Add utility class for unwrapping 16 bit sequence numbers

webrtc/modules/module_common_types_unittest.cc

Index: webrtc/modules/module_common_types_unittest.cc
diff --git a/webrtc/modules/module_common_types_unittest.cc b/webrtc/modules/module_common_types_unittest.cc
index 3e7f594166631fda651944638352170b813f1bff..bc0b7a1a5b2cb1517858afd2d25d8bb6211c5c12 100644
--- a/webrtc/modules/module_common_types_unittest.cc
+++ b/webrtc/modules/module_common_types_unittest.cc
@@ -122,4 +122,63 @@ TEST(ClampToInt16, TestCases) {
   EXPECT_EQ(-0x8000, ClampToInt16(-0x7FFFFFFF));
 }
 
+TEST(SequenceNumberUnwrapper, Limits) {
+  SequenceNumberUnwrapper unwrapper;
+
+  EXPECT_EQ(0, unwrapper.Unwrap(0));
+  EXPECT_EQ(0x8000, unwrapper.Unwrap(0x8000));
+  // Delta is exactly 0x8000 but current is lower than input, wrap backwards.
+  EXPECT_EQ(0x0, unwrapper.Unwrap(0x0000));
+
+  EXPECT_EQ(0x8000, unwrapper.Unwrap(0x8000));
+  EXPECT_EQ(0xFFFF, unwrapper.Unwrap(0xFFFF));
+  EXPECT_EQ(0x10000, unwrapper.Unwrap(0x0000));
+  EXPECT_EQ(0xFFFF, unwrapper.Unwrap(0xFFFF));
+  EXPECT_EQ(0x8000, unwrapper.Unwrap(0x8000));
+  EXPECT_EQ(0, unwrapper.Unwrap(0));
+
+  // Don't allow negative values.
+  EXPECT_EQ(0xFFFF, unwrapper.Unwrap(0xFFFF));
+}
+
+TEST(SequenceNumberUnwrapper, ForwardWraps) {
+  int64_t seq = 0;
+  SequenceNumberUnwrapper unwrapper;
+
+  const int kMaxIncrease = 0x8000 - 1;
+  const int kNumWraps = 4;
+  for (int i = 0; i < kNumWraps * 2; ++i) {
+    int64_t unwrapped = unwrapper.Unwrap(static_cast<uint16_t>(seq & 0xFFFF));
+    EXPECT_EQ(seq, unwrapped);
+    seq += kMaxIncrease;
+  }
+
+  unwrapper.UpdateLast(0);
+  for (int seq = 0; seq < kNumWraps * 0xFFFF; ++seq) {
+    int64_t unwrapped = unwrapper.Unwrap(static_cast<uint16_t>(seq & 0xFFFF));
+    EXPECT_EQ(seq, unwrapped);
+  }
+}
+
+TEST(SequenceNumberUnwrapper, BackwardWraps) {
+  SequenceNumberUnwrapper unwrapper;
+
+  const int kMaxDecrease = 0x8000 - 1;
+  const int kNumWraps = 4;
+  int64_t seq = kNumWraps * 2 * kMaxDecrease;
+  unwrapper.UpdateLast(seq);
+  for (int i = kNumWraps * 2; i >= 0; --i) {
+    int64_t unwrapped = unwrapper.Unwrap(static_cast<uint16_t>(seq & 0xFFFF));
+    EXPECT_EQ(seq, unwrapped);
+    seq -= kMaxDecrease;
+  }
+
+  seq = kNumWraps * 0xFFFF;
+  unwrapper.UpdateLast(seq);
+  for (; seq >= 0; --seq) {
+    int64_t unwrapped = unwrapper.Unwrap(static_cast<uint16_t>(seq & 0xFFFF));
+    EXPECT_EQ(seq, unwrapped);
+  }
+}
+
 }  // namespace webrtc