FLOOR and CEIL bug ??

I have made this query:
select (90523434-31289)/(90492145/19)
Division,floor((90523434-31289)/(90492145/19)) Floor,ceil((90523434-31289)/(90492145/19)) Ceil from dual; and the resul is :
Division Floor Ceil
---------- ---------- ----------

        19 18 19

For me there is a Oracle bug. What do you thing ??
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Gambelli Domenico
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