Oracle number format model maximum length

Question

I run into a peculiar limit in X number format element used in to_numberand in to_char when I was converting hexadecimal numbers to decimal numbers.

It looks like number format model has maximum length of 63 characters but I can't find the limit mentioned in the docs. E.g. the maximum length of datetime format model is mentioned:

The total length of a datetime format model cannot exceed 22 characters.

With 63 Xes:

SQL> select to_number('A', rpad('X', 63, 'X')) from dual;

TO_NUMBER('A',RPAD('X',63,'X'))
-------------------------------
                             10

With 64 Xes:

SQL> select to_number('A', rpad('X', 64, 'X')) from dual;
select to_number('A', rpad('X', 64, 'X')) from dual
                      *
ERROR at line 1:
ORA-01481: invalid number format model

I have only tried X format element as it is relevant for my current task.

The questions:

1. Is this a known number format model limitation that is just missing from documentation ?
2. How do I convert a 64 (and longer) digit length hexadecimal number to a decimal number ?

Answer 1

It's beyond precision NUMBER can go. More info in official documentation: http://docs.oracle.com/cd/E16655_01/server.121/e17209/sql_elements001.htm#SQLRF00222