Below is alternative method that's closer to the original technique (for good or ill).  Btw, there's a minor bug in the other code that doesn't reduce the day count if the first date has a later time than the second date.

SELECT *
FROM (VALUES
    ('2017-10-01 10:46:00', '2017-10-17 01:45:00'),
     ('2017-10-17 10:46:00', '2017-10-01 01:45:00')
) dates(date1,date2)
CROSS APPLY dbo.ifn_DifferenceBetweenDates( date1, date2 )
CROSS APPLY dbo.ufn_DifferenceBetweenDates2 ( date1, date2 )


CREATE FUNCTION dbo.ufn_DifferenceBetweenDates2
(
  @Date1 datetime, --Dia inicio
  @Date2 datetime --Dia fin
)
RETURNS TABLE
AS
RETURN (
  SELECT CAST(CAST(dias AS varchar(5)) + 'd ' +
   CONVERT(varchar(8), DATEADD(SECOND, segundos, 0) , 8) AS varchar(16)) AS DiferenciaenHoras
  FROM (
   SELECT CASE WHEN @Date1 > @Date2 THEN 0 ELSE DATEDIFF(SECOND, @Date1, @Date2) / (60*60*24) END AS dias,
     CASE WHEN @Date1 > @Date2 THEN 0 ELSE DATEDIFF(SECOND, @Date1, @Date2) % (60*60*24) END AS segundos
  ) AS cálculos
)
GO