Add metric for number of packets discarded by JB due to not being decodable

Also fixes a couple of bugs related to sequence number wrap found while
testing.

BUG=
TEST=

Review URL: http://webrtc-codereview.appspot.com/218001

git-svn-id: http://webrtc.googlecode.com/svn/trunk@732 4adac7df-926f-26a2-2b94-8c16560cd09d

src/modules/video_coding/main/source/jitter_buffer_common.cc

@@ -0,0 +1,60 @@
+/*
+ *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "jitter_buffer_common.h"
+
+#include <cstdlib>
+
+namespace webrtc {
+
+WebRtc_UWord32 LatestTimestamp(WebRtc_UWord32 timestamp1,
+                               WebRtc_UWord32 timestamp2,
+                               bool* has_wrapped) {
+  bool wrap = (timestamp2 < 0x0000ffff && timestamp1 > 0xffff0000) ||
+      (timestamp2 > 0xffff0000 && timestamp1 < 0x0000ffff);
+  if (has_wrapped != NULL)
+    *has_wrapped = wrap;
+  if (timestamp1 > timestamp2 && !wrap)
+      return timestamp1;
+  else if (timestamp1 <= timestamp2 && !wrap)
+      return timestamp2;
+  else if (timestamp1 < timestamp2 && wrap)
+      return timestamp1;
+  else
+      return timestamp2;
+}
+
+WebRtc_Word32 LatestSequenceNumber(WebRtc_Word32 seq_num1,
+                                   WebRtc_Word32 seq_num2,
+                                   bool* has_wrapped) {
+  if (seq_num1 < 0 && seq_num2 < 0)
+    return -1;
+  else if (seq_num1 < 0)
+    return seq_num2;
+  else if (seq_num2 < 0)
+    return seq_num1;
+
+  bool wrap = (seq_num1 < 0x00ff && seq_num2 > 0xff00) ||
+          (seq_num1 > 0xff00 && seq_num2 < 0x00ff);
+
+  if (has_wrapped != NULL)
+    *has_wrapped = wrap;
+
+  if (seq_num2 > seq_num1 && !wrap)
+    return seq_num2;
+  else if (seq_num2 <= seq_num1 && !wrap)
+    return seq_num1;
+  else if (seq_num2 < seq_num1 && wrap)
+    return seq_num2;
+  else
+    return seq_num1;
+}
+
+}  // namespace webrtc