Demystifying bitwise operations, a gentle C tutorial

Re:Demystifying bitwise operations, a gentle C tutorial by layer8 on Friday March 03, 2023 @02:46PM (#35014139)

This is one case where lining up values (and surrounding operators with spaces) can be good practice:

    tx_data[43] = utime >> 24;
    tx_data[44] = utime >> 16;
    tx_data[45] = utime >>  8;
    tx_data[46] = utime >>  0;

Or even:

    tx_data[43] = utime >> (3 * 8);
    tx_data[44] = utime >> (2 * 8);
    tx_data[45] = utime >> (1 * 8);
    tx_data[46] = utime >> (0 * 8);

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Re:Demystifying bitwise operations, a gentle C tutorial by mtlmtlmtlmtl on Friday March 03, 2023 @05:55PM (#35016149)

Yep. Bugs like this just pop out at you this way.

Having spent a lot of time digging into C code and doing microcontroller programming professionally, I have learned a certain disdain for the practice of using minimal whitespace in expressions, and the related practice of minimising LOC using C's very dense expressions syntax(unary dec/inc operators, the fact that assignment is itself an expression, etc).

The dense expressions syntax is pretty much a holdover from the time C was invented by Dennis Ritchie for the purpose of porting Unix; when it had to be typed on a painfully slow electromechanical teletype. This is also why most Unix commands are 2-4 characters long.

But it serves very little meaningful purpose today. It's important to remember that you might be able to turn 3 lines of code into 1, but it'll still be the same amount of machine code. And it will probably be harder to read, harder to change, and harder to reason about. And it can be a lot easier to miss some edgecase or even a typo like in this case. I have seen such a silly amount of off-by-one errors in C code due to some subtle misuse of unary increment/decrement that I stopped using those operators altogether. They don't improve your software in any meaningful way.

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Re:Demystifying bitwise operations, a gentle C tutorial by ziml77 on Friday March 03, 2023 @08:30PM (#35017218)

I've done the >> 0 thing to make it very clear what's going on, but I hadn't considered the * 8 construction. That's actually easier to comprehend at a glance because the numbers become less "magic". (8 and 16 are obvious to me, but 24 always has me second-guessing myself somewhere in the back of my mind)

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Re:Demystifying bitwise operations, a gentle C tutorial by lolcatuser on Saturday March 04, 2023 @01:19PM (#35023049)

I use octal for this.

  x << (3 * 8);

vs.

  x << 030;

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