code: long yearsUntil(InternationalFixedDate end) {
          long startYear = this.prolepticYear * 512L + this.getInternalDayOfYear();
          long endYear = end.prolepticYear * 512L + end.getInternalDayOfYear();
          return (endYear - startYear) / 512L;
      }
docs: Get the number of years from this date to the given day.
  
  @param end The end date.
  @return The number of years from this date to the given day.