ec_GFp_nistp521_mod
MP_CHECKOK(ec_GFp_nistp521_mod(r, r, meth));
MP_CHECKOK(ec_GFp_nistp521_mod(r, r, meth));
MP_CHECKOK(ec_GFp_nistp521_mod(r, r, meth));
group->meth->field_mod = &ec_GFp_nistp521_mod;