h_func.c (5923B)
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. ***REMOVED*** - see 17 * ftp://ftp.cs.berkeley.edu/pub/4bsd/README.Impt.License.Change 18 * 4. 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 39 #ifndef macintosh 40 #include <sys/types.h> 41 #endif 42 #include "mcom_db.h" 43 #include "hash.h" 44 #include "page.h" 45 /* #include "extern.h" */ 46 47 #if 0 48 static uint32 hash1(const void *, size_t); 49 static uint32 hash2(const void *, size_t); 50 static uint32 hash3(const void *, size_t); 51 #endif 52 static uint32 hash4(const void *, size_t); 53 54 /* Global default hash function */ 55 uint32 (*dbm_default_hash)(const void *, size_t) = hash4; 56 57 /* 58 * HASH FUNCTIONS 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 * This came from ejb's hsearch. 64 */ 65 66 #define PRIME1 37 67 #define PRIME2 1048583 68 69 #if 0 70 static uint32 71 hash1(const void *keyarg, register size_t len) 72 { 73 register const uint8 *key; 74 register uint32 h; 75 76 /* Convert string to integer */ 77 for (key = (const uint8 *)keyarg, h = 0; len--;) 78 h = h * PRIME1 ^ (*key++ - ' '); 79 h %= PRIME2; 80 return (h); 81 } 82 83 /* 84 * Phong's linear congruential hash 85 */ 86 #define dcharhash(h, c) ((h) = 0x63c63cd9 * (h) + 0x9c39c33d + (c)) 87 88 static uint32 89 hash2(const void *keyarg, size_t len) 90 { 91 register const uint8 *e, *key; 92 register uint32 h; 93 register uint8 c; 94 95 key = (const uint8 *)keyarg; 96 e = key + len; 97 for (h = 0; key != e;) { 98 c = *key++; 99 if (!c && key > e) 100 break; 101 dcharhash(h, c); 102 } 103 return (h); 104 } 105 106 /* 107 * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte 108 * units. On the first time through the loop we get the "leftover bytes" 109 * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle 110 * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If 111 * this routine is heavily used enough, it's worth the ugly coding. 112 * 113 * OZ's original sdbm hash 114 */ 115 static uint32 116 hash3(const void *keyarg, register size_t len) 117 { 118 register const uint8 *key; 119 register size_t loop; 120 register uint32 h; 121 122 #define HASHC h = *key++ + 65599 * h 123 124 h = 0; 125 key = (const uint8 *)keyarg; 126 if (len > 0) { 127 loop = (len + 8 - 1) >> 3; 128 129 switch (len & (8 - 1)) { 130 case 0: 131 do { 132 HASHC; 133 /* FALLTHROUGH */ 134 case 7: 135 HASHC; 136 /* FALLTHROUGH */ 137 case 6: 138 HASHC; 139 /* FALLTHROUGH */ 140 case 5: 141 HASHC; 142 /* FALLTHROUGH */ 143 case 4: 144 HASHC; 145 /* FALLTHROUGH */ 146 case 3: 147 HASHC; 148 /* FALLTHROUGH */ 149 case 2: 150 HASHC; 151 /* FALLTHROUGH */ 152 case 1: 153 HASHC; 154 } while (--loop); 155 } 156 } 157 return (h); 158 } 159 #endif /* 0 */ 160 161 /* Hash function from Chris Torek. */ 162 static uint32 163 hash4(const void *keyarg, register size_t len) 164 { 165 register const uint8 *key; 166 register size_t loop; 167 register uint32 h; 168 169 #define HASH4a h = (h << 5) - h + *key++; 170 #define HASH4b h = (h << 5) + h + *key++; 171 #define HASH4 HASH4b 172 173 h = 0; 174 key = (const uint8 *)keyarg; 175 if (len > 0) { 176 loop = (len + 8 - 1) >> 3; 177 178 switch (len & (8 - 1)) { 179 case 0: 180 do { 181 HASH4; 182 /* FALLTHROUGH */ 183 case 7: 184 HASH4; 185 /* FALLTHROUGH */ 186 case 6: 187 HASH4; 188 /* FALLTHROUGH */ 189 case 5: 190 HASH4; 191 /* FALLTHROUGH */ 192 case 4: 193 HASH4; 194 /* FALLTHROUGH */ 195 case 3: 196 HASH4; 197 /* FALLTHROUGH */ 198 case 2: 199 HASH4; 200 /* FALLTHROUGH */ 201 case 1: 202 HASH4; 203 } while (--loop); 204 } 205 } 206 return (h); 207 }