1 /*- 2 * See the file LICENSE for redistribution information. 3 * 4 * Copyright (c) 1996, 1997 5 * Sleepycat Software. All rights reserved. 6 */ 7 /* 8 * Copyright (c) 1990, 1993 9 * Margo Seltzer. All rights reserved. 10 */ 11 /* 12 * Copyright (c) 1990, 1993 13 * The Regents of the University of California. All rights reserved. 14 * 15 * This code is derived from software contributed to Berkeley by 16 * Margo Seltzer. 17 * 18 * Redistribution and use in source and binary forms, with or without 19 * modification, are permitted provided that the following conditions 20 * are met: 21 * 1. Redistributions of source code must retain the above copyright 22 * notice, this list of conditions and the following disclaimer. 23 * 2. Redistributions in binary form must reproduce the above copyright 24 * notice, this list of conditions and the following disclaimer in the 25 * documentation and/or other materials provided with the distribution. 26 * 3. All advertising materials mentioning features or use of this software 27 * must display the following acknowledgement: 28 * This product includes software developed by the University of 29 * California, Berkeley and its contributors. 30 * 4. Neither the name of the University nor the names of its contributors 31 * may be used to endorse or promote products derived from this software 32 * without specific prior written permission. 33 * 34 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 35 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 36 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 37 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 38 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 39 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 40 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 41 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 42 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 43 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 44 * SUCH DAMAGE. 45 */ 46 /* 47 * Copyright (c) 1998 by Sun Microsystems, Inc. 48 * All rights reserved. 49 */ 50 51 #include "config.h" 52 53 #pragma ident "%Z%%M% %I% %E% SMI" 54 55 #ifndef lint 56 static const char sccsid[] = "@(#)hash_func.c 10.7 (Sleepycat) 9/16/97"; 57 static const char sccsi2[] = "%W% (Sun) %G%"; 58 #endif /* not lint */ 59 60 #ifndef NO_SYSTEM_INCLUDES 61 #include <sys/types.h> 62 #endif 63 64 #include "db_int.h" 65 #include "db_page.h" 66 #include "hash.h" 67 68 /* 69 * __ham_func2 -- 70 * Phong Vo's linear congruential hash. 71 * 72 * PUBLIC: u_int32_t __ham_func2 __P((const void *, u_int32_t)); 73 */ 74 #define DCHARHASH(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c)) 75 76 u_int32_t 77 __ham_func2(key, len) 78 const void *key; 79 u_int32_t len; 80 { 81 const u_int8_t *e, *k; 82 u_int32_t h; 83 u_int8_t c; 84 85 k = key; 86 e = k + len; 87 for (h = 0; k != e;) { 88 c = *k++; 89 if (!c && k > e) 90 break; 91 DCHARHASH(h, c); 92 } 93 return (h); 94 } 95 96 /* 97 * __ham_func3 -- 98 * Ozan Yigit's original sdbm hash. 99 * 100 * Ugly, but fast. Break the string up into 8 byte units. On the first time 101 * through the loop get the "leftover bytes" (strlen % 8). On every other 102 * iteration, perform 8 HASHC's so we handle all 8 bytes. Essentially, this 103 * saves us 7 cmp & branch instructions. 104 * 105 * PUBLIC: u_int32_t __ham_func3 __P((const void *, u_int32_t)); 106 */ 107 u_int32_t 108 __ham_func3(key, len) 109 const void *key; 110 u_int32_t len; 111 { 112 const u_int8_t *k; 113 u_int32_t n, loop; 114 115 if (len == 0) 116 return (0); 117 118 #define HASHC n = *k++ + 65599 * n 119 n = 0; 120 k = key; 121 122 loop = (len + 8 - 1) >> 3; 123 switch (len & (8 - 1)) { 124 case 0: 125 do { 126 HASHC; 127 case 7: 128 HASHC; 129 case 6: 130 HASHC; 131 case 5: 132 HASHC; 133 case 4: 134 HASHC; 135 case 3: 136 HASHC; 137 case 2: 138 HASHC; 139 case 1: 140 HASHC; 141 } while (--loop); 142 } 143 return (n); 144 } 145 146 /* 147 * __ham_func4 -- 148 * Chris Torek's hash function. Although this function performs only 149 * slightly worse than __ham_func5 on strings, it performs horribly on 150 * numbers. 151 * 152 * PUBLIC: u_int32_t __ham_func4 __P((const void *, u_int32_t)); 153 */ 154 u_int32_t 155 __ham_func4(key, len) 156 const void *key; 157 u_int32_t len; 158 { 159 const u_int8_t *k; 160 u_int32_t h, loop; 161 162 if (len == 0) 163 return (0); 164 165 #define HASH4a h = (h << 5) - h + *k++; 166 #define HASH4b h = (h << 5) + h + *k++; 167 #define HASH4 HASH4b 168 h = 0; 169 k = key; 170 171 loop = (len + 8 - 1) >> 3; 172 switch (len & (8 - 1)) { 173 case 0: 174 do { 175 HASH4; 176 case 7: 177 HASH4; 178 case 6: 179 HASH4; 180 case 5: 181 HASH4; 182 case 4: 183 HASH4; 184 case 3: 185 HASH4; 186 case 2: 187 HASH4; 188 case 1: 189 HASH4; 190 } while (--loop); 191 } 192 return (h); 193 } 194 195 /* 196 * Fowler/Noll/Vo hash 197 * 198 * The basis of the hash algorithm was taken from an idea sent by email to the 199 * IEEE Posix P1003.2 mailing list from Phong Vo (kpv@research.att.com) and 200 * Glenn Fowler (gsf@research.att.com). Landon Curt Noll (chongo@toad.com) 201 * later improved on their algorithm. 202 * 203 * The magic is in the interesting relationship between the special prime 204 * 16777619 (2^24 + 403) and 2^32 and 2^8. 205 * 206 * This hash produces the fewest collisions of any function that we've seen so 207 * far, and works well on both numbers and strings. 208 * 209 * PUBLIC: u_int32_t __ham_func5 __P((const void *, u_int32_t)); 210 */ 211 u_int32_t 212 __ham_func5(key, len) 213 const void *key; 214 u_int32_t len; 215 { 216 const u_int8_t *k, *e; 217 u_int32_t h; 218 219 k = key; 220 e = k + len; 221 for (h = 0; k < e; ++k) { 222 h *= 16777619; 223 h ^= *k; 224 } 225 return (h); 226 } 227