[31b3r3t7]

No need for runtime polymorphism for this. The same binary won't be used in different operating systems. This is a classic example of misuse of C++ features just because they exist and a reason why I personally prefer programming in C. What I would do in a case like this is to have three source files each implementing the function for UNIX/Windows/Mac and the build system should take care of compiling the right one into the program depending on the OS.

[delta_p_delta_x]

This is a much better idea, actually. You're right that what I mentioned is a bad misuse of C++ features.

I initially did think of simply letting the build system handle it (CMake can do this excellently, as can Meson, probably) by simply choosing different source files for different target OSs, but when typing out the parent comment, I forgot about it in my train of thought.

Come to think of it, this is far more elegant.