Origin of Quake3's Fast InvSqrt()

This code was written when the software industry looked very different. Particularly, the teams were super tiny, and cleverness won out over code clarity every time due to the relatively weak computation power that was readily accessible. I would have been surprised to hear that any of the dirty/genius hacks found in apps written in the 80's and early 90's was well documented.

That good sqrt code made it into Quake 3 from previous codebases is also not surprising. If it ain't broke...