LIBZIB_OBJ*	T_LIBZIB_OBJ

INPUT
T_LIBZIB_OBJ
	if (SvROK($arg) && sv_derived_from($arg, CLASSNAME)) {
	    $var = (LIBZIB_OBJ*)SvRV($arg);
	}
	else
	    croak(\"$var is not derived from \"CLASSNAME\"\")