I learned one method in high school. I couldn't remember it, and too lazy to try...

Nav_Panel · on March 6, 2013

I just want to point out one of the links on that page: http://en.wikipedia.org/wiki/Fast_inverse_square_root

Absolutely hilarious and amazingly magical method of algorithmically computing square roots. It right shifts a floating point number to essentially divide the exponent component by 2. Then it uses a weird magic number trick to get the correct result. Awesome random programming trivia.

ars · on March 6, 2013

Note that this is the inverse square root, i.e. 1/sqrt(x) (which can also be written x^(-1/2) ).