20020413-1.c

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

void test(long double val, int *eval)
{
  long double tmp = 1.0l;
  int i = 0;

  if (val < 0.0l)
    val = -val;

  if (val >= tmp)
    while (tmp < val)
      {
	tmp *= 2.0l;
	if (i++ >= 10)
	  abort ();
      }
  else if (val != 0.0l)
    while (val < tmp)
      {
	tmp /= 2.0l;
	if (i++ >= 10)
	  abort ();
      }

  *eval = i;
}

int main(void)
{
  int eval;

  test(3.0, &eval);
  test(3.5, &eval);
  test(4.0, &eval);
  test(5.0, &eval);
  exit (0);
}