pre:

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 gently caress?
 	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;
 }