hash_func.c revision 1.4
1 /*- 2 * Copyright (c) 1990, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This code is derived from software contributed to Berkeley by 6 * Margo Seltzer. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. All advertising materials mentioning features or use of this software 17 * must display the following acknowledgement: 18 * This product includes software developed by the University of 19 * California, Berkeley and its contributors. 20 * 4. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 */ 36 37 #if defined(LIBC_SCCS) && !defined(lint) 38 static char sccsid[] = "@(#)hash_func.c 8.2 (Berkeley) 2/21/94"; 39 #endif /* LIBC_SCCS and not lint */ 40 41 #include <sys/types.h> 42 43 #include <db.h> 44 #include "hash.h" 45 #include "page.h" 46 #include "extern.h" 47 48 static u_int32_t hash1 __P((const void *, size_t)); 49 static u_int32_t hash2 __P((const void *, size_t)); 50 static u_int32_t hash3 __P((const void *, size_t)); 51 static u_int32_t hash4 __P((const void *, size_t)); 52 53 /* Global default hash function */ 54 u_int32_t (*__default_hash) __P((const void *, size_t)) = hash4; 55 56 /* 57 * HASH FUNCTIONS 58 * 59 * Assume that we've already split the bucket to which this key hashes, 60 * calculate that bucket, and check that in fact we did already split it. 61 * 62 * This came from ejb's hsearch. 63 */ 64 65 #define PRIME1 37 66 #define PRIME2 1048583 67 68 static u_int32_t 69 hash1(keyarg, len) 70 const void *keyarg; 71 register size_t len; 72 { 73 register const u_char *key; 74 register u_int32_t h; 75 76 /* Convert string to integer */ 77 for (key = keyarg, h = 0; len--;) 78 h = h * PRIME1 ^ (*key++ - ' '); 79 h %= PRIME2; 80 return (h); 81 } 82 83 /* 84 * Phong's linear congruential hash 85 */ 86 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c)) 87 88 static u_int32_t 89 hash2(keyarg, len) 90 const void *keyarg; 91 size_t len; 92 { 93 register const u_char *e, *key; 94 register u_int32_t h; 95 register u_char c; 96 97 key = keyarg; 98 e = key + len; 99 for (h = 0; key != e;) { 100 c = *key++; 101 if (!c && key > e) 102 break; 103 dcharhash(h, c); 104 } 105 return (h); 106 } 107 108 /* 109 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte 110 * units. On the first time through the loop we get the "leftover bytes" 111 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle 112 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If 113 * this routine is heavily used enough, it's worth the ugly coding. 114 * 115 * OZ's original sdbm hash 116 */ 117 static u_int32_t 118 hash3(keyarg, len) 119 const void *keyarg; 120 register size_t len; 121 { 122 register const u_char *key; 123 register size_t loop; 124 register u_int32_t h; 125 126 #define HASHC h = *key++ + 65599 * h 127 128 h = 0; 129 key = keyarg; 130 if (len > 0) { 131 loop = (len + 8 - 1) >> 3; 132 133 switch (len & (8 - 1)) { 134 case 0: 135 do { 136 HASHC; 137 /* FALLTHROUGH */ 138 case 7: 139 HASHC; 140 /* FALLTHROUGH */ 141 case 6: 142 HASHC; 143 /* FALLTHROUGH */ 144 case 5: 145 HASHC; 146 /* FALLTHROUGH */ 147 case 4: 148 HASHC; 149 /* FALLTHROUGH */ 150 case 3: 151 HASHC; 152 /* FALLTHROUGH */ 153 case 2: 154 HASHC; 155 /* FALLTHROUGH */ 156 case 1: 157 HASHC; 158 } while (--loop); 159 } 160 } 161 return (h); 162 } 163 164 /* Hash function from Chris Torek. */ 165 static u_int32_t 166 hash4(keyarg, len) 167 const void *keyarg; 168 register size_t len; 169 { 170 register const u_char *key; 171 register size_t loop; 172 register u_int32_t h; 173 174 #define HASH4a h = (h << 5) - h + *key++; 175 #define HASH4b h = (h << 5) + h + *key++; 176 #define HASH4 HASH4b 177 178 h = 0; 179 key = keyarg; 180 if (len > 0) { 181 loop = (len + 8 - 1) >> 3; 182 183 switch (len & (8 - 1)) { 184 case 0: 185 do { 186 HASH4; 187 /* FALLTHROUGH */ 188 case 7: 189 HASH4; 190 /* FALLTHROUGH */ 191 case 6: 192 HASH4; 193 /* FALLTHROUGH */ 194 case 5: 195 HASH4; 196 /* FALLTHROUGH */ 197 case 4: 198 HASH4; 199 /* FALLTHROUGH */ 200 case 3: 201 HASH4; 202 /* FALLTHROUGH */ 203 case 2: 204 HASH4; 205 /* FALLTHROUGH */ 206 case 1: 207 HASH4; 208 } while (--loop); 209 } 210 } 211 return (h); 212 } 213
Indexes created Wed Sep 24 22:09:59 GMT 2025