code: public static CalendarDays between(
          CalendarDate start,
          CalendarDate end
      ){
  
          long t1 = start.getDaysSinceEpochUTC();
          long t2 = end.getDaysSinceEpochUTC();
          return CalendarDays.of(Math.subtractExact(t2, t1));
  
      }
docs: /*[deutsch]
  <p>Berechnet die Tagesdifferenz zwischen den angegebenen Datumsobjekten. </p>
  
  @param   start   first calendar date (inclusive)
  @param   end     second calendar date (exclusive)
  @return  count of calendar days between start and end
  @since   3.8/4.5