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)
38 static char sccsid[] = "@(#)hash_func.c 8.4 (Berkeley) 11/7/95";
39 #endif /* LIBC_SCCS and not lint */
40
41 #include <sys/types.h>
42
43 #include "db-int.h"
44 #include "hash.h"
45 #include "page.h"
46 #include "extern.h"
47
48 #if 0
49 static u_int32_t hash1 __P((const void *, size_t));
50 static u_int32_t hash2 __P((const void *, size_t));
51 static u_int32_t hash3 __P((const void *, size_t));
52 #endif
53 static u_int32_t hash4 __P((const void *, size_t));
54
55 /* Default hash function. */
56 u_int32_t (*__default_hash) __P((const void *, size_t)) = hash4;
57
58 /*
59 * Assume that we've already split the bucket to which this key hashes,
60 * calculate that bucket, and check that in fact we did already split it.
61 *
62 * EJB's original hsearch hash.
63 */
64 #define PRIME1 37
65 #define PRIME2 1048583
66
67 #if 0
68 static u_int32_t
69 hash1(key, len)
70 const void *key;
71 size_t len;
72 {
73 u_int32_t h;
74 u_int8_t *k;
75
76 h = 0;
77 k = (u_int8_t *)key;
78 /* Convert string to integer */
79 while (len--)
80 h = h * PRIME1 ^ (*k++ - ' ');
81 h %= PRIME2;
82 return (h);
83 }
84
85 /*
86 * Phong Vo's linear congruential hash
87 */
88 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
89
90 static u_int32_t
91 hash2(key, len)
92 const void *key;
93 size_t len;
94 {
95 u_int32_t h;
96 u_int8_t *e, c, *k;
97
98 k = (u_int8_t *)key;
99 e = k + len;
100 for (h = 0; k != e;) {
101 c = *k++;
102 if (!c && k > e)
103 break;
104 dcharhash(h, c);
105 }
106 return (h);
107 }
108
109 /*
110 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte
111 * units. On the first time through the loop we get the "leftover bytes"
112 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle
113 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If
114 * this routine is heavily used enough, it's worth the ugly coding.
115 *
116 * Ozan Yigit's original sdbm hash.
117 */
118 static u_int32_t
119 hash3(key, len)
120 const void *key;
121 size_t len;
122 {
123 u_int32_t n, loop;
124 u_int8_t *k;
125
126 #define HASHC n = *k++ + 65599 * n
127
128 n = 0;
129 k = (u_int8_t *)key;
130 if (len > 0) {
131 loop = (len + 8 - 1) >> 3;
132
133 switch (len & (8 - 1)) {
134 case 0:
135 do { /* All fall throughs */
136 HASHC;
137 case 7:
138 HASHC;
139 case 6:
140 HASHC;
141 case 5:
142 HASHC;
143 case 4:
144 HASHC;
145 case 3:
146 HASHC;
147 case 2:
148 HASHC;
149 case 1:
150 HASHC;
151 } while (--loop);
152 }
153
154 }
155 return (n);
156 }
157 #endif
158
159
160 /* Chris Torek's hash function. */
161 static u_int32_t
hash4(key,len)162 hash4(key, len)
163 const void *key;
164 size_t len;
165 {
166 u_int32_t h, loop;
167 const u_int8_t *k;
168
169 #define HASH4a h = (h << 5) - h + *k++;
170 #define HASH4b h = (h << 5) + h + *k++;
171 #define HASH4 HASH4b
172
173 h = 0;
174 k = (const u_int8_t *)key;
175 if (len > 0) {
176 loop = (len + 8 - 1) >> 3;
177
178 switch (len & (8 - 1)) {
179 case 0:
180 do { /* All fall throughs */
181 HASH4;
182 case 7:
183 HASH4;
184 case 6:
185 HASH4;
186 case 5:
187 HASH4;
188 case 4:
189 HASH4;
190 case 3:
191 HASH4;
192 case 2:
193 HASH4;
194 case 1:
195 HASH4;
196 } while (--loop);
197 }
198
199 }
200 return (h);
201 }
202