finite-field arithmetic

The idea of the fast method is independent on the optimization of finite field arithmetic and the choice of coordinate expression of points of elliptic curves.
实现了算法的快速优化，其原理与有限域算术优化和椭圆曲线点的坐标表示的选取无关，其运算速度是通常的重复加倍—点加算法的6倍。