Moved sequence number specific operations from mod_ops.h
to sequence_number_util.h

Also in this CL:
  - Implemented a MinDiff function which finds the smallest diff of two
    wrapping numbers.
  - Implemented comparators for sequence numbers.

BUG=
R=mflodman@webrtc.org, tommi@webrtc.org, torbjorng@webrtc.org

Review URL: https://codereview.webrtc.org/1814753002 .

Cr-Commit-Position: refs/heads/master@{#12083}
diff --git a/webrtc/modules/video_coding/sequence_number_util_unittest.cc b/webrtc/modules/video_coding/sequence_number_util_unittest.cc
new file mode 100644
index 0000000..8028efd
--- /dev/null
+++ b/webrtc/modules/video_coding/sequence_number_util_unittest.cc
@@ -0,0 +1,212 @@
+/*
+ *  Copyright (c) 2016 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 <set>
+
+#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/modules/video_coding/sequence_number_util.h"
+
+namespace webrtc {
+class TestSeqNumUtil : public ::testing::Test {
+ protected:
+  // Can't use std::numeric_limits<unsigned long>::max() since
+  // MSVC doesn't support constexpr.
+  static const unsigned long ulmax = ~0ul;  // NOLINT
+};
+
+TEST_F(TestSeqNumUtil, AheadOrAt) {
+  uint8_t x = 0;
+  uint8_t y = 0;
+  ASSERT_TRUE(AheadOrAt(x, y));
+  ++x;
+  ASSERT_TRUE(AheadOrAt(x, y));
+  ASSERT_FALSE(AheadOrAt(y, x));
+  for (int i = 0; i < 256; ++i) {
+    ASSERT_TRUE(AheadOrAt(x, y));
+    ++x;
+    ++y;
+  }
+
+  x = 128;
+  y = 0;
+  ASSERT_TRUE(AheadOrAt(x, y));
+  ASSERT_FALSE(AheadOrAt(y, x));
+
+  x = 129;
+  ASSERT_FALSE(AheadOrAt(x, y));
+  ASSERT_TRUE(AheadOrAt(y, x));
+  ASSERT_TRUE(AheadOrAt<uint16_t>(x, y));
+  ASSERT_FALSE(AheadOrAt<uint16_t>(y, x));
+}
+
+TEST_F(TestSeqNumUtil, AheadOrAtWithDivisor) {
+  ASSERT_TRUE((AheadOrAt<uint8_t, 11>(5, 0)));
+  ASSERT_FALSE((AheadOrAt<uint8_t, 11>(6, 0)));
+  ASSERT_FALSE((AheadOrAt<uint8_t, 11>(0, 5)));
+  ASSERT_TRUE((AheadOrAt<uint8_t, 11>(0, 6)));
+
+  ASSERT_TRUE((AheadOrAt<uint8_t, 10>(5, 0)));
+  ASSERT_FALSE((AheadOrAt<uint8_t, 10>(6, 0)));
+  ASSERT_FALSE((AheadOrAt<uint8_t, 10>(0, 5)));
+  ASSERT_TRUE((AheadOrAt<uint8_t, 10>(0, 6)));
+
+  const uint8_t D = 211;
+  uint8_t x = 0;
+  for (int i = 0; i < D; ++i) {
+    uint8_t next_x = Add<D>(x, 1);
+    ASSERT_TRUE((AheadOrAt<uint8_t, D>(i, i)));
+    ASSERT_TRUE((AheadOrAt<uint8_t, D>(next_x, i)));
+    ASSERT_FALSE((AheadOrAt<uint8_t, D>(i, next_x)));
+    x = next_x;
+  }
+}
+
+TEST_F(TestSeqNumUtil, AheadOf) {
+  uint8_t x = 0;
+  uint8_t y = 0;
+  ASSERT_FALSE(AheadOf(x, y));
+  ++x;
+  ASSERT_TRUE(AheadOf(x, y));
+  ASSERT_FALSE(AheadOf(y, x));
+  for (int i = 0; i < 256; ++i) {
+    ASSERT_TRUE(AheadOf(x, y));
+    ++x;
+    ++y;
+  }
+
+  x = 128;
+  y = 0;
+  for (int i = 0; i < 128; ++i) {
+    ASSERT_TRUE(AheadOf(x, y));
+    ASSERT_FALSE(AheadOf(y, x));
+    x++;
+    y++;
+  }
+
+  for (int i = 0; i < 128; ++i) {
+    ASSERT_FALSE(AheadOf(x, y));
+    ASSERT_TRUE(AheadOf(y, x));
+    x++;
+    y++;
+  }
+
+  x = 129;
+  y = 0;
+  ASSERT_FALSE(AheadOf(x, y));
+  ASSERT_TRUE(AheadOf(y, x));
+  ASSERT_TRUE(AheadOf<uint16_t>(x, y));
+  ASSERT_FALSE(AheadOf<uint16_t>(y, x));
+}
+
+TEST_F(TestSeqNumUtil, AheadOfWithDivisor) {
+  ASSERT_TRUE((AheadOf<uint8_t, 11>(5, 0)));
+  ASSERT_FALSE((AheadOf<uint8_t, 11>(6, 0)));
+  ASSERT_FALSE((AheadOf<uint8_t, 11>(0, 5)));
+  ASSERT_TRUE((AheadOf<uint8_t, 11>(0, 6)));
+
+  ASSERT_TRUE((AheadOf<uint8_t, 10>(5, 0)));
+  ASSERT_FALSE((AheadOf<uint8_t, 10>(6, 0)));
+  ASSERT_FALSE((AheadOf<uint8_t, 10>(0, 5)));
+  ASSERT_TRUE((AheadOf<uint8_t, 10>(0, 6)));
+
+  const uint8_t D = 211;
+  uint8_t x = 0;
+  for (int i = 0; i < D; ++i) {
+    uint8_t next_x = Add<D>(x, 1);
+    ASSERT_FALSE((AheadOf<uint8_t, D>(i, i)));
+    ASSERT_TRUE((AheadOf<uint8_t, D>(next_x, i)));
+    ASSERT_FALSE((AheadOf<uint8_t, D>(i, next_x)));
+    x = next_x;
+  }
+}
+
+TEST_F(TestSeqNumUtil, ForwardDiffWithDivisor) {
+  const uint8_t kDivisor = 211;
+
+  for (uint8_t i = 0; i < kDivisor - 1; ++i) {
+    ASSERT_EQ(0, (ForwardDiff<uint8_t, kDivisor>(i, i)));
+    ASSERT_EQ(1, (ForwardDiff<uint8_t, kDivisor>(i, i + 1)));
+    ASSERT_EQ(kDivisor - 1, (ForwardDiff<uint8_t, kDivisor>(i + 1, i)));
+  }
+
+  for (uint8_t i = 1; i < kDivisor; ++i) {
+    ASSERT_EQ(i, (ForwardDiff<uint8_t, kDivisor>(0, i)));
+    ASSERT_EQ(kDivisor - i, (ForwardDiff<uint8_t, kDivisor>(i, 0)));
+  }
+}
+
+TEST_F(TestSeqNumUtil, ReverseDiffWithDivisor) {
+  const uint8_t kDivisor = 241;
+
+  for (uint8_t i = 0; i < kDivisor - 1; ++i) {
+    ASSERT_EQ(0, (ReverseDiff<uint8_t, kDivisor>(i, i)));
+    ASSERT_EQ(kDivisor - 1, (ReverseDiff<uint8_t, kDivisor>(i, i + 1)));
+    ASSERT_EQ(1, (ReverseDiff<uint8_t, kDivisor>(i + 1, i)));
+  }
+
+  for (uint8_t i = 1; i < kDivisor; ++i) {
+    ASSERT_EQ(kDivisor - i, (ReverseDiff<uint8_t, kDivisor>(0, i)));
+    ASSERT_EQ(i, (ReverseDiff<uint8_t, kDivisor>(i, 0)));
+  }
+}
+
+TEST_F(TestSeqNumUtil, SeqNumComparator) {
+  std::set<uint8_t, AscendingSeqNumComp<uint8_t>> seq_nums_asc;
+  std::set<uint8_t, DescendingSeqNumComp<uint8_t>> seq_nums_desc;
+
+  uint8_t x = 0;
+  for (int i = 0; i < 128; ++i) {
+    seq_nums_asc.insert(x);
+    seq_nums_desc.insert(x);
+    ASSERT_EQ(x, *seq_nums_asc.begin());
+    ASSERT_EQ(x, *seq_nums_desc.rbegin());
+    ++x;
+  }
+
+  seq_nums_asc.clear();
+  seq_nums_desc.clear();
+  x = 199;
+  for (int i = 0; i < 128; ++i) {
+    seq_nums_asc.insert(x);
+    seq_nums_desc.insert(x);
+    ASSERT_EQ(x, *seq_nums_asc.begin());
+    ASSERT_EQ(x, *seq_nums_desc.rbegin());
+    ++x;
+  }
+}
+
+TEST_F(TestSeqNumUtil, SeqNumComparatorWithDivisor) {
+  const uint8_t D = 223;
+
+  std::set<uint8_t, AscendingSeqNumComp<uint8_t, D>> seq_nums_asc;
+  std::set<uint8_t, DescendingSeqNumComp<uint8_t, D>> seq_nums_desc;
+
+  uint8_t x = 0;
+  for (int i = 0; i < D / 2; ++i) {
+    seq_nums_asc.insert(x);
+    seq_nums_desc.insert(x);
+    ASSERT_EQ(x, *seq_nums_asc.begin());
+    ASSERT_EQ(x, *seq_nums_desc.rbegin());
+    x = Add<D>(x, 1);
+  }
+
+  seq_nums_asc.clear();
+  seq_nums_desc.clear();
+  x = 200;
+  for (int i = 0; i < D / 2; ++i) {
+    seq_nums_asc.insert(x);
+    seq_nums_desc.insert(x);
+    ASSERT_EQ(x, *seq_nums_asc.begin());
+    ASSERT_EQ(x, *seq_nums_desc.rbegin());
+    x = Add<D>(x, 1);
+  }
+}
+
+}  // namespace webrtc