Basic syntax - bit operation

Displacement

• The data stored in memory moves left and right according to binary bits .

1. Move right ( Binary data moves to the right ) The operator ：>>
2. Move left ( Binary data moves to the left ) The operator ：<<

• Examples of use

int a = 1;
int b = a << 1; // Move left 1 position 
int c = a >> 2; // Move right 2 position 

C Language processing standards

• Move left ： Shift and right padding
• Move right ： There are two ways to do this

1. Unsigned numbers are logically shifted right ： Shift and left padding
2. Signed numbers are arithmetically shifted right ： Shift and left complement sign bit （ Positive complement 0, Negative numbers make up 1）.

• Example ：

unsigned int a = 0xFFFFFFFF;
int b = 0xFFFFFFFF;

printf("%x\n", a << 1);
printf("%x\n", b << 1);
printf("-----------------\n");
printf("%x\n", a >> 1);
printf("%x\n", b >> 1);

*  Running results ：
fffffffe
fffffffe
-----------------
7fffffff
ffffffff

Why is there only one processing method for shift left , The right shift is divided into logical right shift and arithmetic right shift

• Because left shift is often used in multiplication （ Moving one bit to the left is equivalent to multiplying by 2）, Shift right is often used in division operations （ Moving one bit to the right is equivalent to dividing by 2）.
• Move left （ multiply 2 After multiple of ） If the data overflows to the sign bit （ The first one on the far left ）, Neither signed number nor unsigned number can be represented , Data overflow cannot be avoided , So the left shift is handled uniformly , Moving right does not cause data overflow , To ensure the right shift （ Divide 2） The correctness of the arithmetic result of , You cannot change the sign of a signed number , for example ： Signed number -8 Move right 1 Bit divided by 2 The correct answer should be -4, Therefore, the processing method for signed numbers is called arithmetic shift , Unsigned numbers have no sign , Just fill in the zero by logic , So it's called logical shift right .