Fast Inverse Square Root – A Quake III Algorithm:
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| 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; | |
| } |