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