TYPEMAP
BIGNUM*      T_PTR
rsaData*     O_OBJECT

INPUT
O_OBJECT
    if (!(SvROK($arg) && sv_derived_from($arg, PACKAGE_NAME)))
    {
        croak(\"argument is not a ${type} object\");
    }
    $var = (${type}) SvIV(SvRV($arg));

OUTPUT