Source code, reverse code, and supplemental code

Original code true Code

The original code is very simple. A 10-digit positive number is the binary number converted by the Division 2 method.

For example, the source code of 8 is: 1000

Reverse Code complement, bitwise NOT

It is also very easy, that is, to flip every bit. For example:

NOT 0111  (decimal 7)  = 1000  (decimal 8)

In C/C ++, use ~ Returns the inverse code.

One's Complement

This is a binary representation of a computer with signed integers. In short, positive numbers are the same, and negative numbers are reversed. The following example is from Wikipedia.

The table below shows all possible values in a 4-bit system, from −7 to + 7.

     +      - 0   0000   1111   Note that +0 and −0 return TRUE when tested for zero, FALSE when tested for non-zero. 1   0001   1110 2   0010   1101 3   0011   1100 4   0100   1011 5   0101   1010 6   0110   1001 7   0111   1000

This method is not commonly used due to some shortcomings.

Two's Complement

This is the most common method for computers to represent signed integers.

If a positive number is not changed, if a negative number is encountered, the binary value is reversed to 1, and overflow is ignored.

The table below shows all possible values in a 4-bit system, from −7 to + 7.

     +      - 0   0000      Note 0 has only one presentation:0000,no -0 1   0001   1111 2   0010   1110 3   0011   1101 4   0100   1100 5   0101   1011 6   0110   1010 7   0111   1001

This is the complement code.

Complement

The complement logic algorithm is: (positive numbers are the same, and the sign bit is 0)

1. The value of-7 (excluding symbols) is expressed as an integer of 111.

2. Add the symbol 1 to indicate a negative number, so it is 1111.

3. Only reverse the non-Signed bit, so it is 1000

4. Add 1, so 1001

Now let's see how the computer uses the two's Complement Algorithm to represent-7.

1.7 represents a bit of 00000111 (the number occupies at least one byte in the computer)

2. After the reverse is obtained, the result is 11111000.

3. After 1 is added, it becomes 11111001 (the high level is insufficient, and the computer uses the symbol bit to complement it)

The results are the same.