Wei Wang <wei.w.w...@intel.com> 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 <wei.w.w...@intel.com> >> CC: Dr. David Alan Gilbert <dgilb...@redhat.com> >> CC: Juan Quintela <quint...@redhat.com> >> CC: Peter Xu <pet...@redhat.com> >> --- >> 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 - >> 1))) >> #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, > bitmap_intersects. > > 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. > > Best, > Wei
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. Later, Juan.
