hash_func.c revision 1.9 1 /* $NetBSD: hash_func.c,v 1.9 2003/08/07 16:42:42 agc Exp $ */
2
3 /*-
4 * Copyright (c) 1990, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Margo Seltzer.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the University nor the names of its contributors
19 * may be used to endorse or promote products derived from this software
20 * without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35 #include <sys/cdefs.h>
36 #if defined(LIBC_SCCS) && !defined(lint)
37 #if 0
38 static char sccsid[] = "@(#)hash_func.c 8.2 (Berkeley) 2/21/94";
39 #else
40 __RCSID("$NetBSD: hash_func.c,v 1.9 2003/08/07 16:42:42 agc Exp $");
41 #endif
42 #endif /* LIBC_SCCS and not lint */
43
44 #include <sys/types.h>
45
46 #include <db.h>
47 #include "hash.h"
48 #include "page.h"
49 #include "extern.h"
50
51 #if 0
52 static u_int32_t hash1 __P((const void *, size_t)) __attribute__((__unused__));
53 static u_int32_t hash2 __P((const void *, size_t)) __attribute__((__unused__));
54 static u_int32_t hash3 __P((const void *, size_t)) __attribute__((__unused__));
55 #endif
56 static u_int32_t hash4 __P((const void *, size_t)) __attribute__((__unused__));
57
58 /* Global default hash function */
59 u_int32_t (*__default_hash) __P((const void *, size_t)) = hash4;
60 #if 0
61 /*
62 * HASH FUNCTIONS
63 *
64 * Assume that we've already split the bucket to which this key hashes,
65 * calculate that bucket, and check that in fact we did already split it.
66 *
67 * This came from ejb's hsearch.
68 */
69
70 #define PRIME1 37
71 #define PRIME2 1048583
72
73 static u_int32_t
74 hash1(keyarg, len)
75 const void *keyarg;
76 register size_t len;
77 {
78 register const u_char *key;
79 register u_int32_t h;
80
81 /* Convert string to integer */
82 for (key = keyarg, h = 0; len--;)
83 h = h * PRIME1 ^ (*key++ - ' ');
84 h %= PRIME2;
85 return (h);
86 }
87
88 /*
89 * Phong's linear congruential hash
90 */
91 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
92
93 static u_int32_t
94 hash2(keyarg, len)
95 const void *keyarg;
96 size_t len;
97 {
98 register const u_char *e, *key;
99 register u_int32_t h;
100 register u_char c;
101
102 key = keyarg;
103 e = key + len;
104 for (h = 0; key != e;) {
105 c = *key++;
106 if (!c && key > e)
107 break;
108 dcharhash(h, c);
109 }
110 return (h);
111 }
112
113 /*
114 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte
115 * units. On the first time through the loop we get the "leftover bytes"
116 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle
117 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If
118 * this routine is heavily used enough, it's worth the ugly coding.
119 *
120 * OZ's original sdbm hash
121 */
122 static u_int32_t
123 hash3(keyarg, len)
124 const void *keyarg;
125 register size_t len;
126 {
127 register const u_char *key;
128 register size_t loop;
129 register u_int32_t h;
130
131 #define HASHC h = *key++ + 65599 * h
132
133 h = 0;
134 key = keyarg;
135 if (len > 0) {
136 loop = (len + 8 - 1) >> 3;
137
138 switch (len & (8 - 1)) {
139 case 0:
140 do {
141 HASHC;
142 /* FALLTHROUGH */
143 case 7:
144 HASHC;
145 /* FALLTHROUGH */
146 case 6:
147 HASHC;
148 /* FALLTHROUGH */
149 case 5:
150 HASHC;
151 /* FALLTHROUGH */
152 case 4:
153 HASHC;
154 /* FALLTHROUGH */
155 case 3:
156 HASHC;
157 /* FALLTHROUGH */
158 case 2:
159 HASHC;
160 /* FALLTHROUGH */
161 case 1:
162 HASHC;
163 } while (--loop);
164 }
165 }
166 return (h);
167 }
168 #endif
169
170 /* Hash function from Chris Torek. */
171 static u_int32_t
172 hash4(keyarg, len)
173 const void *keyarg;
174 register size_t len;
175 {
176 register const u_char *key;
177 register size_t loop;
178 register u_int32_t h;
179
180 #define HASH4a h = (h << 5) - h + *key++;
181 #define HASH4b h = (h << 5) + h + *key++;
182 #define HASH4 HASH4b
183
184 h = 0;
185 key = keyarg;
186 if (len > 0) {
187 loop = (len + 8 - 1) >> 3;
188
189 switch (len & (8 - 1)) {
190 case 0:
191 do {
192 HASH4;
193 /* FALLTHROUGH */
194 case 7:
195 HASH4;
196 /* FALLTHROUGH */
197 case 6:
198 HASH4;
199 /* FALLTHROUGH */
200 case 5:
201 HASH4;
202 /* FALLTHROUGH */
203 case 4:
204 HASH4;
205 /* FALLTHROUGH */
206 case 3:
207 HASH4;
208 /* FALLTHROUGH */
209 case 2:
210 HASH4;
211 /* FALLTHROUGH */
212 case 1:
213 HASH4;
214 } while (--loop);
215 }
216 }
217 return (h);
218 }
219