hash_func.c revision 1.7
1 /* $NetBSD: hash_func.c,v 1.7 1997/07/13 18:52:05 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. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 */ 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 1.7 1997/07/13 18:52:05 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 static u_int32_t hash1 __P((const void *, size_t)) __attribute__((__unused__)); 56 static u_int32_t hash2 __P((const void *, size_t)) __attribute__((__unused__)); 57 static u_int32_t hash3 __P((const void *, size_t)) __attribute__((__unused__)); 58 static u_int32_t hash4 __P((const void *, size_t)) __attribute__((__unused__)); 59 60 /* Global default hash function */ 61 u_int32_t (*__default_hash) __P((const void *, size_t)) = hash4; 62 63 /* 64 * HASH FUNCTIONS 65 * 66 * Assume that we've already split the bucket to which this key hashes, 67 * calculate that bucket, and check that in fact we did already split it. 68 * 69 * This came from ejb's hsearch. 70 */ 71 72 #define PRIME1 37 73 #define PRIME2 1048583 74 75 static u_int32_t 76 hash1(keyarg, len) 77 const void *keyarg; 78 register size_t len; 79 { 80 register const u_char *key; 81 register 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(keyarg, len) 97 const void *keyarg; 98 size_t len; 99 { 100 register const u_char *e, *key; 101 register u_int32_t h; 102 register u_char c; 103 104 key = keyarg; 105 e = key + len; 106 for (h = 0; key != e;) { 107 c = *key++; 108 if (!c && key > e) 109 break; 110 dcharhash(h, c); 111 } 112 return (h); 113 } 114 115 /* 116 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte 117 * units. On the first time through the loop we get the "leftover bytes" 118 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle 119 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If 120 * this routine is heavily used enough, it's worth the ugly coding. 121 * 122 * OZ's original sdbm hash 123 */ 124 static u_int32_t 125 hash3(keyarg, len) 126 const void *keyarg; 127 register size_t len; 128 { 129 register const u_char *key; 130 register size_t loop; 131 register u_int32_t h; 132 133 #define HASHC h = *key++ + 65599 * h 134 135 h = 0; 136 key = keyarg; 137 if (len > 0) { 138 loop = (len + 8 - 1) >> 3; 139 140 switch (len & (8 - 1)) { 141 case 0: 142 do { 143 HASHC; 144 /* FALLTHROUGH */ 145 case 7: 146 HASHC; 147 /* FALLTHROUGH */ 148 case 6: 149 HASHC; 150 /* FALLTHROUGH */ 151 case 5: 152 HASHC; 153 /* FALLTHROUGH */ 154 case 4: 155 HASHC; 156 /* FALLTHROUGH */ 157 case 3: 158 HASHC; 159 /* FALLTHROUGH */ 160 case 2: 161 HASHC; 162 /* FALLTHROUGH */ 163 case 1: 164 HASHC; 165 } while (--loop); 166 } 167 } 168 return (h); 169 } 170 171 /* Hash function from Chris Torek. */ 172 static u_int32_t 173 hash4(keyarg, len) 174 const void *keyarg; 175 register size_t len; 176 { 177 register const u_char *key; 178 register size_t loop; 179 register u_int32_t h; 180 181 #define HASH4a h = (h << 5) - h + *key++; 182 #define HASH4b h = (h << 5) + h + *key++; 183 #define HASH4 HASH4b 184 185 h = 0; 186 key = keyarg; 187 if (len > 0) { 188 loop = (len + 8 - 1) >> 3; 189 190 switch (len & (8 - 1)) { 191 case 0: 192 do { 193 HASH4; 194 /* FALLTHROUGH */ 195 case 7: 196 HASH4; 197 /* FALLTHROUGH */ 198 case 6: 199 HASH4; 200 /* FALLTHROUGH */ 201 case 5: 202 HASH4; 203 /* FALLTHROUGH */ 204 case 4: 205 HASH4; 206 /* FALLTHROUGH */ 207 case 3: 208 HASH4; 209 /* FALLTHROUGH */ 210 case 2: 211 HASH4; 212 /* FALLTHROUGH */ 213 case 1: 214 HASH4; 215 } while (--loop); 216 } 217 } 218 return (h); 219 } 220
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