one's Complement表示按位取反；
two's Complement表示按位取反后再加1

1的补码可以认为只有一步操作的补码，按位取反

2的补码可以认为有两步操作的补码，，按位取反后，再在最低位加1。

To get 1’s complement of a binary number, simply invert the given number.

To get 2’s complement of a binary number, simply invert the given number and add 1 to the least significant bit (LSB) of given result.