libiberty/bsearch_r.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 [rescinded 22 July 1999]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_r (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 *, void *), void *@var{arg})
  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 three arguments: the first
  42 two point to the @var{key} and to an array member, and the last is passed
  43 down unchanged from @code{bsearch_r}'s last argument.  It should return an
  44 integer less than, equal to, or greater than zero if the @var{key} object
  45 is respectively less than, matching, or greater than the array member.
  46
  47 @end deftypefn
  48
  49 */
  50
  51 #include "config.h"
  52 #include "ansidecl.h"
  53 #include <sys/types.h>          /* size_t */
  54 #include <stdio.h>
  55
  56 /*
  57  * Perform a binary search.
  58  *
  59  * The code below is a bit sneaky.  After a comparison fails, we
  60  * divide the work in half by moving either left or right. If lim
  61  * is odd, moving left simply involves halving lim: e.g., when lim
  62  * is 5 we look at item 2, so we change lim to 2 so that we will
  63  * look at items 0 & 1.  If lim is even, the same applies.  If lim
  64  * is odd, moving right again involes halving lim, this time moving
  65  * the base up one item past p: e.g., when lim is 5 we change base
  66  * to item 3 and make lim 2 so that we will look at items 3 and 4.
  67  * If lim is even, however, we have to shrink it by one before
  68  * halving: e.g., when lim is 4, we still looked at item 2, so we
  69  * have to make lim 3, then halve, obtaining 1, so that we will only
  70  * look at item 3.
  71  */
  72 void *
  73 bsearch_r (const void *key, const void *base0,
  74            size_t nmemb, size_t size,
  75            int (*compar)(const void *, const void *, void *),
  76            void *arg)
  77 {
  78         const char *base = (const char *) base0;
  79         int lim, cmp;
  80         const void *p;
  81
  82         for (lim = nmemb; lim != 0; lim >>= 1) {
  83                 p = base + (lim >> 1) * size;
  84                 cmp = (*compar)(key, p, arg);
  85                 if (cmp == 0)
  86                         return (void *)p;
  87                 if (cmp > 0) {  /* key > p: move right */
  88                         base = (const char *)p + size;
  89                         lim--;
  90                 } /* else move left */
  91         }
  92         return (NULL);
  93 }