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 8.2 (Berkeley) 2/21/94";
39 #endif /* LIBC_SCCS and not lint */
40 #include <sys/cdefs.h>
41 #include <sys/types.h>
42
43 #include "db_local.h"
44 #include "hash.h"
45 #include "page.h"
46 #include "extern.h"
47
48 static __uint32_t hash1(const void *, size_t);
49 static __uint32_t hash2(const void *, size_t);
50 static __uint32_t hash3(const void *, size_t);
51 static __uint32_t hash4(const void *, size_t);
52
53 /* Global default hash function */
54 __uint32_t (*__default_hash)(const void *, size_t) = hash4;
55
56 /*
57 * HASH FUNCTIONS
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 * This came from ejb's hsearch.
63 */
64
65 #define PRIME1 37
66 #define PRIME2 1048583
67
68 static __uint32_t
hash1(keyarg,len)69 hash1(keyarg, len)
70 const void *keyarg;
71 size_t len;
72 {
73 const u_char *key;
74 __uint32_t h;
75
76 /* Convert string to integer */
77 for (key = keyarg, h = 0; len--;)
78 h = h * PRIME1 ^ (*key++ - ' ');
79 h %= PRIME2;
80 return (h);
81 }
82
83 /*
84 * Phong's linear congruential hash
85 */
86 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
87
88 static __uint32_t
hash2(keyarg,len)89 hash2(keyarg, len)
90 const void *keyarg;
91 size_t len;
92 {
93 const u_char *e, *key;
94 __uint32_t h;
95 u_char c;
96
97 key = keyarg;
98 e = key + len;
99 for (h = 0; key != e;) {
100 c = *key++;
101 if (!c && key > e)
102 break;
103 dcharhash(h, c);
104 }
105 return (h);
106 }
107
108 /*
109 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte
110 * units. On the first time through the loop we get the "leftover bytes"
111 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle
112 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If
113 * this routine is heavily used enough, it's worth the ugly coding.
114 *
115 * OZ's original sdbm hash
116 */
117 static __uint32_t
hash3(keyarg,len)118 hash3(keyarg, len)
119 const void *keyarg;
120 size_t len;
121 {
122 const u_char *key;
123 size_t loop;
124 __uint32_t h;
125
126 #define HASHC h = *key++ + 65599 * h
127
128 h = 0;
129 key = keyarg;
130 if (len > 0) {
131 loop = (len + 8 - 1) >> 3;
132
133 switch (len & (8 - 1)) {
134 case 0:
135 do {
136 HASHC;
137 /* FALLTHROUGH */
138 case 7:
139 HASHC;
140 /* FALLTHROUGH */
141 case 6:
142 HASHC;
143 /* FALLTHROUGH */
144 case 5:
145 HASHC;
146 /* FALLTHROUGH */
147 case 4:
148 HASHC;
149 /* FALLTHROUGH */
150 case 3:
151 HASHC;
152 /* FALLTHROUGH */
153 case 2:
154 HASHC;
155 /* FALLTHROUGH */
156 case 1:
157 HASHC;
158 } while (--loop);
159 }
160 }
161 return (h);
162 }
163
164 /* Hash function from Chris Torek. */
165 static __uint32_t
hash4(keyarg,len)166 hash4(keyarg, len)
167 const void *keyarg;
168 size_t len;
169 {
170 const u_char *key;
171 size_t loop;
172 __uint32_t h;
173
174 #define HASH4a h = (h << 5) - h + *key++;
175 #define HASH4b h = (h << 5) + h + *key++;
176 #define HASH4 HASH4b
177
178 h = 0;
179 key = keyarg;
180 if (len > 0) {
181 loop = (len + 8 - 1) >> 3;
182
183 switch (len & (8 - 1)) {
184 case 0:
185 do {
186 HASH4;
187 /* FALLTHROUGH */
188 case 7:
189 HASH4;
190 /* FALLTHROUGH */
191 case 6:
192 HASH4;
193 /* FALLTHROUGH */
194 case 5:
195 HASH4;
196 /* FALLTHROUGH */
197 case 4:
198 HASH4;
199 /* FALLTHROUGH */
200 case 3:
201 HASH4;
202 /* FALLTHROUGH */
203 case 2:
204 HASH4;
205 /* FALLTHROUGH */
206 case 1:
207 HASH4;
208 } while (--loop);
209 }
210 }
211 return (h);
212 }
213