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 #include <sys/types.h> 36 37 #include <db.h> 38 #include "hash.h" 39 #include "page.h" 40 #include "extern.h" 41 42 #ifdef notdef 43 static u_int32_t hash1(const void *, size_t) __unused; 44 static u_int32_t hash2(const void *, size_t) __unused; 45 static u_int32_t hash3(const void *, size_t) __unused; 46 #endif 47 static u_int32_t hash4(const void *, size_t); 48 49 /* Default hash function. */ 50 u_int32_t (*__default_hash)(const void *, size_t) = hash4; 51 52 #ifdef notdef 53 /* 54 * Assume that we've already split the bucket to which this key hashes, 55 * calculate that bucket, and check that in fact we did already split it. 56 * 57 * EJB's original hsearch hash. 58 */ 59 #define PRIME1 37 60 #define PRIME2 1048583 61 62 u_int32_t 63 hash1(const void *key, size_t len) 64 { 65 u_int32_t h; 66 u_int8_t *k; 67 68 h = 0; 69 k = (u_int8_t *)key; 70 /* Convert string to integer */ 71 while (len--) 72 h = h * PRIME1 ^ (*k++ - ' '); 73 h %= PRIME2; 74 return (h); 75 } 76 77 /* 78 * Phong Vo's linear congruential hash 79 */ 80 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c)) 81 82 u_int32_t 83 hash2(const void *key, size_t len) 84 { 85 u_int32_t h; 86 u_int8_t *e, c, *k; 87 88 k = (u_int8_t *)key; 89 e = k + len; 90 for (h = 0; k != e;) { 91 c = *k++; 92 if (!c && k > e) 93 break; 94 dcharhash(h, c); 95 } 96 return (h); 97 } 98 99 /* 100 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte 101 * units. On the first time through the loop we get the "leftover bytes" 102 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle 103 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If 104 * this routine is heavily used enough, it's worth the ugly coding. 105 * 106 * Ozan Yigit's original sdbm hash. 107 */ 108 u_int32_t 109 hash3(const void *key, size_t len) 110 { 111 u_int32_t n, loop; 112 u_int8_t *k; 113 114 #define HASHC n = *k++ + 65599 * n 115 116 n = 0; 117 k = (u_int8_t *)key; 118 if (len > 0) { 119 loop = (len + 8 - 1) >> 3; 120 121 switch (len & (8 - 1)) { 122 case 0: 123 do { /* All fall throughs */ 124 HASHC; 125 case 7: 126 HASHC; 127 case 6: 128 HASHC; 129 case 5: 130 HASHC; 131 case 4: 132 HASHC; 133 case 3: 134 HASHC; 135 case 2: 136 HASHC; 137 case 1: 138 HASHC; 139 } while (--loop); 140 } 141 142 } 143 return (n); 144 } 145 #endif /* notdef */ 146 147 /* Chris Torek's hash function. */ 148 u_int32_t 149 hash4(const void *key, size_t len) 150 { 151 u_int32_t h, loop; 152 const u_int8_t *k; 153 154 #define HASH4a h = (h << 5) - h + *k++; 155 #define HASH4b h = (h << 5) + h + *k++; 156 #define HASH4 HASH4b 157 158 h = 0; 159 k = key; 160 if (len > 0) { 161 loop = (len + 8 - 1) >> 3; 162 163 switch (len & (8 - 1)) { 164 case 0: 165 do { /* All fall throughs */ 166 HASH4; 167 case 7: 168 HASH4; 169 case 6: 170 HASH4; 171 case 5: 172 HASH4; 173 case 4: 174 HASH4; 175 case 3: 176 HASH4; 177 case 2: 178 HASH4; 179 case 1: 180 HASH4; 181 } while (--loop); 182 } 183 184 } 185 return (h); 186 } 187