hey, hows it going?
i ripped this from the quake 3 source:
the code returns the reciprocal of sqrt(number).Code: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 ..........? 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; }
my question is this: what do they mean by "bit level hacking"? also, why is 0x5f3759df used?