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+operators+only+on+unsigned+operands
>
> 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).

#define IS_ALIGNED(n,align)     (!((uint32_t)(n) & (align - 1)))