[Qemu-devel] [PATCH v3 1/9] bt-sdp: fix broken uuids power-of-2 calculation

[Stefan Hajnoczi <stefanha@redhat.com>]

The binary search in sdp_uuid_match() only works when the number of
elements to search is a power of two.

  lo = record->uuid;
  hi = record->uuids;
  while (hi >>= 1)
      if (lo[hi] <= val)
          lo += hi;

  return *lo == val;

I noticed that the record->uuids calculation in
sdp_service_record_build() was suspect:

  record->uuids = 1 << ffs(record->uuids - 1);

Unlike most ffs(val) - 1 users, the expression is ffs(val - 1)!

Actually ffs() is the wrong function to use for power-of-2.  Use
pow2ceil() to achieve the correct effect.  Now the record->uuid[] array
is sized correctly and the binary search in sdp_uuid_match() should
work.

I'm not sure how to run/test this code.

Cc: Andrzej Zaborowski <balrog@zabor.org>
Cc: qemu-stable@nongnu.org
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/bt/sdp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/bt/sdp.c b/hw/bt/sdp.c
index 218e075..c903747 100644
--- a/hw/bt/sdp.c
+++ b/hw/bt/sdp.c
@@ -707,7 +707,7 @@ static void sdp_service_record_build(struct sdp_service_record_s *record,
         len += sdp_attr_max_size(&def->attributes[record->attributes ++].data,
                         &record->uuids);
     }
-    record->uuids = 1 << ffs(record->uuids - 1);
+    record->uuids = pow2ceil(record->uuids);
     record->attribute_list =
             g_malloc0(record->attributes * sizeof(*record->attribute_list));
     record->uuid =
-- 
2.1.0