- Published on
Doom's magic function
- Authors
- Name
- Agam More
- @agammore
This is just my first post.
Why?
Every personal site needs a first post, no?
Nothing interesting?
Ok, ok... Here is a magnificent peice of code I like:
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
return y;
}
At the time, floating-point division was generally expensive compared to multiplication; the fast inverse square root algorithm bypassed the division step, giving it its performance advantage. Quake III Arena, a first-person shooter video game, used the fast inverse square root algorithm to accelerate graphics computation...
Source: Wikipedia