lib/libc/db/hash/hfunc.c

   1 /*-
   2  * Copyright (c) 1990 The Regents of the University of California.
   3  * 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[] = "@(#)hfunc.c     5.1 (Berkeley) 2/12/91";
  39 #endif /* LIBC_SCCS and not lint */
  40
  41 /* Global default hash function */
  42 static  int     hash1();
  43 static  int     hash2();
  44 static  int     hash3();
  45 static  int     hash4();
  46
  47 int     (*default_hash)() = hash4;
  48
  49 /******************************* HASH FUNCTIONS **************************/
  50 /*
  51         Assume that we've already split the bucket to which this
  52         key hashes, calculate that bucket, and check that in fact
  53         we did already split it.
  54
  55         This came from ejb's hsearch.
  56 */
  57
  58 # define PRIME1                 37
  59 # define PRIME2                 1048583
  60
  61 static int
  62 hash1(key,len)
  63 char *key;
  64 int len;
  65 {
  66         register int h;
  67         register int l = len;
  68         register unsigned char *k = (unsigned char *) key;
  69
  70         h = 0;
  71         /*
  72          * Convert string to integer
  73          */
  74         while (l--) h = h * PRIME1 ^ (*k++ - ' ');
  75         h %= PRIME2;
  76
  77         return (h);
  78 }
  79
  80 /*
  81     Phong's linear congruential hash
  82 */
  83 #define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
  84
  85 static int
  86 hash2(str, n)
  87         register unsigned char *str;
  88         int n;
  89 {
  90         register unsigned char *e, c;
  91         register int h;
  92
  93         e = str + n;
  94         for (h = 0; str != e;) {
  95                 c = *str++;
  96                 if (!c && str > e)
  97                         break;
  98                 dcharhash(h,c);
  99         }
 100         return(h);
 101 }
 102
 103 /*
 104  * This is INCREDIBLY ugly, but fast.
 105  * We break the string up into 8 byte units.  On the first time
 106  * through the loop we get the "leftover bytes" (strlen % 8).
 107  * On every other iteration, we perform 8 HASHC's so we handle
 108  * all 8 bytes.  Essentially, this saves us 7 cmp & branch
 109  * instructions.  If this routine is heavily used enough, it's
 110  * worth the ugly coding
 111  *
 112  * OZ's original sdbm hash
 113  */
 114 static int
 115 hash3(key,nbytes)
 116 char *key;
 117 int nbytes;
 118 {
 119         register int n = 0;
 120         register char *str = key;
 121         register int loop;
 122         register int len = nbytes;
 123
 124 #define HASHC   n = *str++ + 65599 * n
 125
 126         if (len > 0) {
 127                 loop = (len + 8 - 1) >> 3;
 128
 129                 switch(len & (8 - 1)) {
 130                         case 0: do {            /* All fall throughs */
 131                                         HASHC;
 132                                 case 7: HASHC;
 133                                 case 6: HASHC;
 134                                 case 5: HASHC;
 135                                 case 4: HASHC;
 136                                 case 3: HASHC;
 137                                 case 2: HASHC;
 138                                 case 1: HASHC;
 139                         } while (--loop);
 140                 }
 141
 142         }
 143         return(n);
 144 }
 145
 146 /* Hash function from Chris Torek */
 147 static int
 148 hash4(key,nbytes)
 149 char    *key;
 150 int     nbytes;
 151 {
 152         register int h = 0;
 153         register char *p = key;
 154         register int loop;
 155         register int len = nbytes;
 156
 157 #define HASH4a   h = (h << 5) - h + *p++;
 158 #define HASH4b   h = (h << 5) + h + *p++;
 159 #define HASH4 HASH4b
 160
 161         if (len > 0) {
 162                 loop = (len + 8 - 1) >> 3;
 163
 164                 switch(len & (8 - 1)) {
 165                         case 0: do {            /* All fall throughs */
 166                                         HASH4;
 167                                 case 7: HASH4;
 168                                 case 6: HASH4;
 169                                 case 5: HASH4;
 170                                 case 4: HASH4;
 171                                 case 3: HASH4;
 172                                 case 2: HASH4;
 173                                 case 1: HASH4;
 174                         } while (--loop);
 175                 }
 176
 177         }
 178         return(h);
 179 }