Oracle gets two-date-difference hours ____oracle

In the project to find two days difference in the number of hours, with ceil the hour data is wrong, study the ceil (n) function, found that the function is more than equal to the number N of the smallest integer, which is very likely to have the problem of divisors, after testing round () function and To_number () The relative and Ceil functions are accurate.

--ceil ()
Select Ceil (to_date (' 2016-09-01 ', ' yyyy-mm-dd HH24 ')-to_date (' 2016-08-31 ', ' yyyy-mm-dd HH24 ') *24 ) +1 from 
  dual;
   
--round ()
Select round (to_number to_date (' 2016-09-01 ', ' yyyy-mm-dd HH24 ')-to_date (' 2016-08-31 00 ', ' Yyyy-mm-dd HH24 ')) *24) +1 from 
  dual;