docs: public void cross(Vector3d v1, Vector3d v2) {
          double tmpx = v1.y * v2.z - v1.z * v2.y;
          double tmpy = v1.z * v2.x - v1.x * v2.z;
          double tmpz = v1.x * v2.y - v1.y * v2.x;
  
          x = tmpx;
          y = tmpy;
          z = tmpz;
      }