glibc/bits/stdlib-bsearch.h

/* Perform binary search - inline version.
   Copyright (C) 1991-2017 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

__extern_inline void *
bsearch (const void *__key, const void *__base, size_t __nmemb, size_t __size,
	 __compar_fn_t __compar)
{
  size_t __l, __u, __idx;
  const void *__p;
  int __comparison;

  __l = 0;
  __u = __nmemb;
  while (__l < __u)
    {
      __idx = (__l + __u) / 2;
      __p = (void *) (((const char *) __base) + (__idx * __size));
      __comparison = (*__compar) (__key, __p);
      if (__comparison < 0)
	__u = __idx;
      else if (__comparison > 0)
	__l = __idx + 1;
      else
	return (void *) __p;
    }

  return NULL;
}