Java has BigDecimal in the standard library. That gives you arbitrary precision. Also, using a double instead of a float gives you a bit better precision. The performance hit of using double instead of float on modern hardware is not something that should be a showstopper.

I don't get the argument about libraries and performance. We're talking about companies using emulators of ancient hardware to run decades old software. Pulling in some library is a complete non issue from a performance point of view.

Speaking of hardware, that is magnitudes faster than anything imaginable when most cobol was first written. Performance is not the key concern here.