When I read about collatz I wrote a C# program that short circuits the calculation like that, but my programming chops are not great and it could only handle 3000 digits of memory serves. It's somewhere on my GitHub page and I'm curious how many other people released similar code to speed things up.

I ended up using it to compare single core performance on any windows machine, because the timestamped logging was deterministic. Rewrote it in python and still use it these days.