960405-1.c

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

#define X  5.9486574767861588254287966331400356538172e4931L

long double x = X + X;
long double y = 2.0L * X;

main ()
{
#if ! defined (__vax__) && ! defined (_CRAY)
  if (x != y)
    abort ();
#endif
  exit (0);
}