1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 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 #if defined(LIBC_SCCS) && !defined(lint) 36 static char sccsid[] = "@(#)hash_func.c 8.2 (Berkeley) 2/21/94"; 37 #endif /* LIBC_SCCS and not lint */ 38 #include <sys/cdefs.h> 39 __FBSDID("$FreeBSD$"); 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 #ifdef notdef 49 static u_int32_t hash1(const void *, size_t) __unused; 50 static u_int32_t hash2(const void *, size_t) __unused; 51 static u_int32_t hash3(const void *, size_t) __unused; 52 #endif 53 static u_int32_t hash4(const void *, size_t); 54 55 /* Default hash function. */ 56 u_int32_t (*__default_hash)(const void *, size_t) = hash4; 57 58 #ifdef notdef 59 /* 60 * Assume that we've already split the bucket to which this key hashes, 61 * calculate that bucket, and check that in fact we did already split it. 62 * 63 * EJB's original hsearch hash. 64 */ 65 #define PRIME1 37 66 #define PRIME2 1048583 67 68 u_int32_t 69 hash1(const void *key, size_t len) 70 { 71 u_int32_t h; 72 u_int8_t *k; 73 74 h = 0; 75 k = (u_int8_t *)key; 76 /* Convert string to integer */ 77 while (len--) 78 h = h * PRIME1 ^ (*k++ - ' '); 79 h %= PRIME2; 80 return (h); 81 } 82 83 /* 84 * Phong Vo's linear congruential hash 85 */ 86 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c)) 87 88 u_int32_t 89 hash2(const void *key, size_t len) 90 { 91 u_int32_t h; 92 u_int8_t *e, c, *k; 93 94 k = (u_int8_t *)key; 95 e = k + len; 96 for (h = 0; k != e;) { 97 c = *k++; 98 if (!c && k > e) 99 break; 100 dcharhash(h, c); 101 } 102 return (h); 103 } 104 105 /* 106 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte 107 * units. On the first time through the loop we get the "leftover bytes" 108 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle 109 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If 110 * this routine is heavily used enough, it's worth the ugly coding. 111 * 112 * Ozan Yigit's original sdbm hash. 113 */ 114 u_int32_t 115 hash3(const void *key, size_t len) 116 { 117 u_int32_t n, loop; 118 u_int8_t *k; 119 120 #define HASHC n = *k++ + 65599 * n 121 122 n = 0; 123 k = (u_int8_t *)key; 124 if (len > 0) { 125 loop = (len + 8 - 1) >> 3; 126 127 switch (len & (8 - 1)) { 128 case 0: 129 do { /* All fall throughs */ 130 HASHC; 131 case 7: 132 HASHC; 133 case 6: 134 HASHC; 135 case 5: 136 HASHC; 137 case 4: 138 HASHC; 139 case 3: 140 HASHC; 141 case 2: 142 HASHC; 143 case 1: 144 HASHC; 145 } while (--loop); 146 } 147 148 } 149 return (n); 150 } 151 #endif /* notdef */ 152 153 /* Chris Torek's hash function. */ 154 u_int32_t 155 hash4(const void *key, size_t len) 156 { 157 u_int32_t h, loop; 158 const u_int8_t *k; 159 160 #define HASH4a h = (h << 5) - h + *k++; 161 #define HASH4b h = (h << 5) + h + *k++; 162 #define HASH4 HASH4b 163 164 h = 0; 165 k = key; 166 if (len > 0) { 167 loop = (len + 8 - 1) >> 3; 168 169 switch (len & (8 - 1)) { 170 case 0: 171 do { /* All fall throughs */ 172 HASH4; 173 case 7: 174 HASH4; 175 case 6: 176 HASH4; 177 case 5: 178 HASH4; 179 case 4: 180 HASH4; 181 case 3: 182 HASH4; 183 case 2: 184 HASH4; 185 case 1: 186 HASH4; 187 } while (--loop); 188 } 189 190 } 191 return (h); 192 } 193