Bit operation

Bit operators , It mainly includes
And , or operator &,|
Inverse character ~
Shifter <<,>>
XOR ^

Before we start, let's look at a piece of code to realize binary output , The observation position is convenient
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void printf_bin(int num)
{
    
    int i, j, k;
    unsigned char *p = (unsigned char*)&num + 3;//p Point first num Next 3 Byte address , namely num The highest byte address of 

    for (i = 0; i < 4; i++) // Sequential processing 4 Bytes (32 position ）
    {
    
        j = *(p - i); // Take the first address of each byte , From high byte to low byte , namely p p-1 p-2 p-3 address 
        for (int k = 7; k >= 0; k--) // Processing of each byte 8 bits , Note that the binary number inside the byte is stored according to people's habits ！
        {
    
            if (j & (1 << k))//1 Move left k position , And the byte content before the single j Or operation , Such as k=7 when ,00000000&10000000=0 -> The highest bit of this byte is 0
                printf("1");
            else
                printf("0");
        }
        printf(" ");// Every time 8 Bit plus a space , Convenient view 
    }
    printf("\r\n");
}

And operators &

And 0 clear 0, And 1 unchanged

function 1： Extract bit data
function 2： eliminate （0）

e.g.

#include <stdio>

int main()
{
    
	// take int The variable of a Of the 28 Positional clarity 0, Other bits remain the same 
	int a = 0xffffffff;
	a = a & 0xefffffff;
	printf("a = 0x%x\n", a);
	printf_bin(a);
	
	// take int The variable of b Of the 17 Positional clarity 0, Other bits remain the same 
	int b = 0xffffffff;
	b = b & 0xfffdffff;
	printf("b = ");
	printf_bin(b);
	
	return 0;
}

Or operator |

or 1 Set up 1, or 0 unchanged

function ： Set up 1

Example ： take int The variable of a Of the 22-23 Location 1, Other bits remain the same

int a ; 

a = a | 0xc00000

Negation operator ~

Take the opposite 1 Turn into 0, Take the opposite 0 Turn into 1

Example ： take int The variable of a Of the 28 Positional clarity 0, Other bits remain the same

 a = a & ~ (0x10000000);

Shift Operators << / >>

The shift operator shifts to the left / Move right
The leftmost position when moving left （ Include sign bits ） Move out of memory space , The rightmost digit is filled with zero
When moving right, the rightmost bit is removed , Leftmost zeroing

char c = 0x80 = 0b 1000 0000 

a = a & ~(0x1<<28)
a &= ~(0x1<<28);

a = a + 3; 
a += 3; 

a = a & ~(0x3<<26);

Move left and right circularly, and the leftmost bit is connected with the rightmost bit （ Bit operation cannot be realized )

Exclusive or operator ^

Exclusive or 1 Take the opposite , Exclusive or 0 unchanged

Example ： take a Of the 28 Bit exclusive or 1, the a Of the 28 Bit inversion
And Take the opposite ~ The difference between lie in Exclusive or ^ Of Direct action object by a No 28 position

 a = a ^ (0x1<<28);

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Original code 、 Inverse code 、 Complement code