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 * 4. Neither the name of the University nor the names of its contributors
17 * may be used to endorse or promote products derived from this software
18 * without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 */
32
33 #if defined(LIBC_SCCS) && !defined(lint)
34 static char sccsid[] = "@(#)hash_func.c 8.2 (Berkeley) 2/21/94";
35 #endif /* LIBC_SCCS and not lint */
36 #include <sys/cdefs.h>
37 __FBSDID("$FreeBSD$");
38
39 #include <sys/types.h>
40
41 #include <db.h>
42 #include "hash.h"
43 #include "page.h"
44 #include "extern.h"
45
46 #ifdef notdef
47 static u_int32_t hash1(const void *, size_t) __unused;
48 static u_int32_t hash2(const void *, size_t) __unused;
49 static u_int32_t hash3(const void *, size_t) __unused;
50 #endif
51 static u_int32_t hash4(const void *, size_t);
52
53 /* Default hash function. */
54 u_int32_t (*__default_hash)(const void *, size_t) = hash4;
55
56 #ifdef notdef
57 /*
58 * Assume that we've already split the bucket to which this key hashes,
59 * calculate that bucket, and check that in fact we did already split it.
60 *
61 * EJB's original hsearch hash.
62 */
63 #define PRIME1 37
64 #define PRIME2 1048583
65
66 u_int32_t
hash1(const void * key,size_t len)67 hash1(const void *key, 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 u_int32_t
hash2(const void * key,size_t len)87 hash2(const void *key, size_t len)
88 {
89 u_int32_t h;
90 u_int8_t *e, c, *k;
91
92 k = (u_int8_t *)key;
93 e = k + len;
94 for (h = 0; k != e;) {
95 c = *k++;
96 if (!c && k > e)
97 break;
98 dcharhash(h, c);
99 }
100 return (h);
101 }
102
103 /*
104 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte
105 * units. On the first time through the loop we get the "leftover bytes"
106 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle
107 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If
108 * this routine is heavily used enough, it's worth the ugly coding.
109 *
110 * Ozan Yigit's original sdbm hash.
111 */
112 u_int32_t
hash3(const void * key,size_t len)113 hash3(const void *key, size_t len)
114 {
115 u_int32_t n, loop;
116 u_int8_t *k;
117
118 #define HASHC n = *k++ + 65599 * n
119
120 n = 0;
121 k = (u_int8_t *)key;
122 if (len > 0) {
123 loop = (len + 8 - 1) >> 3;
124
125 switch (len & (8 - 1)) {
126 case 0:
127 do { /* All fall throughs */
128 HASHC;
129 case 7:
130 HASHC;
131 case 6:
132 HASHC;
133 case 5:
134 HASHC;
135 case 4:
136 HASHC;
137 case 3:
138 HASHC;
139 case 2:
140 HASHC;
141 case 1:
142 HASHC;
143 } while (--loop);
144 }
145
146 }
147 return (n);
148 }
149 #endif /* notdef */
150
151 /* Chris Torek's hash function. */
152 u_int32_t
hash4(const void * key,size_t len)153 hash4(const void *key, size_t len)
154 {
155 u_int32_t h, loop;
156 const u_int8_t *k;
157
158 #define HASH4a h = (h << 5) - h + *k++;
159 #define HASH4b h = (h << 5) + h + *k++;
160 #define HASH4 HASH4b
161
162 h = 0;
163 k = key;
164 if (len > 0) {
165 loop = (len + 8 - 1) >> 3;
166
167 switch (len & (8 - 1)) {
168 case 0:
169 do { /* All fall throughs */
170 HASH4;
171 case 7:
172 HASH4;
173 case 6:
174 HASH4;
175 case 5:
176 HASH4;
177 case 4:
178 HASH4;
179 case 3:
180 HASH4;
181 case 2:
182 HASH4;
183 case 1:
184 HASH4;
185 } while (--loop);
186 }
187
188 }
189 return (h);
190 }
191