dcsctp: Added common utilities

These are quite generic utilities that are used by multiple modules
within dcSCTP. Some would be good to have in rtc_base and are simple
replicas of utilities available in abseil.

Bug: webrtc:12614
Change-Id: I9914286ced7317a34628a71697da9149d6d19d38
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/213190
Reviewed-by: Tommi <tommi@webrtc.org>
Commit-Queue: Victor Boivie <boivie@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33609}

net/dcsctp/common/sequence_numbers_test.cc

diff --git a/net/dcsctp/common/sequence_numbers_test.cc b/net/dcsctp/common/sequence_numbers_test.cc
new file mode 100644
index 0000000..f7ecd9b
--- /dev/null
+++ b/net/dcsctp/common/sequence_numbers_test.cc
@@ -0,0 +1,186 @@
+/*
+ *  Copyright (c) 2021 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 "net/dcsctp/common/sequence_numbers.h"
+
+#include "test/gmock.h"
+
+namespace dcsctp {
+namespace {
+
+using TestSequence = UnwrappedSequenceNumber<uint16_t>;
+
+TEST(SequenceNumbersTest, SimpleUnwrapping) {
+  TestSequence::Unwrapper unwrapper;
+
+  TestSequence s0 = unwrapper.Unwrap(0);
+  TestSequence s1 = unwrapper.Unwrap(1);
+  TestSequence s2 = unwrapper.Unwrap(2);
+  TestSequence s3 = unwrapper.Unwrap(3);
+
+  EXPECT_LT(s0, s1);
+  EXPECT_LT(s0, s2);
+  EXPECT_LT(s0, s3);
+  EXPECT_LT(s1, s2);
+  EXPECT_LT(s1, s3);
+  EXPECT_LT(s2, s3);
+
+  EXPECT_EQ(s1.Difference(s0), 1);
+  EXPECT_EQ(s2.Difference(s0), 2);
+  EXPECT_EQ(s3.Difference(s0), 3);
+
+  EXPECT_GT(s1, s0);
+  EXPECT_GT(s2, s0);
+  EXPECT_GT(s3, s0);
+  EXPECT_GT(s2, s1);
+  EXPECT_GT(s3, s1);
+  EXPECT_GT(s3, s2);
+
+  s0.Increment();
+  EXPECT_EQ(s0, s1);
+  s1.Increment();
+  EXPECT_EQ(s1, s2);
+  s2.Increment();
+  EXPECT_EQ(s2, s3);
+
+  EXPECT_EQ(s0.AddTo(2), s3);
+}
+
+TEST(SequenceNumbersTest, MidValueUnwrapping) {
+  TestSequence::Unwrapper unwrapper;
+
+  TestSequence s0 = unwrapper.Unwrap(0x7FFE);
+  TestSequence s1 = unwrapper.Unwrap(0x7FFF);
+  TestSequence s2 = unwrapper.Unwrap(0x8000);
+  TestSequence s3 = unwrapper.Unwrap(0x8001);
+
+  EXPECT_LT(s0, s1);
+  EXPECT_LT(s0, s2);
+  EXPECT_LT(s0, s3);
+  EXPECT_LT(s1, s2);
+  EXPECT_LT(s1, s3);
+  EXPECT_LT(s2, s3);
+
+  EXPECT_EQ(s1.Difference(s0), 1);
+  EXPECT_EQ(s2.Difference(s0), 2);
+  EXPECT_EQ(s3.Difference(s0), 3);
+
+  EXPECT_GT(s1, s0);
+  EXPECT_GT(s2, s0);
+  EXPECT_GT(s3, s0);
+  EXPECT_GT(s2, s1);
+  EXPECT_GT(s3, s1);
+  EXPECT_GT(s3, s2);
+
+  s0.Increment();
+  EXPECT_EQ(s0, s1);
+  s1.Increment();
+  EXPECT_EQ(s1, s2);
+  s2.Increment();
+  EXPECT_EQ(s2, s3);
+
+  EXPECT_EQ(s0.AddTo(2), s3);
+}
+
+TEST(SequenceNumbersTest, WrappedUnwrapping) {
+  TestSequence::Unwrapper unwrapper;
+
+  TestSequence s0 = unwrapper.Unwrap(0xFFFE);
+  TestSequence s1 = unwrapper.Unwrap(0xFFFF);
+  TestSequence s2 = unwrapper.Unwrap(0x0000);
+  TestSequence s3 = unwrapper.Unwrap(0x0001);
+
+  EXPECT_LT(s0, s1);
+  EXPECT_LT(s0, s2);
+  EXPECT_LT(s0, s3);
+  EXPECT_LT(s1, s2);
+  EXPECT_LT(s1, s3);
+  EXPECT_LT(s2, s3);
+
+  EXPECT_EQ(s1.Difference(s0), 1);
+  EXPECT_EQ(s2.Difference(s0), 2);
+  EXPECT_EQ(s3.Difference(s0), 3);
+
+  EXPECT_GT(s1, s0);
+  EXPECT_GT(s2, s0);
+  EXPECT_GT(s3, s0);
+  EXPECT_GT(s2, s1);
+  EXPECT_GT(s3, s1);
+  EXPECT_GT(s3, s2);
+
+  s0.Increment();
+  EXPECT_EQ(s0, s1);
+  s1.Increment();
+  EXPECT_EQ(s1, s2);
+  s2.Increment();
+  EXPECT_EQ(s2, s3);
+
+  EXPECT_EQ(s0.AddTo(2), s3);
+}
+
+TEST(SequenceNumbersTest, WrapAroundAFewTimes) {
+  TestSequence::Unwrapper unwrapper;
+
+  TestSequence s0 = unwrapper.Unwrap(0);
+  TestSequence prev = s0;
+
+  for (uint32_t i = 1; i < 65536 * 3; i++) {
+    uint16_t wrapped = static_cast<uint16_t>(i);
+    TestSequence si = unwrapper.Unwrap(wrapped);
+
+    EXPECT_LT(s0, si);
+    EXPECT_LT(prev, si);
+    prev = si;
+  }
+}
+
+TEST(SequenceNumbersTest, IncrementIsSameAsWrapped) {
+  TestSequence::Unwrapper unwrapper;
+
+  TestSequence s0 = unwrapper.Unwrap(0);
+
+  for (uint32_t i = 1; i < 65536 * 2; i++) {
+    uint16_t wrapped = static_cast<uint16_t>(i);
+    TestSequence si = unwrapper.Unwrap(wrapped);
+
+    s0.Increment();
+    EXPECT_EQ(s0, si);
+  }
+}
+
+TEST(SequenceNumbersTest, UnwrappingLargerNumberIsAlwaysLarger) {
+  TestSequence::Unwrapper unwrapper;
+
+  for (uint32_t i = 1; i < 65536 * 2; i++) {
+    uint16_t wrapped = static_cast<uint16_t>(i);
+    TestSequence si = unwrapper.Unwrap(wrapped);
+
+    EXPECT_GT(unwrapper.Unwrap(wrapped + 1), si);
+    EXPECT_GT(unwrapper.Unwrap(wrapped + 5), si);
+    EXPECT_GT(unwrapper.Unwrap(wrapped + 10), si);
+    EXPECT_GT(unwrapper.Unwrap(wrapped + 100), si);
+  }
+}
+
+TEST(SequenceNumbersTest, UnwrappingSmallerNumberIsAlwaysSmaller) {
+  TestSequence::Unwrapper unwrapper;
+
+  for (uint32_t i = 1; i < 65536 * 2; i++) {
+    uint16_t wrapped = static_cast<uint16_t>(i);
+    TestSequence si = unwrapper.Unwrap(wrapped);
+
+    EXPECT_LT(unwrapper.Unwrap(wrapped - 1), si);
+    EXPECT_LT(unwrapper.Unwrap(wrapped - 5), si);
+    EXPECT_LT(unwrapper.Unwrap(wrapped - 10), si);
+    EXPECT_LT(unwrapper.Unwrap(wrapped - 100), si);
+  }
+}
+
+}  // namespace
+}  // namespace dcsctp