tests/null-ptr.h

   1 /* Return a NULL pointer, without letting the compiler know it.
   2    Copyright (C) 2017-2024 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation, either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program 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
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 #include <stdlib.h>
  18
  19 /* Return NULL.
  20    Usual compilers are not able to infer something about the return value.  */
  21 static void *
  22 null_ptr (void)
  23 {
  24   unsigned int x = rand ();
  25   unsigned int y = x * x;
  26   if (y & 2)
  27     return (void *) -1;
  28   else
  29     return (void *) 0;
  30 }
  31
  32 /* If you want to know why this always returns NULL, read
  33    https://en.wikipedia.org/wiki/Quadratic_residue#Prime_power_modulus .  */