1  extern int __fpclassifyd (double x);
       2  
       3  double fdim (double x, double y)
       4  {
       5     int c = __fpclassifyd (x);
       6     if (c == 0)
       7       return (x);
       8     if (__fpclassifyd (y) == 0)
       9       return (y);
      10     if (c == 1)
      11       return (__builtin_huge_val ());
      12     return x > y ? x - y : 0.0;
      13  }