"AreaZR via GitGitGadget" <gitgitgadget@xxxxxxxxx> writes: > From: Seija Kijin <doremylover123@xxxxxxxxx> > > If it is known that an int is either 1 or 0, > doing an exclusive or to switch instead of a > modulus makes more sense and is more efficient. FWIW, it is much more idiomatic in this codebase to say foo = !foo; to flip the polarity of foo when foo is used as a Boolean. It is both more readable than toggling only the bottom bit, and it is much more robust. Here 'used as a Boolean' means 'is it zero, or is it non-zero?', the norm used in the C language. If the reference to "foo", other than the place where the value of foo is consulted for the sole purpose of fliping between true-false, were to check if it is true or not, i.e. if (foo) do something; else do something else; then at this "real" use site, only the zero-ness of the value matters. foo==0 does something different from foo==1, but the code behaves the same way as the case where foo==1, if foo==2 or foo==3. But the code that flips by foo = 1 - foo; foo ^= 1; makes an assumption different from and stricter than the real use site. It only allows foo==0 and foo==1 without a good reason. But foo = !foo; keeps the same assumption as the real use site, which is why we prefer that form. And like it or not, it is natural to assume that 0 is false and everything else is true when writing in C, and especially in the codebase of this project. So let's not flip foo = !foo; into foo ^= 1; just to make it look different. Going the other way, or rewriting rewriting modulo 2 arithmetic into !foo form, would be more preferrable. The "flipped_block" is used like so: if (flipped_block && o->color_moved != COLOR_MOVED_BLOCKS) set MOVED_LINE_ALT bit in flags word; so it is very much Boolean whose zero-ness matters.
