What's new

The Fast Inverse Square Root: A Quake III Algorithm

aphexlox

Registered User
Registered User
Member
Joined
Oct 4, 2021
Messages
11
Reaction score
1
Gender
Male
For all you C nerds out there, I found a great video on the famous Fast Inverse Square Root algorithm pulled from ID Software's Quake III Arena source code. Check it out!


For those that want a preview, here it is:

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; }
 
Top