newlib/libc/search/bsearch.c

   1 /*
   2  * bsearch.c
   3  * Original Author:     G. Haley
   4  * Rewritten by:        G. Noer
   5  *
   6  * Searches an array of nmemb members, the initial member of which is pointed
   7  * to by base, for a member that matches the object pointed to by key. The
   8  * contents of the array shall be in ascending order according to a comparison
   9  * function pointed to by compar. The function shall return an integer less
  10  * than, equal to or greater than zero if the first argument is considered to be
  11  * respectively less than, equal to or greater than the second. Returns a
  12  * pointer to the matching member of the array, or a null pointer if no match
  13  * is found.
  14  */
  15
  16 /*
  17 FUNCTION
  18 <<bsearch>>---binary search
  19
  20 INDEX
  21         bsearch
  22
  23 SYNOPSIS
  24         #include <stdlib.h>
  25         void *bsearch(const void *<[key]>, const void *<[base]>,
  26                 size_t <[nmemb]>, size_t <[size]>,
  27                 int (*<[compar]>)(const void *, const void *));
  28
  29 DESCRIPTION
  30 <<bsearch>> searches an array beginning at <[base]> for any element
  31 that matches <[key]>, using binary search.  <[nmemb]> is the element
  32 count of the array; <[size]> is the size of each element.
  33
  34 The array must be sorted in ascending order with respect to the
  35 comparison function <[compar]> (which you supply as the last argument of
  36 <<bsearch>>).
  37
  38 You must define the comparison function <<(*<[compar]>)>> to have two
  39 arguments; its result must be negative if the first argument is
  40 less than the second, zero if the two arguments match, and
  41 positive if the first argument is greater than the second (where
  42 ``less than'' and ``greater than'' refer to whatever arbitrary
  43 ordering is appropriate).
  44
  45 RETURNS
  46 Returns a pointer to an element of <[array]> that matches <[key]>.  If
  47 more than one matching element is available, the result may point to
  48 any of them.
  49
  50 PORTABILITY
  51 <<bsearch>> is ANSI.
  52
  53 No supporting OS subroutines are required.
  54 */
  55
  56 #include <stdlib.h>
  57
  58 void *
  59 bsearch (const void *key,
  60         const void *base,
  61         size_t nmemb,
  62         size_t size,
  63         int (*compar) (const void *, const void *))
  64 {
  65   void *current;
  66   size_t lower = 0;
  67   size_t upper = nmemb;
  68   size_t index;
  69   int result;
  70
  71   if (nmemb == 0 || size == 0)
  72     return NULL;
  73
  74   while (lower < upper)
  75     {
  76       index = (lower + upper) / 2;
  77       current = (void *) (((char *) base) + (index * size));
  78
  79       result = compar (key, current);
  80
  81       if (result < 0)
  82         upper = index;
  83       else if (result > 0)
  84         lower = index + 1;
  85       else
  86         return current;
  87     }
  88
  89   return NULL;
  90 }
  91