SQL Server - Get the First day of a given week

The first of several Date functions that I've created to determine certain dates.

This one will return the first day of a week based upon the date you pass in.

-------------------------------------------------
-- Does the function already exist?
-- if so... drop it.
-------------------------------------------------
IF OBJECT_ID(N'dbo.xGetFirstDayOfWeek',N'FN') IS NOT NULL
BEGIN
    print 'Function found... Dropping'
    DROP FUNCTION dbo.xGetFirstDayOfWeek
END

GO

CREATE FUNCTION dbo.xGetFirstDayOfWeek(@Date DateTime)
RETURNS DateTime
AS





-------------------------------------------------
--Function will return the first day of the
--week based upon the date passed in.
--
--You pass in a Date and it return
--the Date for first day of the week
-------------------------------------------------
BEGIN

    DECLARE @DayOfWeek      INT
    DECLARE @DaysToSubtract INT

    -- Get the day of the week
    -- i.e. if today is Thursday and the week starts on Sunday
    --      then the day of the week is 5
    SET @DayOfWeek = DatePart( dw, @Date )
   
   
   -- We need to subtract one from the @DayOfWeek.
   -- The reason is that if today is the 5th day and we want
   -- to get back to the 1st day, we only need to subtract 4
   -- from the Date.  Otherwise we would end up at 0.
   SET @DaysToSubtract = @DayOfWeek -1


   -- Now we subtract @DaysToSubtract from the @date passed in.
   -- This will return the first day of the week for the given @date.
    RETURN DATEADD( d, -@DaysToSubtract, @Date )


    -- Instead of the previous five lines of code we could 
    -- have also used this single line.  I broke it out above to
    -- hopefully better explain what was happening.
 
    -- RETURN DATEADD(d,-(DATEPART(dw, @Date) - 1),@Date)
END

GO

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

-- Should return 11/27/2011

Select dbo.xGetFirstDayOfWeek('2011-12-01')

 

-- Should return 12/25/2011 --already the first day of the week
Select dbo.xGetFirstDayOfWeek('2011-12-25')