public static function Utcut1($utc1, $utc2, $dut1, &$ut11, &$ut12) {
    $iy;
    $im;
    $id;
    $js;
    $jw;
    $w;
    $dat;
    $dta;
    $tai1;
    $tai2;

    /* Look up TAI-UTC. */
    if (IAU::Jd2cal($utc1, $utc2, $iy, $im, $id, $w))
      return -1;
    $js = IAU::Dat($iy, $im, $id, 0.0, $dat);
    if ($js < 0)
      return -1;

    /* Form UT1-TAI. */
    $dta = $dut1 - $dat;

    /* UTC to TAI to UT1. */
    $jw = IAU::Utctai($utc1, $utc2, $tai1, $tai2);
    if ($jw < 0) {
      return -1;
    }
    else if ($jw > 0) {
      $js = $jw;
    }
    if (IAU::Taiut1($tai1, $tai2, $dta, $ut11, $ut12))
      return -1;

    /* Status. */
    return $js;
  }