code: public static int ceToJD(long year, int month, int day, int jdEpochOffset) {
  
          // Julian<->Ethiopic algorithms from:
          // "Calendars in Ethiopia", Berhanu Beyene, Manfred Kudlek, International Conference
          // of Ethiopian Studies XV, Hamburg, 2003
  
          // handle month > 12, < 0 (e.g. from add/set)
          if ( month >= 0 ) {
              year += month/13;
              month %= 13;
          } else {
              ++month;
              year += month/13 - 1;
              month = month%13 + 12;
          }
          return (int) (
              jdEpochOffset           // difference from Julian epoch to 1,1,1
              + 365 * year            // number of days from years
              + floorDivide(year, 4)  // extra day of leap year
              + 30 * month            // number of days from months (months are 0-based)
              + day - 1               // number of days for present month (1 based)
              );
      }
docs: Convert an Coptic/Ethiopic year, month and day to a Julian day
  @param year the extended year
  @param month the month
  @param day the day
  @return Julian day
  @hide unsupported on Android