I have a regular expression that throws ORA-12733, "regular expression is too long". How do I determine what the maximum supported size is?

FYI: the offending regex is 892 characters. It's a generated regex, so I could change how I generate and execute it, but I would like to know what the limits to the max size are before I change how I am generating and executing.

(running Oracle 10.2g)

UPDATE:

If it depends on the actual regex, here's the begining of it (the rest is just the same thing repeated, with different values between ^ and $):

(^R_1A$|^R_2A$|^R_3A$|^R_4A$|^R_4B$|^R_5A$|^R_5B$...