return (h);
160}
161
162/* Hash function from Chris Torek. */
163static u_int32_t
164hash4(keyarg, len)
165	const void *keyarg;
166	size_t len;
167{
168	const u_char *key;
169	size_t loop;
170	u_int32_t h;
171
172#define HASH4a   h = (h << 5) - h + *key++;
173#define HASH4b   h = (h << 5) + h + *key++;
174#define HASH4 HASH4b
175
176	h = 0;
177	key = keyarg;
178	if (len > 0) {
179		loop = (len + 8 - 1) >> 3;
180
181		switch (len & (8 - 1)) {
182		case 0:
183			do {
184				HASH4;
185				/* FALLTHROUGH */
186		case 7:
187				HASH4;
188				/* FALLTHROUGH */
189		case 6:
190				HASH4;
191				/* FALLTHROUGH */
192		case 5:
193				HASH4;
194				/* FALLTHROUGH */
195		case 4:
196				HASH4;
197				/* FALLTHROUGH */
198		case 3:
199				HASH4;
200				/* FALLTHROUGH */
201		case 2:
202				HASH4;
203				/* FALLTHROUGH */
204		case 1:
205				HASH4;
206			} while (--loop);
207		}
208	}
209	return (h);
210}
211