1 /* $NetBSD: hash_func.c,v 1.13 2008/09/10 17:52:35 joerg Exp $ */
2
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 HAVE_NBTOOL_CONFIG_H
36 #include "nbtool_config.h"
37 #endif
38
39 #include <sys/cdefs.h>
40 __RCSID("$NetBSD: hash_func.c,v 1.13 2008/09/10 17:52:35 joerg Exp $");
41
42 #include <sys/types.h>
43
44 #include <db.h>
45 #include "hash.h"
46 #include "page.h"
47 #include "extern.h"
48
49 #if 0
50 static uint32_t hash1(const void *, size_t) __attribute__((__unused__));
51 static uint32_t hash2(const void *, size_t) __attribute__((__unused__));
52 static uint32_t hash3(const void *, size_t) __attribute__((__unused__));
53 #endif
54 static uint32_t hash4(const void *, size_t) __attribute__((__unused__));
55
56 /* Global default hash function */
57 uint32_t (*__default_hash)(const void *, size_t) = hash4;
58 #if 0
59 /*
60 * HASH FUNCTIONS
61 *
62 * Assume that we've already split the bucket to which this key hashes,
63 * calculate that bucket, and check that in fact we did already split it.
64 *
65 * This came from ejb's hsearch.
66 */
67
68 #define PRIME1 37
69 #define PRIME2 1048583
70
71 static uint32_t
72 hash1(const void *keyarg, size_t len)
73 {
74 const uint8_t *key;
75 uint32_t h;
76
77 /* Convert string to integer */
78 for (key = keyarg, h = 0; len--;)
79 h = h * PRIME1 ^ (*key++ - ' ');
80 h %= PRIME2;
81 return (h);
82 }
83
84 /*
85 * Phong's linear congruential hash
86 */
87 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
88
89 static uint32_t
90 hash2(const void *keyarg, size_t len)
91 {
92 const uint8_t *e, *key;
93 uint32_t h;
94 uint8_t c;
95
96 key = keyarg;
97 e = key + len;
98 for (h = 0; key != e;) {
99 c = *key++;
100 if (!c && key > e)
101 break;
102 dcharhash(h, c);
103 }
104 return (h);
105 }
106
107 /*
108 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte
109 * units. On the first time through the loop we get the "leftover bytes"
110 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle
111 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If
112 * this routine is heavily used enough, it's worth the ugly coding.
113 *
114 * OZ's original sdbm hash
115 */
116 static uint32_t
117 hash3(const void *keyarg, size_t len)
118 {
119 const uint8_t *key;
120 size_t loop;
121 uint32_t h;
122
123 #define HASHC h = *key++ + 65599 * h
124
125 h = 0;
126 key = keyarg;
127 if (len > 0) {
128 loop = (len + 8 - 1) >> 3;
129
130 switch (len & (8 - 1)) {
131 case 0:
132 do {
133 HASHC;
134 /* FALLTHROUGH */
135 case 7:
136 HASHC;
137 /* FALLTHROUGH */
138 case 6:
139 HASHC;
140 /* FALLTHROUGH */
141 case 5:
142 HASHC;
143 /* FALLTHROUGH */
144 case 4:
145 HASHC;
146 /* FALLTHROUGH */
147 case 3:
148 HASHC;
149 /* FALLTHROUGH */
150 case 2:
151 HASHC;
152 /* FALLTHROUGH */
153 case 1:
154 HASHC;
155 } while (--loop);
156 }
157 }
158 return (h);
159 }
160 #endif
161
162 /* Hash function from Chris Torek. */
163 static uint32_t
hash4(const void * keyarg,size_t len)164 hash4(const void *keyarg, size_t len)
165 {
166 const uint8_t *key;
167 size_t loop;
168 uint32_t h;
169
170 #define HASH4a h = (h << 5) - h + *key++;
171 #define HASH4b h = (h << 5) + h + *key++;
172 #define HASH4 HASH4b
173
174 h = 0;
175 key = keyarg;
176 if (len > 0) {
177 loop = (len + 8 - 1) >> 3;
178
179 switch (len & (8 - 1)) {
180 case 0:
181 do {
182 HASH4;
183 /* FALLTHROUGH */
184 case 7:
185 HASH4;
186 /* FALLTHROUGH */
187 case 6:
188 HASH4;
189 /* FALLTHROUGH */
190 case 5:
191 HASH4;
192 /* FALLTHROUGH */
193 case 4:
194 HASH4;
195 /* FALLTHROUGH */
196 case 3:
197 HASH4;
198 /* FALLTHROUGH */
199 case 2:
200 HASH4;
201 /* FALLTHROUGH */
202 case 1:
203 HASH4;
204 } while (--loop);
205 }
206 }
207 return (h);
208 }
209