## November 30, 2009

### I’m enrolling for PhD

Guest question from Logik. Thanks dude! Your GQHero trophy has been delivered to your house ;)

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Cracked by: **sidsen ** , Raghuvansh , Jean Valjean , krudebox , Dibyo , yaksha , Logik , shashank , shrik , Ps , SV , joe , udupendra , shenoyvarun86 , Rogi , p vs np , byslexia , AC , akhi , umang , madhur , Anubhav and Ananth

Answer:

The super fast inverse square root function from Q3A. Contrary to what many of you think, this piece of code was _not_ written by Carmack. See this http://www.beyond3d.com/content/articles/8/

Quoting Logik for details

The strip makes a reference to the Newton method for calculating inverse square roots.

from:

http://www.explainxkcd.com/2009/11/18/academia-

vs-business/

0Ã—5f375a86 is the value used in the algorithm to approximate the solution to the square root of an unsigned floating number, also known as fast inverse square root.

The solution uses an ingenious first approximation and the difficult problem was solved without any fanfare (like in the cartoon) for the game, Quake III Arena.

0Ã—5f3759df is also used, which is found to be less accurate.

http://en.wikipedia.org/wiki/F…..quare_root

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