commit df9e6aaf716279baf0e27b99acf10005924245ed
author Robert Shih <robertshih@google.com> Tue Dec 29 11:13:53 2015 -0800
committer Robert Shih <robertshih@google.com> Tue Dec 29 11:39:02 2015 -0800
tree 4d7e398d89f5a6a796f4078362701b6db7f61bff
parent 436ae0b8babc9c37f17a61dc6153f26eaa05e343

ARTPSource: avoid over/underflow in seq # recovery

Bug: 25801317
Change-Id: Id9a5ad2d6c27f64b502c78f06174b29edb486134

media/libstagefright/rtsp/ARTPSource.cpp

diff --git a/media/libstagefright/rtsp/ARTPSource.cpp b/media/libstagefright/rtsp/ARTPSource.cpp
index d7c3bd6..576a0a4 100644
--- a/media/libstagefright/rtsp/ARTPSource.cpp
+++ b/media/libstagefright/rtsp/ARTPSource.cpp
@@ -116,8 +116,15 @@
     // to the highest sequence number (extended to 32 bits) received so far.
 
     uint32_t seq1 = seqNum | (mHighestSeqNumber & 0xffff0000);
-    uint32_t seq2 = seqNum | ((mHighestSeqNumber & 0xffff0000) + 0x10000);
-    uint32_t seq3 = seqNum | ((mHighestSeqNumber & 0xffff0000) - 0x10000);
+
+    // non-overflowing version of:
+    // uint32_t seq2 = seqNum | ((mHighestSeqNumber & 0xffff0000) + 0x10000);
+    uint32_t seq2 = seqNum | (((mHighestSeqNumber >> 16) + 1) << 16);
+
+    // non-underflowing version of:
+    // uint32_t seq2 = seqNum | ((mHighestSeqNumber & 0xffff0000) - 0x10000);
+    uint32_t seq3 = seqNum | ((((mHighestSeqNumber >> 16) | 0x10000) - 1) << 16);
+
     uint32_t diff1 = AbsDiff(seq1, mHighestSeqNumber);
     uint32_t diff2 = AbsDiff(seq2, mHighestSeqNumber);
     uint32_t diff3 = AbsDiff(seq3, mHighestSeqNumber);