"using '!' logical when bitwise '~' was probably intended" C-CodePudding

Hi I am trying to adapt some code I found online for calculating a parabolic SAR https://github.com/TulipCharts/tulipindicators/blob/master/indicators/psar.c. Being C it runs fine. But I get a green ziggy line under the !lng saying "using '!' logical when bitwise '~' was probably intended".

If I change from lng = !lng; to lng = ~lng; it computes the incorrect output. So I have left it as the original code.

But I was wondering how I can fix this / update it to C so I don't have the "error" message, and also what is the difference in CPP between! and ~ and why does it cause a difference in the outputs, Many Thanks.

        if ((lng && low[i] < sar) || (!lng && high[i] > sar)) {
            accel = accel_step;
            sar = extreme;
            lng = !lng;
            if (!lng) extreme = low[i];
            else extreme = high[i];
        }

CodePudding user response：

A couple of things to clear up confusion:

If you change the line lng = !lng to be lng = ~lng, here's what happens. If the value of lng is 0, the bitwise complement will give you 0xffffffff, assuming a 32-bit integer. If this value is used in a boolean check, it will evaluate to "true" because it's non-zero. If the value of lng is 1, the bitwise complement will give you 0xfffffffe, which will also evaluate to "true" in a boolean check, again because it's nonzero. This is why it breaks your code.

If you want to compile with a C compiler, you can change the type of lng to bool as others have suggested. If you're planning to stick with C, you can also use bool, but you'll need to first #include <stdbool.h>, and make sure you're compiling with a C version greater than or equal to C99.

Another way to fix this is just to use an xor with 1 whenever you want to invert the value. So instead of lng = !lng (which the compiler expands logically to lng = (lng != 0) as @BenVoigt pointed out), you can do lng ^= 1. This allows you to continue treating lng as an integer numeric value (i.e. not a bool in the strictest sense) and thereby get rid of the warning without changing much else.

CodePudding user response：

Since we now know that the green ziggy in question is displayed in VS 2022, it's possible to formulate an answer.

I think this warning is just noise personally - that code is perfectly legitimate as it was - but fortunately there's a way to turn it off. Just change:

Options -> Text Editor -> C/C -> Code Style -> Linter -> Logical/Bitwise Mismatch

to None and you're done.