Is it safe to do a TO_NUMBER(TO_CHAR(:n)) ?
var n number
exec :n := 9.9999999999999999999999999999999999e125
select to_number(to_char(:n)) from dual;
ORA-01722: invalid number
If a positive NUMBER value is extremely large and cannot be represented in the specified format, then the infinity sign (~) replaces the value
select to_char(:n) from dual;
I wrote more about infinity here