hash_func.c revision 92889
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) 38static char sccsid[] = "@(#)hash_func.c 8.2 (Berkeley) 2/21/94"; 39#endif /* LIBC_SCCS and not lint */ 40#include <sys/cdefs.h> 41__FBSDID("$FreeBSD: head/lib/libc/db/hash/hash_func.c 92889 2002-03-21 18:49:23Z obrien $"); 42 43#include <sys/types.h> 44 45#include <db.h> 46#include "hash.h" 47#include "page.h" 48#include "extern.h" 49 50static u_int32_t hash1 __P((const void *, size_t)); 51static u_int32_t hash2 __P((const void *, size_t)); 52static u_int32_t hash3 __P((const void *, size_t)); 53static u_int32_t hash4 __P((const void *, size_t)); 54 55/* Global default hash function */ 56u_int32_t (*__default_hash) __P((const void *, size_t)) = hash4; 57 58/* 59 * HASH FUNCTIONS 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 * This came from ejb's hsearch. 65 */ 66 67#define PRIME1 37 68#define PRIME2 1048583 69 70static u_int32_t 71hash1(keyarg, len) 72 const void *keyarg; 73 size_t len; 74{ 75 const u_char *key; 76 u_int32_t h; 77 78 /* Convert string to integer */ 79 for (key = keyarg, h = 0; len--;) 80 h = h * PRIME1 ^ (*key++ - ' '); 81 h %= PRIME2; 82 return (h); 83} 84 85/* 86 * Phong's linear congruential hash 87 */ 88#define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c)) 89 90static u_int32_t 91hash2(keyarg, len) 92 const void *keyarg; 93 size_t len; 94{ 95 const u_char *e, *key; 96 u_int32_t h; 97 u_char c; 98 99 key = keyarg; 100 e = key + len; 101 for (h = 0; key != e;) { 102 c = *key++; 103 if (!c && key > e) 104 break; 105 dcharhash(h, c); 106 } 107 return (h); 108} 109 110/* 111 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte 112 * units. On the first time through the loop we get the "leftover bytes" 113 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle 114 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If 115 * this routine is heavily used enough, it's worth the ugly coding. 116 * 117 * OZ's original sdbm hash 118 */ 119static u_int32_t 120hash3(keyarg, len) 121 const void *keyarg; 122 size_t len; 123{ 124 const u_char *key; 125 size_t loop; 126 u_int32_t h; 127 128#define HASHC h = *key++ + 65599 * h 129 130 h = 0; 131 key = keyarg; 132 if (len > 0) { 133 loop = (len + 8 - 1) >> 3; 134 135 switch (len & (8 - 1)) { 136 case 0: 137 do { 138 HASHC; 139 /* FALLTHROUGH */ 140 case 7: 141 HASHC; 142 /* FALLTHROUGH */ 143 case 6: 144 HASHC; 145 /* FALLTHROUGH */ 146 case 5: 147 HASHC; 148 /* FALLTHROUGH */ 149 case 4: 150 HASHC; 151 /* FALLTHROUGH */ 152 case 3: 153 HASHC; 154 /* FALLTHROUGH */ 155 case 2: 156 HASHC; 157 /* FALLTHROUGH */ 158 case 1: 159 HASHC; 160 } while (--loop); 161 } 162 } 163 return (h); 164} 165 166/* Hash function from Chris Torek. */ 167static u_int32_t 168hash4(keyarg, len) 169 const void *keyarg; 170 size_t len; 171{ 172 const u_char *key; 173 size_t loop; 174 u_int32_t h; 175 176#define HASH4a h = (h << 5) - h + *key++; 177#define HASH4b h = (h << 5) + h + *key++; 178#define HASH4 HASH4b 179 180 h = 0; 181 key = keyarg; 182 if (len > 0) { 183 loop = (len + 8 - 1) >> 3; 184 185 switch (len & (8 - 1)) { 186 case 0: 187 do { 188 HASH4; 189 /* FALLTHROUGH */ 190 case 7: 191 HASH4; 192 /* FALLTHROUGH */ 193 case 6: 194 HASH4; 195 /* FALLTHROUGH */ 196 case 5: 197 HASH4; 198 /* FALLTHROUGH */ 199 case 4: 200 HASH4; 201 /* FALLTHROUGH */ 202 case 3: 203 HASH4; 204 /* FALLTHROUGH */ 205 case 2: 206 HASH4; 207 /* FALLTHROUGH */ 208 case 1: 209 HASH4; 210 } while (--loop); 211 } 212 } 213 return (h); 214} 215