libiberty/bsearch.c

   1 /*
   2  * Copyright (c) 1990 Regents of the University of California.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. [rescinded 22 July 1999]
  14  * 4. Neither the name of the University nor the names of its contributors
  15  *    may be used to endorse or promote products derived from this software
  16  *    without specific prior written permission.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  20  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  21  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  22  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  23  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  24  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  25  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  28  * SUCH DAMAGE.
  29  */
  30
  31 #include "config.h"
  32 #include "ansidecl.h"
  33 #include <sys/types.h>          /* size_t */
  34 #include <stdio.h>
  35
  36 /*
  37  * Perform a binary search.
  38  *
  39  * The code below is a bit sneaky.  After a comparison fails, we
  40  * divide the work in half by moving either left or right. If lim
  41  * is odd, moving left simply involves halving lim: e.g., when lim
  42  * is 5 we look at item 2, so we change lim to 2 so that we will
  43  * look at items 0 & 1.  If lim is even, the same applies.  If lim
  44  * is odd, moving right again involes halving lim, this time moving
  45  * the base up one item past p: e.g., when lim is 5 we change base
  46  * to item 3 and make lim 2 so that we will look at items 3 and 4.
  47  * If lim is even, however, we have to shrink it by one before
  48  * halving: e.g., when lim is 4, we still looked at item 2, so we
  49  * have to make lim 3, then halve, obtaining 1, so that we will only
  50  * look at item 3.
  51  */
  52 void *
  53 bsearch(key, base0, nmemb, size, compar)
  54         register void *key;
  55         void *base0;
  56         size_t nmemb;
  57         register size_t size;
  58         register int (*compar)();
  59 {
  60         register char *base = base0;
  61         register int lim, cmp;
  62         register void *p;
  63
  64         for (lim = nmemb; lim != 0; lim >>= 1) {
  65                 p = base + (lim >> 1) * size;
  66                 cmp = (*compar)(key, p);
  67                 if (cmp == 0)
  68                         return (p);
  69                 if (cmp > 0) {  /* key > p: move right */
  70                         base = (char *)p + size;
  71                         lim--;
  72                 } /* else move left */
  73         }
  74         return (NULL);
  75 }