> > #define is_power_of_two(x) (!((x) & ((x)-1))) > > #define low_bit_mask(x) (((x)-1) & ~(x)) > > #define is_contiguous_mask(x) is_power_of_two(1 + (x) + low_bit_mask(x)) > > Side note: I didn't check this. So if you actually do this, please > double-check. The math should all be good, but there's a few caveats: Checked, and seems to work. Even sparse appears to be very happy. :) I'll do some more extensive testing later today before submitting a patch. > The "zero is special" thing means that if you don't want to accept zero as > a valid mask (it technically *is* a contiguous set of bits set - it's just > the empty set) you'd need to check for it specially. Good point, I'll add a check for that as well. > Thus endeth Linus' "games with bits" lecture. It was probably more than > you really wanted to know. There's a ton of games you can play with simple > "x-1" and bitmasking ops like this). Thanks, for both the macro's and the lecture. ;) Ivo - To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
