[FFmpeg-cvslog] libavutil: Use an intermediate variable in AV_COPY*U

[Martin Storsjö]

ffmpeg | branch: master | Martin Storsjö <martin at martin.st> | Thu Jul 28 14:30:25 2016 +0300| [014773b66bdff4de24f384066d1a85d2a5bb6774] | committer: Martin Storsjö

libavutil: Use an intermediate variable in AV_COPY*U

If AV_RN and AV_WN are macros with multiple individual reads and
writes, the previous version of the AV_COPYU macro would fail if
the reads and writes overlap.

This should not be any less efficient in any case, given a
sensibly optimizing compiler.

Signed-off-by: Martin Storsjö <martin at martin.st>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=014773b66bdff4de24f384066d1a85d2a5bb6774
---

 libavutil/intreadwrite.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libavutil/intreadwrite.h b/libavutil/intreadwrite.h
index f77fd60..cdf1ef4 100644
--- a/libavutil/intreadwrite.h
+++ b/libavutil/intreadwrite.h
@@ -467,7 +467,11 @@ union unaligned_16 { uint16_t l; } __attribute__((packed)) av_alias;
  * memory locations.
  */
 
-#define AV_COPYU(n, d, s) AV_WN##n(d, AV_RN##n(s));
+#define AV_COPYU(n, d, s)                                       \
+    do {                                                        \
+        uint##n##_t val = AV_RN##n(s);                          \
+        AV_WN##n(d, val);                                       \
+    } while (0)
 
 #ifndef AV_COPY16U
 #   define AV_COPY16U(d, s) AV_COPYU(16, d, s)