code: public static <T extends Number> long divideRoundDown(final T dividend, final T divisor) {
  
          return (long) divide(dividend, divisor);
      }
docs: Returns a long average number by round down with specify dividend and
  divisor.<br>
  Returns 0 if dividend == null or divisor == null.<br>
  Returns 1 if dividend == divisor or divisor == 0.<br>
  e.g: average is 3.5, then return 3.
  
  @param dividend
  number to be handled.
  @param divisor
  number to be handled.
  @return a long average number by given dividend and divisor.