[Qemu-devel] [PATCH 1/2] bitmap.h: add comments to BITMAP_LAST_WORD_MASK

[Wei Wang <wei.w.wang@intel.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 <wei.w.wang@intel.com>
CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Peter Xu <peterx@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)                  \
-- 
2.7.4