public static function Ut1tai($ut11, $ut12, $dta, &$tai1, &$tai2) {
    $dtad;

    /* Result, safeguarding precision. */
    $dtad = $dta / DAYSEC;
    if ($ut11 > $ut12) {
      $tai1 = $ut11;
      $tai2 = $ut12 - $dtad;
    }
    else {
      $tai1 = $ut11 - $dtad;
      $tai2 = $ut12;
    }

    /* Status (always OK). */
    return 0;
  }