Introduction to original code, inverse code and complement code

Signed number , The first bit on the left is the sign bit ,0 Being positive ,1 Negative . stay java All of them are signed numbers .

##. Switch relationships

Original code ： The leftmost is the sign bit , Use the remaining digits to represent the absolute value ;

Inverse code ： Positive sum 0, The inverse code is itself ;

           The inverse of a negative number , The sign bits remain the same , The other figures are reversed （0 change 1,1 change 0）.

Complement code ： Positive sum 0, The complement is itself ;

            A negative complement , On the basis of irony , Regardless of sign bit , Last digit plus 1.

##.java Transform in code

Bit operations are available in code , Original code to inverse code , With int Value, for example , if a Is a negative integer , be a The inverse of is ：

int b = a ^ Integer.MAX_VALUE;

or     int b = -(~a);

notes ：java Median operation , Can also do operations on sign bits .

The complement is ：b = b-1;  // because b It's a negative number , So the last one adds 1, Equal to minus in truth 1.

Truth value ： Signed number , Regardless of sign bit , The value of the number composed of the remaining digits , Equal to the absolute value of the truth

With java in byte Type positive numbers as an example ：

Decimal system	Original code	Inverse code	Complement code
1	0000 0001	0000 0001	0000 0001
-1	1000 0001	1111 1110	1111 1111
0	0000 0000	0000 0000	0000 0000
-128（Byte minimum value ）	1000 0000	1111 1111	1000 0000
127（Byte Maximum ）	0111 1111	0111 1111	0111 1111