db/hash/FreeBSD/hash_func.c

   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  * 4. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 #if defined(LIBC_SCCS) && !defined(lint)
  34 static char sccsid[] = "@(#)hash_func.c 8.2 (Berkeley) 2/21/94";
  35 #endif /* LIBC_SCCS and not lint */
  36 #include <sys/cdefs.h>
  37 __FBSDID("$FreeBSD: src/lib/libc/db/hash/hash_func.c,v 1.6 2007/01/09 00:27:50 imp Exp $");
  38
  39 #include <sys/types.h>
  40
  41 #include <db.h>
  42 #include "hash.h"
  43 #include "page.h"
  44 #include "extern.h"
  45
  46 static u_int32_t hash1(const void *, size_t) __unused;
  47 static u_int32_t hash2(const void *, size_t) __unused;
  48 static u_int32_t hash3(const void *, size_t) __unused;
  49 static u_int32_t hash4(const void *, size_t);
  50
  51 /* Global default hash function */
  52 u_int32_t (*__default_hash)(const void *, size_t) = hash4;
  53
  54 /*
  55  * HASH FUNCTIONS
  56  *
  57  * Assume that we've already split the bucket to which this key hashes,
  58  * calculate that bucket, and check that in fact we did already split it.
  59  *
  60  * This came from ejb's hsearch.
  61  */
  62
  63 #define PRIME1          37
  64 #define PRIME2          1048583
  65
  66 static u_int32_t
  67 hash1(keyarg, len)
  68         const void *keyarg;
  69         size_t len;
  70 {
  71         const u_char *key;
  72         u_int32_t h;
  73
  74         /* Convert string to integer */
  75         for (key = keyarg, h = 0; len--;)
  76                 h = h * PRIME1 ^ (*key++ - ' ');
  77         h %= PRIME2;
  78         return (h);
  79 }
  80
  81 /*
  82  * Phong's linear congruential hash
  83  */
  84 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
  85
  86 static u_int32_t
  87 hash2(keyarg, len)
  88         const void *keyarg;
  89         size_t len;
  90 {
  91         const u_char *e, *key;
  92         u_int32_t h;
  93         u_char c;
  94
  95         key = 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 u_int32_t
 116 hash3(keyarg, len)
 117         const void *keyarg;
 118         size_t len;
 119 {
 120         const u_char *key;
 121         size_t loop;
 122         u_int32_t h;
 123
 124 #define HASHC   h = *key++ + 65599 * h
 125
 126         h = 0;
 127         key = keyarg;
 128         if (len > 0) {
 129                 loop = (len + 8 - 1) >> 3;
 130
 131                 switch (len & (8 - 1)) {
 132                 case 0:
 133                         do {
 134                                 HASHC;
 135                                 /* FALLTHROUGH */
 136                 case 7:
 137                                 HASHC;
 138                                 /* FALLTHROUGH */
 139                 case 6:
 140                                 HASHC;
 141                                 /* FALLTHROUGH */
 142                 case 5:
 143                                 HASHC;
 144                                 /* FALLTHROUGH */
 145                 case 4:
 146                                 HASHC;
 147                                 /* FALLTHROUGH */
 148                 case 3:
 149                                 HASHC;
 150                                 /* FALLTHROUGH */
 151                 case 2:
 152                                 HASHC;
 153                                 /* FALLTHROUGH */
 154                 case 1:
 155                                 HASHC;
 156                         } while (--loop);
 157                 }
 158         }
 159         return (h);
 160 }
 161
 162 /* Hash function from Chris Torek. */
 163 static u_int32_t
 164 hash4(keyarg, len)
 165         const void *keyarg;
 166         size_t len;
 167 {
 168         const u_char *key;
 169         size_t loop;
 170         u_int32_t h;
 171
 172 #define HASH4a   h = (h << 5) - h + *key++;
 173 #define HASH4b   h = (h << 5) + h + *key++;
 174 #define HASH4 HASH4b
 175
 176         h = 0;
 177         key = keyarg;
 178         if (len > 0) {
 179                 loop = (len + 8 - 1) >> 3;
 180
 181                 switch (len & (8 - 1)) {
 182                 case 0:
 183                         do {
 184                                 HASH4;
 185                                 /* FALLTHROUGH */
 186                 case 7:
 187                                 HASH4;
 188                                 /* FALLTHROUGH */
 189                 case 6:
 190                                 HASH4;
 191                                 /* FALLTHROUGH */
 192                 case 5:
 193                                 HASH4;
 194                                 /* FALLTHROUGH */
 195                 case 4:
 196                                 HASH4;
 197                                 /* FALLTHROUGH */
 198                 case 3:
 199                                 HASH4;
 200                                 /* FALLTHROUGH */
 201                 case 2:
 202                                 HASH4;
 203                                 /* FALLTHROUGH */
 204                 case 1:
 205                                 HASH4;
 206                         } while (--loop);
 207                 }
 208         }
 209         return (h);
 210 }