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Re: [Qemu-devel] [PATCH 1/2] bitmap.h: add comments to BITMAP_LAST_WORD_
Re: [Qemu-devel] [PATCH 1/2] bitmap.h: add comments to BITMAP_LAST_WORD_MASK
Mon, 30 Jul 2018 15:19:30 +0200
Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)
Wei Wang <address@hidden> wrote:
> On 07/30/2018 03:13 PM, Wei Wang wrote:
>> This macro was ported from Linux and we've reached an aggreement there
>> that the corner case "nbits = 0" is not applicable to this macro, because
>> when "nbits = 0", which means no bits to mask, this macro is expected to
>> return 0, instead of 0xffffffff. This patch simply adds a comment above
>> the macro as a note to users about the corner case.
>> Signed-off-by: Wei Wang <address@hidden>
>> CC: Dr. David Alan Gilbert <address@hidden>
>> CC: Juan Quintela <address@hidden>
>> CC: Peter Xu <address@hidden>
>> include/qemu/bitmap.h | 1 +
>> 1 file changed, 1 insertion(+)
>> diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h
>> index 509eedd..f53c640 100644
>> --- a/include/qemu/bitmap.h
>> +++ b/include/qemu/bitmap.h
>> @@ -60,6 +60,7 @@
>> #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) &
>> (BITS_PER_LONG - 1)))
>> +/* "nbits = 0" is not applicable to this macro. Callers should avoid that.
>> #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG -
>> #define DECLARE_BITMAP(name,bits) \
> A better fix would be to directly change the macro to: nbits ? (~0UL
>>> (-(nbits) & (BITS_PER_LONG - 1))) : 0,
> so that we don't need to fix other callers like bitmap_full,
> So just post this out for a discussion whether it's preferred to just
> adding note comments as we did for linux or fixing the macro directly.
On one hand:
a - we have copied it form linux, we don't want to diverge
On the other hand:
b - it is much easier to use if we change the macro
So, it is a tought one.
I slightly preffer b), but will not object to a either. As you are the
one doing the patch, your choice.