Cool Hack Of The Day Grand Opening!

Based off of this reddit thread, Cool Hack Of The Day is now live! The site won't be able to stay alive without your help, so please email your best examples of coding prowess to chotd.feedback@gmail.com.


We'll start the site with one of the more legendary hacks ever seen - Carmack's Inverse Square Root.

float Q_rsqrt( float number )
{
long i;
float x2, y;
const float threehalfs = 1.5F;

x2 = number * 0.5F;
y  = number;
i  = * ( long * ) &y;  // evil floating point bit level hacking
i  = 0x5f3759df - ( i >> 1 ); // what the fuck?
y  = * ( float * ) &i;
y  = y * ( threehalfs - ( x2 * y * y ) ); // 1st iteration
// y  = y * ( threehalfs - ( x2 * y * y ) ); // 2nd iteration, this can be removed

#ifndef Q3_VM
#ifdef __linux__
 assert( !isnan(y) ); // bk010122 - FPE?
#endif
#endif
return y;
}

A more thorough history of this code can be found here.