float Q_rsqrt( float number )
{
  long i;
  float x2, y;
  const float threehalfs = 1.5F;
   
  x2 = number * 0.5F;
  y  = number;
  i  = * ( long * ) &y;                        
  i  = 0x5f3759df - ( i >> 1 );          
  y  = * ( float * ) &i;
  y  = y * ( threehalfs - ( x2 * y * y ) );    
   
  return y;
}