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 8.1 (Berkeley) 6/4/93"; 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 int hash1 __P((u_char *, int)); 49 static int hash2 __P((u_char *, int)); 50 static int hash3 __P((u_char *, int)); 51 static int hash4 __P((u_char *, int)); 52 53 /* Global default hash function */ 54 int (*__default_hash) __P((u_char *, int)) = hash4; 55 56 /******************************* HASH FUNCTIONS **************************/ 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 * This came from ejb's hsearch. 62 */ 63 64 #define PRIME1 37 65 #define PRIME2 1048583 66 67 static int 68 hash1(key, len) 69 register u_char *key; 70 register int len; 71 { 72 register int h; 73 74 h = 0; 75 /* Convert string to integer */ 76 while (len--) 77 h = h * PRIME1 ^ (*key++ - ' '); 78 h %= PRIME2; 79 return (h); 80 } 81 82 /* 83 * Phong's linear congruential hash 84 */ 85 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c)) 86 87 static int 88 hash2(key, len) 89 register u_char *key; 90 int len; 91 { 92 register u_char *e, c; 93 register int h; 94 95 e = key + len; 96 for (h = 0; key != e;) { 97 c = *key++; 98 if (!c && key > 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 * OZ's original sdbm hash 113 */ 114 static int 115 hash3(key, len) 116 register u_char *key; 117 register int len; 118 { 119 register int n, loop; 120 121 #define HASHC n = *key++ + 65599 * n 122 123 n = 0; 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 } 151 152 /* Hash function from Chris Torek. */ 153 static int 154 hash4(key, len) 155 register u_char *key; 156 register int len; 157 { 158 register int h, loop; 159 160 #define HASH4a h = (h << 5) - h + *key++; 161 #define HASH4b h = (h << 5) + h + *key++; 162 #define HASH4 HASH4b 163 164 h = 0; 165 if (len > 0) { 166 loop = (len + 8 - 1) >> 3; 167 168 switch (len & (8 - 1)) { 169 case 0: 170 do { /* All fall throughs */ 171 HASH4; 172 case 7: 173 HASH4; 174 case 6: 175 HASH4; 176 case 5: 177 HASH4; 178 case 4: 179 HASH4; 180 case 3: 181 HASH4; 182 case 2: 183 HASH4; 184 case 1: 185 HASH4; 186 } while (--loop); 187 } 188 189 } 190 return (h); 191 } 192