1 /* Return a NULL pointer, without letting the compiler know it.
2 Copyright (C) 2017-2021 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 *
null_ptr(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 . */
34