fnul.c

this is a gcc file, you can download it and learn its usetility, for further detail please look at t

main ()
{
  int i;
  int f;

  for (i = 0;; i--)
    {
      f = 0;

      if ((i & (i - 1)) == 0)
	{
	  printf ("d");
	  f = 1;
	}
      if ((i & -i) == i)
	{
	  printf ("t");
	  f = 1;
	}
      if (f)
	printf ("%d\n", i);
    }
}