get shape volume 요거안에서 저거 쉬프트시키고 저러는걸로 어떻게 부피구하는거에요?? r^3*4/3 이게 체적구하는거잖아 모르겠음 왜저런거임?

double get_circle_volume(const doubleradius, const unsigned int attempts){    unsigned int count = 0;    for (unsigned int i = 0; i < attempts; ++i)    {        int x = (rand() << 1) - RAND_MAX;        int y = (rand() << 1) - RAND_MAX;        count += x * x + y * y <= (RAND_MAX * RAND_MAX);    }    return (count << 2) * (radius *radius) / attempts;}
double get_sphere_volume(const doubleradius, const int  attempts){    returnget_circle_volume(radius, attempts) * 4. / 3. * radius;}