左位移几就相当于乘以2的几次方( Left bit shifting to multiply by any power of two )
//将一个值向左侧移动一位与这个值乘以 2 等效 。浮点数通过舍去小数点后面的所有位来转换为整数。
大约快了300%
x = x * 2;
x = x * 64;
//相当于:
x = x << 1;
x = x << 6;
右位移几就相当于除以2的几次方(Right bit shifting to divide by any power of two)
//将一个值右移