UTOPPY_MJD_1970
rv = (mjd < UTOPPY_MJD_1970) ? UTOPPY_MJD_1970 : (uint32_t) mjd;
rv = (rv - UTOPPY_MJD_1970) * 60 * 60 * 24;
utoppy_add_16(sc, mjd + UTOPPY_MJD_1970);