1 #pragma ident "%Z%%M% %I% %E% SMI" 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 #if defined(LIBC_SCCS) && !defined(lint) 40 static char sccsid[] = "@(#)hash_func.c 8.4 (Berkeley) 11/7/95"; 41 #endif /* LIBC_SCCS and not lint */ 42 43 #include <sys/types.h> 44 45 #include "db-int.h" 46 #include "hash.h" 47 #include "page.h" 48 #include "extern.h" 49 50 #if 0 51 static u_int32_t hash1 __P((const void *, size_t)); 52 static u_int32_t hash2 __P((const void *, size_t)); 53 static u_int32_t hash3 __P((const void *, size_t)); 54 #endif 55 static u_int32_t hash4 __P((const void *, size_t)); 56 57 /* Default hash function. */ 58 u_int32_t (*__default_hash) __P((const void *, size_t)) = hash4; 59 60 /* 61 * Assume that we've already split the bucket to which this key hashes, 62 * calculate that bucket, and check that in fact we did already split it. 63 * 64 * EJB's original hsearch hash. 65 */ 66 #define PRIME1 37 67 #define PRIME2 1048583 68 69 #if 0 70 static u_int32_t 71 hash1(key, len) 72 const void *key; 73 size_t len; 74 { 75 u_int32_t h; 76 u_int8_t *k; 77 78 h = 0; 79 k = (u_int8_t *)key; 80 /* Convert string to integer */ 81 while (len--) 82 h = h * PRIME1 ^ (*k++ - ' '); 83 h %= PRIME2; 84 return (h); 85 } 86 87 /* 88 * Phong Vo's linear congruential hash 89 */ 90 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c)) 91 92 static u_int32_t 93 hash2(key, len) 94 const void *key; 95 size_t len; 96 { 97 u_int32_t h; 98 u_int8_t *e, c, *k; 99 100 k = (u_int8_t *)key; 101 e = k + len; 102 for (h = 0; k != e;) { 103 c = *k++; 104 if (!c && k > e) 105 break; 106 dcharhash(h, c); 107 } 108 return (h); 109 } 110 111 /* 112 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte 113 * units. On the first time through the loop we get the "leftover bytes" 114 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle 115 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If 116 * this routine is heavily used enough, it's worth the ugly coding. 117 * 118 * Ozan Yigit's original sdbm hash. 119 */ 120 static u_int32_t 121 hash3(key, len) 122 const void *key; 123 size_t len; 124 { 125 u_int32_t n, loop; 126 u_int8_t *k; 127 128 #define HASHC n = *k++ + 65599 * n 129 130 n = 0; 131 k = (u_int8_t *)key; 132 if (len > 0) { 133 loop = (len + 8 - 1) >> 3; 134 135 switch (len & (8 - 1)) { 136 case 0: 137 do { /* All fall throughs */ 138 HASHC; 139 case 7: 140 HASHC; 141 case 6: 142 HASHC; 143 case 5: 144 HASHC; 145 case 4: 146 HASHC; 147 case 3: 148 HASHC; 149 case 2: 150 HASHC; 151 case 1: 152 HASHC; 153 } while (--loop); 154 } 155 156 } 157 return (n); 158 } 159 #endif 160 161 162 /* Chris Torek's hash function. */ 163 static u_int32_t 164 hash4(key, len) 165 const void *key; 166 size_t len; 167 { 168 u_int32_t h, loop; 169 const u_int8_t *k; 170 171 #define HASH4a h = (h << 5) - h + *k++; 172 #define HASH4b h = (h << 5) + h + *k++; 173 #define HASH4 HASH4b 174 175 h = 0; 176 k = (const u_int8_t *)key; 177 if (len > 0) { 178 loop = (len + 8 - 1) >> 3; 179 180 switch (len & (8 - 1)) { 181 case 0: 182 do { /* All fall throughs */ 183 HASH4; 184 case 7: 185 HASH4; 186 case 6: 187 HASH4; 188 case 5: 189 HASH4; 190 case 4: 191 HASH4; 192 case 3: 193 HASH4; 194 case 2: 195 HASH4; 196 case 1: 197 HASH4; 198 } while (--loop); 199 } 200 201 } 202 return (h); 203 } 204