UNIX time system in SQL SERVER

CREATE FUNCTION [dbo].[UNIX_TIMESTAMP] (
@ctimestamp datetime
)
RETURNS integer
AS 
BEGIN
  /* Function body */
  declare @return integer

  SELECT @return = DATEDIFF(SECOND,{d '1970-01-01'}, @ctimestamp)

  return @return
END



ALTER FUNCTION [dbo].[FROM_UNIXTIME] 
(
	-- Add the parameters for the function here
	@ctimestamp int
)
RETURNS smalldatetime
AS
BEGIN
	-- Declare the return variable here
	DECLARE @ctimestamp2 smalldatetime

	-- Add the T-SQL statements to compute the return value here
	select @ctimestamp2 = DateAdd(ss, @ctimestamp, '1970-01-01')

	-- Return the result of the function
	RETURN @ctimestamp2

END