They missed the 3rd(!) bug in those few lines of code? The normalization was done before zeroing out the Z component, so the resulting vector isn’t actually normalized.
Not saying I never conjure the spaghetti but whoever coded that really was deep into the tail end of a caffeine, coding and sleep deprivation binge ;)
Good chance it was John Carmack, probably one the top 10 programmers of all time. He basically built the Quake engine himself. There is a pretty decent analysis of it here:
* https://fabiensanglard.net/quakeSource/index.php
I recommend checking it out.
EDIT: i was thinking of the analysis done on Quake 2, which is more about the engine:
* https://fabiensanglard.net/quake2/index.php
while the one about is regarding the multiplayer system, which is still an amazing bit of dev.
Github: