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. Neither the name of the University nor the names of its contributors 17 * may be used to endorse or promote products derived from this software 18 * without specific prior written permission. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 */ 32 33 #if defined(LIBC_SCCS) && !defined(lint) 34 static char sccsid[] = "@(#)hash_func.c 8.2 (Berkeley) 2/21/94"; 35 #endif /* LIBC_SCCS and not lint */ 36 #include <sys/cdefs.h> 37 __FBSDID("$FreeBSD$"); 38 39 #include <sys/types.h> 40 41 #include <db.h> 42 #include "hash.h" 43 #include "page.h" 44 #include "extern.h" 45 46 #ifdef notdef 47 static u_int32_t hash1(const void *, size_t) __unused; 48 static u_int32_t hash2(const void *, size_t) __unused; 49 static u_int32_t hash3(const void *, size_t) __unused; 50 #endif 51 static u_int32_t hash4(const void *, size_t); 52 53 /* Default hash function. */ 54 u_int32_t (*__default_hash)(const void *, size_t) = hash4; 55 56 #ifdef notdef 57 /* 58 * Assume that we've already split the bucket to which this key hashes, 59 * calculate that bucket, and check that in fact we did already split it. 60 * 61 * EJB's original hsearch hash. 62 */ 63 #define PRIME1 37 64 #define PRIME2 1048583 65 66 u_int32_t 67 hash1(const void *key, size_t len) 68 { 69 u_int32_t h; 70 u_int8_t *k; 71 72 h = 0; 73 k = (u_int8_t *)key; 74 /* Convert string to integer */ 75 while (len--) 76 h = h * PRIME1 ^ (*k++ - ' '); 77 h %= PRIME2; 78 return (h); 79 } 80 81 /* 82 * Phong Vo's linear congruential hash 83 */ 84 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c)) 85 86 u_int32_t 87 hash2(const void *key, size_t len) 88 { 89 u_int32_t h; 90 u_int8_t *e, c, *k; 91 92 k = (u_int8_t *)key; 93 e = k + len; 94 for (h = 0; k != e;) { 95 c = *k++; 96 if (!c && k > e) 97 break; 98 dcharhash(h, c); 99 } 100 return (h); 101 } 102 103 /* 104 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte 105 * units. On the first time through the loop we get the "leftover bytes" 106 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle 107 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If 108 * this routine is heavily used enough, it's worth the ugly coding. 109 * 110 * Ozan Yigit's original sdbm hash. 111 */ 112 u_int32_t 113 hash3(const void *key, size_t len) 114 { 115 u_int32_t n, loop; 116 u_int8_t *k; 117 118 #define HASHC n = *k++ + 65599 * n 119 120 n = 0; 121 k = (u_int8_t *)key; 122 if (len > 0) { 123 loop = (len + 8 - 1) >> 3; 124 125 switch (len & (8 - 1)) { 126 case 0: 127 do { /* All fall throughs */ 128 HASHC; 129 case 7: 130 HASHC; 131 case 6: 132 HASHC; 133 case 5: 134 HASHC; 135 case 4: 136 HASHC; 137 case 3: 138 HASHC; 139 case 2: 140 HASHC; 141 case 1: 142 HASHC; 143 } while (--loop); 144 } 145 146 } 147 return (n); 148 } 149 #endif /* notdef */ 150 151 /* Chris Torek's hash function. */ 152 u_int32_t 153 hash4(const void *key, size_t len) 154 { 155 u_int32_t h, loop; 156 const u_int8_t *k; 157 158 #define HASH4a h = (h << 5) - h + *k++; 159 #define HASH4b h = (h << 5) + h + *k++; 160 #define HASH4 HASH4b 161 162 h = 0; 163 k = key; 164 if (len > 0) { 165 loop = (len + 8 - 1) >> 3; 166 167 switch (len & (8 - 1)) { 168 case 0: 169 do { /* All fall throughs */ 170 HASH4; 171 case 7: 172 HASH4; 173 case 6: 174 HASH4; 175 case 5: 176 HASH4; 177 case 4: 178 HASH4; 179 case 3: 180 HASH4; 181 case 2: 182 HASH4; 183 case 1: 184 HASH4; 185 } while (--loop); 186 } 187 188 } 189 return (h); 190 } 191