hash_func.c revision 1.9
1 /* $NetBSD: hash_func.c,v 1.9 2003/08/07 16:42:42 agc 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 #include <sys/cdefs.h> 36 #if defined(LIBC_SCCS) && !defined(lint) 37 #if 0 38 static char sccsid[] = "@(#)hash_func.c 8.2 (Berkeley) 2/21/94"; 39 #else 40 __RCSID("$NetBSD: hash_func.c,v 1.9 2003/08/07 16:42:42 agc Exp $"); 41 #endif 42 #endif /* LIBC_SCCS and not lint */ 43 44 #include <sys/types.h> 45 46 #include <db.h> 47 #include "hash.h" 48 #include "page.h" 49 #include "extern.h" 50 51 #if 0 52 static u_int32_t hash1 __P((const void *, size_t)) __attribute__((__unused__)); 53 static u_int32_t hash2 __P((const void *, size_t)) __attribute__((__unused__)); 54 static u_int32_t hash3 __P((const void *, size_t)) __attribute__((__unused__)); 55 #endif 56 static u_int32_t hash4 __P((const void *, size_t)) __attribute__((__unused__)); 57 58 /* Global default hash function */ 59 u_int32_t (*__default_hash) __P((const void *, size_t)) = hash4; 60 #if 0 61 /* 62 * HASH FUNCTIONS 63 * 64 * Assume that we've already split the bucket to which this key hashes, 65 * calculate that bucket, and check that in fact we did already split it. 66 * 67 * This came from ejb's hsearch. 68 */ 69 70 #define PRIME1 37 71 #define PRIME2 1048583 72 73 static u_int32_t 74 hash1(keyarg, len) 75 const void *keyarg; 76 register size_t len; 77 { 78 register const u_char *key; 79 register u_int32_t h; 80 81 /* Convert string to integer */ 82 for (key = keyarg, h = 0; len--;) 83 h = h * PRIME1 ^ (*key++ - ' '); 84 h %= PRIME2; 85 return (h); 86 } 87 88 /* 89 * Phong's linear congruential hash 90 */ 91 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c)) 92 93 static u_int32_t 94 hash2(keyarg, len) 95 const void *keyarg; 96 size_t len; 97 { 98 register const u_char *e, *key; 99 register u_int32_t h; 100 register 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(keyarg, len) 124 const void *keyarg; 125 register size_t len; 126 { 127 register const u_char *key; 128 register size_t loop; 129 register u_int32_t h; 130 131 #define HASHC h = *key++ + 65599 * h 132 133 h = 0; 134 key = keyarg; 135 if (len > 0) { 136 loop = (len + 8 - 1) >> 3; 137 138 switch (len & (8 - 1)) { 139 case 0: 140 do { 141 HASHC; 142 /* FALLTHROUGH */ 143 case 7: 144 HASHC; 145 /* FALLTHROUGH */ 146 case 6: 147 HASHC; 148 /* FALLTHROUGH */ 149 case 5: 150 HASHC; 151 /* FALLTHROUGH */ 152 case 4: 153 HASHC; 154 /* FALLTHROUGH */ 155 case 3: 156 HASHC; 157 /* FALLTHROUGH */ 158 case 2: 159 HASHC; 160 /* FALLTHROUGH */ 161 case 1: 162 HASHC; 163 } while (--loop); 164 } 165 } 166 return (h); 167 } 168 #endif 169 170 /* Hash function from Chris Torek. */ 171 static u_int32_t 172 hash4(keyarg, len) 173 const void *keyarg; 174 register size_t len; 175 { 176 register const u_char *key; 177 register size_t loop; 178 register u_int32_t h; 179 180 #define HASH4a h = (h << 5) - h + *key++; 181 #define HASH4b h = (h << 5) + h + *key++; 182 #define HASH4 HASH4b 183 184 h = 0; 185 key = keyarg; 186 if (len > 0) { 187 loop = (len + 8 - 1) >> 3; 188 189 switch (len & (8 - 1)) { 190 case 0: 191 do { 192 HASH4; 193 /* FALLTHROUGH */ 194 case 7: 195 HASH4; 196 /* FALLTHROUGH */ 197 case 6: 198 HASH4; 199 /* FALLTHROUGH */ 200 case 5: 201 HASH4; 202 /* FALLTHROUGH */ 203 case 4: 204 HASH4; 205 /* FALLTHROUGH */ 206 case 3: 207 HASH4; 208 /* FALLTHROUGH */ 209 case 2: 210 HASH4; 211 /* FALLTHROUGH */ 212 case 1: 213 HASH4; 214 } while (--loop); 215 } 216 } 217 return (h); 218 } 219
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