hash_func.c revision 1.11
1 /* $NetBSD: hash_func.c,v 1.11 2007/02/03 23:46:09 christos 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 #if defined(LIBC_SCCS) && !defined(lint) 41 #if 0 42 static char sccsid[] = "@(#)hash_func.c 8.2 (Berkeley) 2/21/94"; 43 #else 44 __RCSID("$NetBSD: hash_func.c,v 1.11 2007/02/03 23:46:09 christos Exp $"); 45 #endif 46 #endif /* LIBC_SCCS and not lint */ 47 48 #include <sys/types.h> 49 50 #include <db.h> 51 #include "hash.h" 52 #include "page.h" 53 #include "extern.h" 54 55 #if 0 56 static u_int32_t hash1(const void *, size_t) __attribute__((__unused__)); 57 static u_int32_t hash2(const void *, size_t) __attribute__((__unused__)); 58 static u_int32_t hash3(const void *, size_t) __attribute__((__unused__)); 59 #endif 60 static u_int32_t hash4(const void *, size_t) __attribute__((__unused__)); 61 62 /* Global default hash function */ 63 u_int32_t (*__default_hash)(const void *, size_t) = hash4; 64 #if 0 65 /* 66 * HASH FUNCTIONS 67 * 68 * Assume that we've already split the bucket to which this key hashes, 69 * calculate that bucket, and check that in fact we did already split it. 70 * 71 * This came from ejb's hsearch. 72 */ 73 74 #define PRIME1 37 75 #define PRIME2 1048583 76 77 static u_int32_t 78 hash1(const void *keyarg, size_t len) 79 { 80 const u_char *key; 81 u_int32_t h; 82 83 /* Convert string to integer */ 84 for (key = keyarg, h = 0; len--;) 85 h = h * PRIME1 ^ (*key++ - ' '); 86 h %= PRIME2; 87 return (h); 88 } 89 90 /* 91 * Phong's linear congruential hash 92 */ 93 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c)) 94 95 static u_int32_t 96 hash2(const void *keyarg, size_t len) 97 { 98 const u_char *e, *key; 99 u_int32_t h; 100 u_char c; 101 102 key = keyarg; 103 e = key + len; 104 for (h = 0; key != e;) { 105 c = *key++; 106 if (!c && key > e) 107 break; 108 dcharhash(h, c); 109 } 110 return (h); 111 } 112 113 /* 114 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte 115 * units. On the first time through the loop we get the "leftover bytes" 116 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle 117 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If 118 * this routine is heavily used enough, it's worth the ugly coding. 119 * 120 * OZ's original sdbm hash 121 */ 122 static u_int32_t 123 hash3(const void *keyarg, size_t len) 124 { 125 const u_char *key; 126 size_t loop; 127 u_int32_t h; 128 129 #define HASHC h = *key++ + 65599 * h 130 131 h = 0; 132 key = keyarg; 133 if (len > 0) { 134 loop = (len + 8 - 1) >> 3; 135 136 switch (len & (8 - 1)) { 137 case 0: 138 do { 139 HASHC; 140 /* FALLTHROUGH */ 141 case 7: 142 HASHC; 143 /* FALLTHROUGH */ 144 case 6: 145 HASHC; 146 /* FALLTHROUGH */ 147 case 5: 148 HASHC; 149 /* FALLTHROUGH */ 150 case 4: 151 HASHC; 152 /* FALLTHROUGH */ 153 case 3: 154 HASHC; 155 /* FALLTHROUGH */ 156 case 2: 157 HASHC; 158 /* FALLTHROUGH */ 159 case 1: 160 HASHC; 161 } while (--loop); 162 } 163 } 164 return (h); 165 } 166 #endif 167 168 /* Hash function from Chris Torek. */ 169 static u_int32_t 170 hash4(const void *keyarg, size_t len) 171 { 172 const u_char *key; 173 size_t loop; 174 u_int32_t h; 175 176 #define HASH4a h = (h << 5) - h + *key++; 177 #define HASH4b h = (h << 5) + h + *key++; 178 #define HASH4 HASH4b 179 180 h = 0; 181 key = keyarg; 182 if (len > 0) { 183 loop = (len + 8 - 1) >> 3; 184 185 switch (len & (8 - 1)) { 186 case 0: 187 do { 188 HASH4; 189 /* FALLTHROUGH */ 190 case 7: 191 HASH4; 192 /* FALLTHROUGH */ 193 case 6: 194 HASH4; 195 /* FALLTHROUGH */ 196 case 5: 197 HASH4; 198 /* FALLTHROUGH */ 199 case 4: 200 HASH4; 201 /* FALLTHROUGH */ 202 case 3: 203 HASH4; 204 /* FALLTHROUGH */ 205 case 2: 206 HASH4; 207 /* FALLTHROUGH */ 208 case 1: 209 HASH4; 210 } while (--loop); 211 } 212 } 213 return (h); 214 } 215
Indexes created Thu Sep 25 02:09:54 GMT 2025