hash_func.c revision 92905 
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 * 3. All advertising materials mentioning features or use of this software
17 *    must display the following acknowledgement:
18 *	This product includes software developed by the University of
19 *	California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 *    may be used to endorse or promote products derived from this software
22 *    without specific prior written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 */
36
37#if defined(LIBC_SCCS) && !defined(lint)
38static char sccsid[] = "@(#)hash_func.c	8.2 (Berkeley) 2/21/94";
39#endif /* LIBC_SCCS and not lint */
40#include <sys/cdefs.h>
41__FBSDID("$FreeBSD: head/lib/libc/db/hash/hash_func.c 92905 2002-03-21 22:49:10Z obrien $");
42
43#include <sys/types.h>
44
45#include <db.h>
46#include "hash.h"
47#include "page.h"
48#include "extern.h"
49
50static u_int32_t hash1(const void *, size_t);
51static u_int32_t hash2(const void *, size_t);
52static u_int32_t hash3(const void *, size_t);
53static u_int32_t hash4(const void *, size_t);
54
55/* Global default hash function */
56u_int32_t (*__default_hash) __P((const void *, size_t)) = hash4;
57
58/*
59 * HASH FUNCTIONS
60 *
61 * Assume that we've already split the bucket to which this key hashes,
62 * calculate that bucket, and check that in fact we did already split it.
63 *
64 * This came from ejb's hsearch.
65 */
66
67#define PRIME1		37
68#define PRIME2		1048583
69
70static u_int32_t
71hash1(keyarg, len)
72	const void *keyarg;
73	size_t len;
74{
75	const u_char *key;
76	u_int32_t h;
77
78	/* Convert string to integer */
79	for (key = keyarg, h = 0; len--;)
80		h = h * PRIME1 ^ (*key++ - ' ');
81	h %= PRIME2;
82	return (h);
83}
84
85/*
86 * Phong's linear congruential hash
87 */
88#define dcharhash(h, c)	((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
89
90static u_int32_t
91hash2(keyarg, len)
92	const void *keyarg;
93	size_t len;
94{
95	const u_char *e, *key;
96	u_int32_t h;
97	u_char c;
98
99	key = keyarg;
100	e = key + len;
101	for (h = 0; key != e;) {
102		c = *key++;
103		if (!c && key > e)
104			break;
105		dcharhash(h, c);
106	}
107	return (h);
108}
109
110/*
111 * This is INCREDIBLY ugly, but fast.  We break the string up into 8 byte
112 * units.  On the first time through the loop we get the "leftover bytes"
113 * (strlen % 8).  On every other iteration, we perform 8 HASHC's so we handle
114 * all 8 bytes.  Essentially, this saves us 7 cmp & branch instructions.  If
115 * this routine is heavily used enough, it's worth the ugly coding.
116 *
117 * OZ's original sdbm hash
118 */
119static u_int32_t
120hash3(keyarg, len)
121	const void *keyarg;
122	size_t len;
123{
124	const u_char *key;
125	size_t loop;
126	u_int32_t h;
127
128#define HASHC   h = *key++ + 65599 * h
129
130	h = 0;
131	key = keyarg;
132	if (len > 0) {
133		loop = (len + 8 - 1) >> 3;
134
135		switch (len & (8 - 1)) {
136		case 0:
137			do {
138				HASHC;
139				/* FALLTHROUGH */
140		case 7:
141				HASHC;
142				/* FALLTHROUGH */
143		case 6:
144				HASHC;
145				/* FALLTHROUGH */
146		case 5:
147				HASHC;
148				/* FALLTHROUGH */
149		case 4:
150				HASHC;
151				/* FALLTHROUGH */
152		case 3:
153				HASHC;
154				/* FALLTHROUGH */
155		case 2:
156				HASHC;
157				/* FALLTHROUGH */
158		case 1:
159				HASHC;
160			} while (--loop);
161		}
162	}
163	return (h);
164}
165
166/* Hash function from Chris Torek. */
167static u_int32_t
168hash4(keyarg, len)
169	const void *keyarg;
170	size_t len;
171{
172	const u_char *key;
173	size_t loop;
174	u_int32_t h;
175
176#define HASH4a   h = (h << 5) - h + *key++;
177#define HASH4b   h = (h << 5) + h + *key++;
178#define HASH4 HASH4b
179
180	h = 0;
181	key = keyarg;
182	if (len > 0) {
183		loop = (len + 8 - 1) >> 3;
184
185		switch (len & (8 - 1)) {
186		case 0:
187			do {
188				HASH4;
189				/* FALLTHROUGH */
190		case 7:
191				HASH4;
192				/* FALLTHROUGH */
193		case 6:
194				HASH4;
195				/* FALLTHROUGH */
196		case 5:
197				HASH4;
198				/* FALLTHROUGH */
199		case 4:
200				HASH4;
201				/* FALLTHROUGH */
202		case 3:
203				HASH4;
204				/* FALLTHROUGH */
205		case 2:
206				HASH4;
207				/* FALLTHROUGH */
208		case 1:
209				HASH4;
210			} while (--loop);
211		}
212	}
213	return (h);
214}
215