[Qemu-devel] [PATCH v9 1/8] bitmap: fix bitmap_count_one

[Wei Wang <wei.w.wang@intel.com>]

BITMAP_LAST_WORD_MASK(nbits) returns 0xffffffff when "nbits=0", which
makes bitmap_count_one fail to handle the "nbits=0" case. It appears to be
preferred to remain BITMAP_LAST_WORD_MASK identical to the kernel
implementation that it is ported from.

So this patch fixes bitmap_count_one to handle the nbits=0 case.

Inital Discussion Link:
https://www.mail-archive.com/qemu-devel@nongnu.org/msg554316.html
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
CC: Peter Xu <peterx@redhat.com>
---
 include/qemu/bitmap.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h
index 509eedd..679f1bd 100644
--- a/include/qemu/bitmap.h
+++ b/include/qemu/bitmap.h
@@ -221,6 +221,10 @@ static inline int bitmap_intersects(const unsigned long *src1,
 
 static inline long bitmap_count_one(const unsigned long *bitmap, long nbits)
 {
+    if (unlikely(!nbits)) {
+        return 0;
+    }
+
     if (small_nbits(nbits)) {
         return ctpopl(*bitmap & BITMAP_LAST_WORD_MASK(nbits));
     } else {
-- 
1.8.3.1