Carmack is a smart guy, and there's no question that he's amazing at optimization, but his code is pretty messy, especially early versions. In the Doom engine,

Carmack is a smart guy, and there's no question that he's amazing at optimization, but his code is pretty messy, especially early versions. In the Doom engine, for example, he has hard coded lots of things directly in the C engine code that really should be part of the regular game code.