/* Return a NULL pointer, without letting the compiler know it.

   Copyright (C) 2017-2019 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 3 of the License, or

   (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <stdlib.h>

/* Return NULL.

   Usual compilers are not able to infer something about the return value.  */

static void *

null_ptr (void)

{

  unsigned int x = rand ();

  unsigned int y = x * x;

  if (y & 2)

    return (void *) -1;

  else

    return (void *) 0;

}

/* If you want to know why this always returns NULL, read

   https://en.wikipedia.org/wiki/Quadratic_residue#Prime_power_modulus .  */