Subversion Repositories Kolibri OS

Rev

Go to most recent revision | Blame | Last modification | View Log | Download | RSS feed

  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. ANSI_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. TRAD_SYNOPSIS
  30.         #include <stdlib.h>
  31.         char *bsearch(<[key]>, <[base]>, <[nmemb]>, <[size]>, <[compar]>)
  32.         char *<[key]>;
  33.         char *<[base]>;
  34.         size_t <[nmemb]>, <[size]>;
  35.         int (*<[compar]>)();
  36.  
  37. DESCRIPTION
  38. <<bsearch>> searches an array beginning at <[base]> for any element
  39. that matches <[key]>, using binary search.  <[nmemb]> is the element
  40. count of the array; <[size]> is the size of each element.
  41.  
  42. The array must be sorted in ascending order with respect to the
  43. comparison function <[compar]> (which you supply as the last argument of
  44. <<bsearch>>).
  45.  
  46. You must define the comparison function <<(*<[compar]>)>> to have two
  47. arguments; its result must be negative if the first argument is
  48. less than the second, zero if the two arguments match, and
  49. positive if the first argument is greater than the second (where
  50. ``less than'' and ``greater than'' refer to whatever arbitrary
  51. ordering is appropriate).
  52.  
  53. RETURNS
  54. Returns a pointer to an element of <[array]> that matches <[key]>.  If
  55. more than one matching element is available, the result may point to
  56. any of them.
  57.  
  58. PORTABILITY
  59. <<bsearch>> is ANSI.
  60.  
  61. No supporting OS subroutines are required.
  62. */
  63.  
  64. #include <_ansi.h>
  65. #include <reent.h>
  66. #include <stdlib.h>
  67.  
  68. _PTR
  69. _DEFUN (bsearch, (key, base, nmemb, size, compar),
  70.         _CONST _PTR key _AND
  71.         _CONST _PTR base _AND
  72.         size_t nmemb _AND
  73.         size_t size _AND
  74.         int _EXFNPTR(compar, (const _PTR, const _PTR)))
  75. {
  76.   _PTR current;
  77.   size_t lower = 0;
  78.   size_t upper = nmemb;
  79.   size_t index;
  80.   int result;
  81.  
  82.   if (nmemb == 0 || size == 0)
  83.     return NULL;
  84.  
  85.   while (lower < upper)
  86.     {
  87.       index = (lower + upper) / 2;
  88.       current = (_PTR) (((char *) base) + (index * size));
  89.  
  90.       result = compar (key, current);
  91.  
  92.       if (result < 0)
  93.         upper = index;
  94.       else if (result > 0)
  95.         lower = index + 1;
  96.       else
  97.         return current;
  98.     }
  99.  
  100.   return NULL;
  101. }
  102.  
  103.