REVEALED: The Quake III Secret Algorithm! Part 2

180821 Like and subscribe. This is an archive, check the link in the end if you are owner. When the Quake III Arena source code was released to the world it contained a previously unknown algorithm called the Fast Inverse Square Root. This is the story of this strange algorithm and how it works as told by retired Microsoft software engineer Dave Plummer.

For more info on the FISR:
A great video with better math explanations: https://youtu.be/p8u_k2LIZyo
A surprisingly complete and detailed Wikipedia article: https://en.wikipedia.org/wiki/Fast_inverse_square_root

Amazon Affiliate links for products mentioned in the video:
Zen of Code Optimization - https://amzn.to/2VO7ltx
Zen of Graphics Programming - https://amzn.to/3AxTAh9
Zen of Assembly [Out of Print] - https://amzn.to/2VD7Arn

Errata: If you find mistakes or important omissions, please let me know and I'll update this!

Credits: Thanks to my great-grandfather Plummer for standing in as Monte, and to viewer Brandon Pinske for the video topic suggestion!

00:00 Intro
00:35 Welcome
01:20 Recap
03:12 Racing Talk
05:30 Gates and Allen
08:20 Fixed Point
09:30 Floating Point
11:46 Historical Info
13:00 One Weird Trick
14:35 Constant Confusion
16:53 Race Prep
18:05 4 v 4
19:58 Conclusion
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