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 #include <sys/types.h>
38
39 #include "db-int.h"
40 #include "hash.h"
41 #include "page.h"
42 #include "extern.h"
43
44 #if 0
45 static u_int32_t hash1 __P((const void *, size_t));
46 static u_int32_t hash2 __P((const void *, size_t));
47 static u_int32_t hash3 __P((const void *, size_t));
48 #endif
49 static u_int32_t hash4 __P((const void *, size_t));
50
51 /* Default hash function. */
52 u_int32_t (*__default_hash) __P((const void *, size_t)) = hash4;
53
54 /*
55 * Assume that we've already split the bucket to which this key hashes,
56 * calculate that bucket, and check that in fact we did already split it.
57 *
58 * EJB's original hsearch hash.
59 */
60 #define PRIME1 37
61 #define PRIME2 1048583
62
63 #if 0
64 static u_int32_t
65 hash1(key, len)
66 const void *key;
67 size_t len;
68 {
69 u_int32_t h;
70 u_int8_t *k;
71
72 h = 0;
73 k = (u_int8_t *)key;
74 /* Convert string to integer */
75 while (len--)
76 h = h * PRIME1 ^ (*k++ - ' ');
77 h %= PRIME2;
78 return (h);
79 }
80
81 /*
82 * Phong Vo's linear congruential hash
83 */
84 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
85
86 static u_int32_t
87 hash2(key, len)
88 const void *key;
89 size_t len;
90 {
91 u_int32_t h;
92 u_int8_t *e, c, *k;
93
94 k = (u_int8_t *)key;
95 e = k + len;
96 for (h = 0; k != e;) {
97 c = *k++;
98 if (!c && k > e)
99 break;
100 dcharhash(h, c);
101 }
102 return (h);
103 }
104
105 /*
106 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte
107 * units. On the first time through the loop we get the "leftover bytes"
108 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle
109 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If
110 * this routine is heavily used enough, it's worth the ugly coding.
111 *
112 * Ozan Yigit's original sdbm hash.
113 */
114 static u_int32_t
115 hash3(key, len)
116 const void *key;
117 size_t len;
118 {
119 u_int32_t n, loop;
120 u_int8_t *k;
121
122 #define HASHC n = *k++ + 65599 * n
123
124 n = 0;
125 k = (u_int8_t *)key;
126 if (len > 0) {
127 loop = (len + 8 - 1) >> 3;
128
129 switch (len & (8 - 1)) {
130 case 0:
131 do { /* All fall throughs */
132 HASHC;
133 case 7:
134 HASHC;
135 case 6:
136 HASHC;
137 case 5:
138 HASHC;
139 case 4:
140 HASHC;
141 case 3:
142 HASHC;
143 case 2:
144 HASHC;
145 case 1:
146 HASHC;
147 } while (--loop);
148 }
149
150 }
151 return (n);
152 }
153 #endif
154
155
156 /* Chris Torek's hash function. */
157 static u_int32_t
hash4(const void * key,size_t len)158 hash4(const void *key, size_t len)
159 {
160 u_int32_t h, loop;
161 const u_int8_t *k;
162
163 #define HASH4a h = (h << 5) - h + *k++;
164 #define HASH4b h = (h << 5) + h + *k++;
165 #define HASH4 HASH4b
166
167 h = 0;
168 k = (const u_int8_t *)key;
169 if (len > 0) {
170 loop = (len + 8 - 1) >> 3;
171
172 switch (len & (8 - 1)) {
173 case 0:
174 do { /* All fall throughs */
175 HASH4;
176 /* FALLTHROUGH */
177 case 7:
178 HASH4;
179 /* FALLTHROUGH */
180 case 6:
181 HASH4;
182 /* FALLTHROUGH */
183 case 5:
184 HASH4;
185 /* FALLTHROUGH */
186 case 4:
187 HASH4;
188 /* FALLTHROUGH */
189 case 3:
190 HASH4;
191 /* FALLTHROUGH */
192 case 2:
193 HASH4;
194 /* FALLTHROUGH */
195 case 1:
196 HASH4;
197 } while (--loop);
198 }
199
200 }
201 return (h);
202 }
203