stdlib/bsearch.c

   1 /* Copyright (C) 1991, 1992 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.h>
  20 #include <stdlib.h>
  21
  22
  23 /* Perform a binary search for KEY in BASE which has NMEMB elements
  24    of SIZE bytes each.  The comparisons are done by (*COMPAR)().  */
  25 PTR
  26 DEFUN(bsearch, (key, base, nmemb, size, compar),
  27       register CONST PTR key AND register CONST PTR base AND
  28       size_t nmemb AND register size_t size AND
  29       register int EXFUN((*compar), (CONST PTR, CONST PTR)))
  30 {
  31   register size_t l, u, idx;
  32   register CONST PTR p;
  33   register int comparison;
  34
  35   l = 0;
  36   u = nmemb;
  37   while (l < u)
  38     {
  39       idx = (l + u) / 2;
  40       p = (PTR) (((CONST char *) base) + (idx * size));
  41       comparison = (*compar)(key, p);
  42       if (comparison < 0)
  43         u = idx;
  44       else if (comparison > 0)
  45         l = idx + 1;
  46       else
  47         return (PTR) p;
  48     }
  49
  50   return NULL;
  51 }