Re: [Qemu-devel] [PATCH 1/2] bitmap.h: add comments to BITMAP_LAST_WORD_MASK
On 07/30/2018 09:19 PM, Juan Quintela wrote: Wei Wang 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 0x. This patch simply adds a comment above the macro as a note to users about the corner case. Signed-off-by: Wei Wang CC: Dr. David Alan Gilbert CC: Juan Quintela CC: Peter Xu --- 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. Thanks Juan. I plan to choose b - fixing the macro directly. Best, Wei
Re: [Qemu-devel] [PATCH 1/2] bitmap.h: add comments to BITMAP_LAST_WORD_MASK
Wei Wang 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 0x. This patch simply adds a comment above >> the macro as a note to users about the corner case. >> >> Signed-off-by: Wei Wang >> CC: Dr. David Alan Gilbert >> CC: Juan Quintela >> CC: Peter Xu >> --- >> 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.
Re: [Qemu-devel] [PATCH 1/2] bitmap.h: add comments to BITMAP_LAST_WORD_MASK
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 0x. This patch simply adds a comment above the macro as a note to users about the corner case. Signed-off-by: Wei Wang CC: Dr. David Alan Gilbert CC: Juan Quintela CC: Peter Xu --- 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
[Qemu-devel] [PATCH 1/2] bitmap.h: add comments to BITMAP_LAST_WORD_MASK
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 0x. This patch simply adds a comment above the macro as a note to users about the corner case. Signed-off-by: Wei Wang CC: Dr. David Alan Gilbert CC: Juan Quintela CC: Peter Xu --- 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) \ -- 2.7.4
