SQL Server - Get Last Day of a given Month

This function will return the last day of a given month based upon the date passed in. 


-------------------------------------------------
--Create Function to return the last day of the
--week based upon the date passed in.
--
--You pass in a Date and it return
--the Date for last day of the week
-------------------------------------------------
CREATE FUNCTION [dbo].[xGetLastDayOfMonth](@Date DateTime)
RETURNS DateTime
AS

BEGIN

    DECLARE @DayOfMonth        INT
    DECLARE @AddOneMonthToDate DateTime

    -- Add one month to the date passed in
    SET @AddOneMonthToDate = DateAdd(m,1,@Date)

    -- Get the day number of @AddOneMonthToDate
        -- When adding one Month to the passed in Date
        -- we could end up with a different day than
        -- the original month.  Add one month to 1/31/2011
        -- and we get 2/28/2011.  We want to make sure
        -- we get day number in the next month.
    SET @DayOfMonth = DAY(@AddOneMonthToDate)



    -- We will now subtract the @DayOfMonth
    -- from the @AddOneMonthToDate.  Since there is no
    -- such thing as a month with a ZERO, it rolls
    -- back to the last day of the prior month.
   
    -- if you were to use 1/29/2000,1/30/2000 or 1/31/2000
    -- as the date passed in an we add one month
    -- to that we would get 2/28/2000 back.  Since
    -- we told it to add one month, it only adds one
    -- month to and makes sure we get back a valid
    -- date.
  
    -- The @dayOfMonth that we then get from this
    -- is 28.
   
    -- We then subtract 28 from 2/28/2000.
   
    -- Since we can't have 2/00/2000 it goes to the
    -- prior day and the result in 1/31/2000.
    RETURN DATEADD(d, -@DayOfMonth, @AddOneMonthToDate)
      

    -- Of course we could just use this one line below
    -- to do all the work for us, instead of the previous
    -- five lines.  But then that wouldn't be fun, eh?
    /*
    RETURN DATEADD(d
                     , -DAY(  DATEADD(m,1,@date)  )
                     , DATEADD(m,1,@date)
                  )           
    */           

END

GO

-------------------------------------------------
--Now we will check to see if the code works
-------------------------------------------------

-- Should return 12/31/2011 
Select dbo.xGetLastDayOfMonth('2011-12-25')