C language - bitwise operations

C语言中,Especially in embedded development,Bit manipulation is a very common knowledge point,Bitwise is involved（bit）The place of operation is also very common.
This article shares someCThe basics of bit manipulation operations in the language.

1、 位与操作（ & ）

First, the bitwise AND must be distinguished（&）和逻辑与（&&）,There seems to be a difference between the two,But the final result is completely different.
位与 & 的真值表：

从上表可以看出,位与 & The operating principle is ：Only if both objects involved in the operation are true（true 或 1）时,The result of the operation is obtained true 或 1 ,其它的都为flase 或 0.

位与 & In fact, it is to convert the two numbers involved in the operation into binary first,Then do the AND to get the result after the operation,如下：

 比如：0x01 & 0x03 = 0x01   // 运算如下： 
                          0x01：0 0 0 1                                                 
                          0x03：0 0 1 1                                                
                          结果：0 0 0 1    

2、 位或操作 （ | ）

First, the bitwise AND must be distinguished（|）和逻辑与（||）,There seems to be a difference between the two,But the final result is completely different.
位与 | 的真值表：

从上表可以看出,位与 | The operating principle is ：As long as one of the two objects involved in the operation is true（true 或 1）时,The result of the operation is obtained true 或 1 ,只有两个都是 0 才为 flase 或 0.

位与 | In fact, it is to convert the two numbers involved in the operation into binary first,Then do the AND to get the result after the operation,如下：

比如：0x01 & 0x03 = 0x03   // 运算如下： 
                          0x01：0 0 0 1                                                 
                          0x03：0 0 1 1                                                
                          结果： 0 0 1 1 

3、位取反操作（~）

Bit inversion is to convert the hexadecimal number to binary first,Then invert the corresponding bit(1 取反变为 0,0 取反变为1).比如：

比如：0x01 、 0x03  // 运算如下： 
                          0x01：0 0 0 1        ~ 0x01：1 1 1 0   = 0x0D                                          
                          0x03：0 0 1 1        ~ 0x03：1 1 0 0    = 0x0C 

4、位异或操作（ ^ ）

位异或 ^ 的真值表：

从上表可以看出,位异或 ^ The operating principle is ：When one of the two objects involved in the operation is true（true 或 1）时,The result of the operation is obtained true 或 1 ;如果两个都是 0 就为 flase 或 0;两个都是 1 就为 flase 或 0.总而言之就是：相同为0,不同为1.

比如：0x01 ^ 0x03 = 0x02   // 运算如下： 
                          0x01：0 0 0 1                                                 
                          0x03：0 0 1 1                                                
                          结果：0 0 1 0 

5、位移操作（<< 、>>）

displacement operation,Shift a few bits to the left to add a few bits to the right0,Shift a few bits to the right to add a few bits to the left0,The part outside the numerical range is discarded.如下：

比如：0x03  // 运算如下： 
                          0x03：0 0 1 1        右移1位：0 1 1 0    
                          0x03：0 0 1 1        右移2位：1 1 0 0
                          0x03：0 0 1 1        右移3位：1 0 0 0
                          0x03：0 0 1 1        左移1位：0 0 0 1
                          0x03：0 0 1 1        左移2位：0 0 0 0

6、Practical use of bit manipulation

6.1、Clear specific bits to zero

If you want to clear a bit of a specific number（置零）,Use bitwise AND & 进行操作.比如：

比如：0x0A = 1 0 1 0
Want to clear the second bit,The other bits remain unchanged,with bit and & 操作如下：
方法1：0x0A & 0x0D = 0x08
0x0A = 1 0 1 0
0x0D = 1 1 0 1
结果  ：1 0 0 0 = 0x08

方法二：0x0A & ~(1<<1)

6.2、to a specific location 1

If you want to clear a bit of a specific number（置零）,Use bitwise AND & 进行操作.比如：

比如：0x0A = 1 0 1 0
Want to be the first position 1,The other bits remain unchanged,with bit and | 操作如下：
方法1：0x0A | 0x01 = 0x0B
0x0A = 1 0 1 0
0x01 = 0 0 0 1
结果  ：1 0 1 1 = 0x0B

方法二：0x0A  |  (1<<0)

6.3、特定位取反

If you want to invert a bit of a specific number,使用异或 ^ 进行操作.比如：

比如：0x0A = 1 0 1 0
I want to negate the first bit,The other bits remain unchanged,Use bitwise XOR ^ 操作如下：
0x0A ^ 0x01 = 0x0B
0x0A = 1 0 1 0
0x01 =  0 0 0 1
结果  ：1 0 1 1 = 0x0B

注意：The XOR operation is the same as zero,不同为1operating principle！

6.4、Get a specific binary bit

If you want to get one or a few specific bits in a number,可以参考如下操作：

比如：0x0A = 1 0 1 0,Want to get the value of the second and third bits,可以按下面方法操作：
T = (0x0A >> 1) & 0x03 The resulting binary value is  0 1

If you want to get the fourth place,如下：
T = (0x0A >> 3) & 0x01 The resulting binary value is  1

其他的操作类似.

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