The last comment in the issue (as of this posting) posted to a comment from John Carmack on Twitter: https://twitter.com/ID_AA_Carmack/status/1254872368763277313

I specialise in legacy code. I've seen my fair share of abysmal code that works. This is pretty awful, but far from the worst I've ever seen in my career -- even in systems where public safety was critical. I've not looked at this code in any real detail, but I suspect John Carmack (who has doubtless seen a fair amount of complex C code in his life) has it right.

On the plus side, if anyone wants to practice refactoring gnarly C code: here's your opportunity.