Re: [Libguestfs] [PATCH nbdkit v2] common: isaligned: Use a macro instead of relying on implicit truncation.

On 9/17/18 3:39 PM, Nir Soffer wrote: >> +#define IS_ALIGNED(size, align) ({ \ >> + assert (is_power_of_2 ((align))); \ >> + !((size) & ((align) - 1)); \ >> +}) >> > > But this version will happily accept singed int, and I think this code > behavior with signed int is undefined. Well, sort of. Bit shifts are very likely to hit undefined behavior on ints. But & and | are not shifts. > > See > https://wiki.sei.cmu.edu/confluence/display/c/INT13-C.+Use+bitwise+operat... > > Why use a macro when we can use a function that is likely to be inlined > anyway? > This is not used in tight loops, so there is no reason to use a macro. > > If you want to use a macro, see the kernel align macros: Alas, the kernel has a more restrictive license (GPLv2 in general); which means we can't copy it into nbdkit. (True, the definitions will look similar, but if we claim we copied from somewhere, that source had better be permissively licensed).