From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41658) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fkQXz-00036N-DE for qemu-devel@nongnu.org; Tue, 31 Jul 2018 05:02:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fkQXu-00044f-HL for qemu-devel@nongnu.org; Tue, 31 Jul 2018 05:02:27 -0400 Received: from mga17.intel.com ([192.55.52.151]:54422) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fkQXu-00042s-5q for qemu-devel@nongnu.org; Tue, 31 Jul 2018 05:02:22 -0400 Message-ID: <5B60269E.4040601@intel.com> Date: Tue, 31 Jul 2018 17:06:38 +0800 From: Wei Wang MIME-Version: 1.0 References: <1532934837-5966-1-git-send-email-wei.w.wang@intel.com> <1532934837-5966-2-git-send-email-wei.w.wang@intel.com> <5B5EC604.4020301@intel.com> <87zhy8kgil.fsf@trasno.org> In-Reply-To: <87zhy8kgil.fsf@trasno.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/2] bitmap.h: add comments to BITMAP_LAST_WORD_MASK List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: quintela@redhat.com Cc: qemu-devel@nongnu.org, peterx@redhat.com, dgilbert@redhat.com, mst@redhat.com 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 0xffffffff. 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