Function to return no of business days between the provided time range

CREATE FUNCTION ufnGetBusinessDays (@DateStart DATETIME, @DateEnd   DATETIME)

RETURNS INT

AS

  BEGIN

    IF (@DateStart IS NULL OR @DateEnd IS NULL)  RETURN (0)

    DECLARE  @i INT = 0; 

    WHILE (@DateStart <= @DateEnd)

      BEGIN

        SET @i = @i + CASE

                        WHEN datepart(dw,@DateStart) BETWEEN 2 AND 6 THEN 1

                        ELSE 0

                      END 

        SET @DateStart = @DateStart + 1

      END  -- while 

    RETURN (@i)

  END -- function

GO

SELECT dbo.ufnGetBusinessDays('2016-01-01','2016-12-31')