C language sets/gets the value of a certain bit in a variable

lugl4313820

C language sets/gets the value of a certain bit in a variable [Copy link]

 

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In operating registers, you need to set/get the value of a certain bit.

#define GetBit(m,n) ((m)>>y)&0x01) //Get the value of the nth bit of m and return 0 or 1

#define SetBit(m,n) m |= (1<<n) //Set the n bit of m to 1

#define ClrBit(m,n). m &= ~(1<<n) //Clear bit n of m

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1nnocent

Haven't come across any collections yet.

。

xutong

Reminded me of the bit operation of the msp430 microcontroller

well_kim

Learned

henangongda-123

Learned, collected

吾妻思萌

Directly operate on the address according to the memory bit operation

lugl4313820

Azuma Simeng published on 2023-1-23 21:21 Directly operate on the address according to the memory bit operation

Happy New Year, moderator. Have you been to your father-in-law's house? How's the effect? Are you ready to make a bunny?

yang_alex

The basic operations of embedded systems in the 51 era were mainly due to the small amount of memory at that time. Now that MCUs have large memory, some operations are no longer done this way.

lugl4313820

yang_alex posted on 2023-1-24 08:50 The basic operations of embedded systems in the 51 era were mainly due to the small amount of memory at that time. Now that MCUs have large memory, some of them are no longer done this way.

Is it faster to use bit operations? Some hal libraries now require many judgments, which means the programming speed is high but the efficiency is not high.

Jimmy_Arareb

lugl4313820 posted on 2023-1-24 12:49 Is it faster to use bit operations? Some hal libraries now have to judge many times, and the programming speed is high, but the efficiency is not high.

The low efficiency of the hal library is a thing of the past. After modern compilers enable o1 local optimization, these expressions inside the hal library will be optimized out, and the efficiency is basically the same as writing directly to registers. On the contrary, the portability and readability of the hal library are much better than the standard library and registers. In addition, if the timing requirements for io operations are relatively high, microcontrollers that support bit-band operations can use bit-band operations, which is much faster than reading registers, doing bit operations, and then writing.

yang_alex

lugl4313820 posted on 2023-1-24 12:49 Is it faster to use bit operations? Some hal libraries now have to judge many times, and the programming speed is high, but the efficiency is not high.

Yes. Bit manipulation is faster and is very convenient for making flags (formerly called flag bits) for multi-conditional compound judgments. The main frequency of MCUs is generally high now, and most of our needs can be met. Bit manipulation is only performed when the performance of the MCU needs to be squeezed, and in extreme cases, assembly language may be used for bit manipulation. The disadvantage of bit manipulation is that the code is more cumbersome to read (in fact, C language is not bad, you can name the variables yourself and it reads the same), and you need to be familiar with bit shift operations.

盛世辉煌电子科学

Learned

lugl4313820

yang_alex posted on 2023-1-25 09:31 Yes. Bit operations are faster and are very convenient for making flags (originally called flag bits) for multi-conditional compound judgments. Now the main frequency of MCU is generally...

Studying bit operations can change your programming ideas. Some things that can be done in one sentence may require a lot of detours if you use a library. I wonder if you don't need to convert them after compiling.

pcf2000

I am more accustomed to bit operations, which are simple, direct and transparent. . .

lugl4313820

pcf2000 posted on 2023-1-31 10:51 I am more accustomed to bit operations, which are simple, direct and transparent. . .

I didn’t understand it before, but later on, I finally figured it out and it felt like it was going on pretty quickly.

郑小气聋子

When I was learning 32 register programming, I started to get used to operating bit by bit.

半导体小白

Simple, direct, clear, and efficient. This is how 51 is basically operated. It has many logical operations and high operating efficiency.