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 [rescinded 22 July 1999]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 /*
  32
  33 @deftypefn Supplemental void* bsearch (const void *@var{key}, @
  34   const void *@var{base}, size_t @var{nmemb}, size_t @var{size}, @
  35   int (*@var{compar})(const void *, const void *))
  36
  37 Performs a search over an array of @var{nmemb} elements pointed to by
  38 @var{base} for a member that matches the object pointed to by @var{key}.
  39 The size of each member is specified by @var{size}.  The array contents
  40 should be sorted in ascending order according to the @var{compar}
  41 comparison function.  This routine should take two arguments pointing to
  42 the @var{key} and to an array member, in that order, and should return an
  43 integer less than, equal to, or greater than zero if the @var{key} object
  44 is respectively less than, matching, or greater than the array member.
  45
  46 @end deftypefn
  47
  48 */
  49
  50 #include "config.h"
  51 #include "ansidecl.h"
  52 #include <sys/types.h>          /* size_t */
  53 #include <stdio.h>
  54
  55 /*
  56  * Perform a binary search.
  57  *
  58  * The code below is a bit sneaky.  After a comparison fails, we
  59  * divide the work in half by moving either left or right. If lim
  60  * is odd, moving left simply involves halving lim: e.g., when lim
  61  * is 5 we look at item 2, so we change lim to 2 so that we will
  62  * look at items 0 & 1.  If lim is even, the same applies.  If lim
  63  * is odd, moving right again involes halving lim, this time moving
  64  * the base up one item past p: e.g., when lim is 5 we change base
  65  * to item 3 and make lim 2 so that we will look at items 3 and 4.
  66  * If lim is even, however, we have to shrink it by one before
  67  * halving: e.g., when lim is 4, we still looked at item 2, so we
  68  * have to make lim 3, then halve, obtaining 1, so that we will only
  69  * look at item 3.
  70  */
  71 void *
  72 bsearch (register const void *key, const void *base0,
  73          size_t nmemb, register size_t size,
  74          register int (*compar)(const void *, const void *))
  75 {
  76         register const char *base = (const char *) base0;
  77         register int lim, cmp;
  78         register const void *p;
  79
  80         for (lim = nmemb; lim != 0; lim >>= 1) {
  81                 p = base + (lim >> 1) * size;
  82                 cmp = (*compar)(key, p);
  83                 if (cmp == 0)
  84                         return (void *)p;
  85                 if (cmp > 0) {  /* key > p: move right */
  86                         base = (const char *)p + size;
  87                         lim--;
  88                 } /* else move left */
  89         }
  90         return (NULL);
  91 }