1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
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 #if defined(LIBC_SCCS) && !defined(lint)
36 static char sccsid[] = "@(#)hash_func.c 8.2 (Berkeley) 2/21/94";
37 #endif /* LIBC_SCCS and not lint */
38 #include <sys/cdefs.h>
39 __FBSDID("$FreeBSD$");
40
41 #include <sys/types.h>
42
43 #include <db.h>
44 #include "hash.h"
45 #include "page.h"
46 #include "extern.h"
47
48 #ifdef notdef
49 static u_int32_t hash1(const void *, size_t) __unused;
50 static u_int32_t hash2(const void *, size_t) __unused;
51 static u_int32_t hash3(const void *, size_t) __unused;
52 #endif
53 static u_int32_t hash4(const void *, size_t);
54
55 /* Default hash function. */
56 u_int32_t (*__default_hash)(const void *, size_t) = hash4;
57
58 #ifdef notdef
59 /*
60 * Assume that we've already split the bucket to which this key hashes,
61 * calculate that bucket, and check that in fact we did already split it.
62 *
63 * EJB's original hsearch hash.
64 */
65 #define PRIME1 37
66 #define PRIME2 1048583
67
68 u_int32_t
hash1(const void * key,size_t len)69 hash1(const void *key, size_t len)
70 {
71 u_int32_t h;
72 u_int8_t *k;
73
74 h = 0;
75 k = (u_int8_t *)key;
76 /* Convert string to integer */
77 while (len--)
78 h = h * PRIME1 ^ (*k++ - ' ');
79 h %= PRIME2;
80 return (h);
81 }
82
83 /*
84 * Phong Vo's linear congruential hash
85 */
86 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
87
88 u_int32_t
hash2(const void * key,size_t len)89 hash2(const void *key, 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 u_int32_t
hash3(const void * key,size_t len)115 hash3(const void *key, size_t len)
116 {
117 u_int32_t n, loop;
118 u_int8_t *k;
119
120 #define HASHC n = *k++ + 65599 * n
121
122 n = 0;
123 k = (u_int8_t *)key;
124 if (len > 0) {
125 loop = (len + 8 - 1) >> 3;
126
127 switch (len & (8 - 1)) {
128 case 0:
129 do { /* All fall throughs */
130 HASHC;
131 case 7:
132 HASHC;
133 case 6:
134 HASHC;
135 case 5:
136 HASHC;
137 case 4:
138 HASHC;
139 case 3:
140 HASHC;
141 case 2:
142 HASHC;
143 case 1:
144 HASHC;
145 } while (--loop);
146 }
147
148 }
149 return (n);
150 }
151 #endif /* notdef */
152
153 /* Chris Torek's hash function. */
154 u_int32_t
hash4(const void * key,size_t len)155 hash4(const void *key, size_t len)
156 {
157 u_int32_t h, loop;
158 const u_int8_t *k;
159
160 #define HASH4a h = (h << 5) - h + *k++;
161 #define HASH4b h = (h << 5) + h + *k++;
162 #define HASH4 HASH4b
163
164 h = 0;
165 k = key;
166 if (len > 0) {
167 loop = (len + 8 - 1) >> 3;
168
169 switch (len & (8 - 1)) {
170 case 0:
171 do { /* All fall throughs */
172 HASH4;
173 case 7:
174 HASH4;
175 case 6:
176 HASH4;
177 case 5:
178 HASH4;
179 case 4:
180 HASH4;
181 case 3:
182 HASH4;
183 case 2:
184 HASH4;
185 case 1:
186 HASH4;
187 } while (--loop);
188 }
189
190 }
191 return (h);
192 }
193