From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56566) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fk2oS-0005Sr-1F for qemu-devel@nongnu.org; Mon, 30 Jul 2018 03:41:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fk2oP-0001KT-AY for qemu-devel@nongnu.org; Mon, 30 Jul 2018 03:41:52 -0400 Received: from mga05.intel.com ([192.55.52.43]:40268) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fk2oP-0001K9-2Y for qemu-devel@nongnu.org; Mon, 30 Jul 2018 03:41:49 -0400 From: Wei Wang Date: Mon, 30 Jul 2018 15:13:56 +0800 Message-Id: <1532934837-5966-2-git-send-email-wei.w.wang@intel.com> In-Reply-To: <1532934837-5966-1-git-send-email-wei.w.wang@intel.com> References: <1532934837-5966-1-git-send-email-wei.w.wang@intel.com> Subject: [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: qemu-devel@nongnu.org, peterx@redhat.com, dgilbert@redhat.com, quintela@redhat.com Cc: mst@redhat.com 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) \ -- 2.7.4