code: public static function ROUNDDOWN($number, $digits)
      {
          $number = Functions::flattenSingleValue($number);
          $digits = Functions::flattenSingleValue($digits);
  
          if ((is_numeric($number)) && (is_numeric($digits))) {
              $significance = pow(10, (int) $digits);
              if ($number < 0.0) {
                  return ceil($number * $significance) / $significance;
              }
  
              return floor($number * $significance) / $significance;
          }
  
          return Functions::VALUE();
      }
docs: ROUNDDOWN.
  
  Rounds a number down to a specified number of decimal places
  
  @param float $number Number to round
  @param int $digits Number of digits to which you want to round $number
  
  @return float Rounded Number