Quake III & the reciprocal square root

In the C source code of the famous game “Quake III — Arena” you can find an incredibly efficient piece of code that seems totally insane and incomprehensible! It is the code for computing the…

The Apache Groovy programming language - Blogs - Quake III Arena

Quake III Arena - Wikipedia

Quake III Arena - Wikipedia

Fast reciprocal square root in 1997?! - Shane Peelar's Blog

Behind the Performance of Quake 3 Engine: Fast Inverse Square Root

Math or Game Developers - Fast Inverse Square Root

Quake: John D. Carmack, Id Software, QuakeC, Quake II, Quake III

Has anyone ever had a eureka moment like the fast inverse square

Behind the Performance of Quake 3 Engine: Fast Inverse Square Root

2. Now write the function to calculate the inverse