1 files changed, 146 insertions, 0 deletions
diff --git a/dom/media/doctor/test/gtest/TestRollingNumber.cpp b/dom/media/doctor/test/gtest/TestRollingNumber.cpp
new file mode 100644
index 0000000000..cce06ae9ba
--- /dev/null
+++ b/dom/media/doctor/test/gtest/TestRollingNumber.cpp
@@ -0,0 +1,146 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RollingNumber.h"
+
+#include "mozilla/Assertions.h"
+
+#include <cstdint>
+#include <gtest/gtest.h>
+#include <type_traits>
+
+using RN8 = mozilla::RollingNumber<uint8_t>;
+
+TEST(RollingNumber, Value)
+{
+  // Value type should reflect template argument.
+  static_assert(std::is_same_v<RN8::ValueType, uint8_t>);
+
+  // Default init to 0.
+  const RN8 n;
+  // Access through Value().
+  EXPECT_EQ(0, n.Value());
+
+  // Conversion constructor.
+  RN8 n42{42};
+  EXPECT_EQ(42, n42.Value());
+
+  // Copy Constructor.
+  RN8 n42Copied{n42};
+  EXPECT_EQ(42, n42Copied.Value());
+
+  // Assignment construction.
+  RN8 n42Assigned = n42;
+  EXPECT_EQ(42, n42Assigned.Value());
+
+  // Assignment.
+  n42 = n;
+  EXPECT_EQ(0, n42.Value());
+}
+
+TEST(RollingNumber, Operations)
+{
+  RN8 n;
+  EXPECT_EQ(0, n.Value());
+
+  RN8 nPreInc = ++n;
+  EXPECT_EQ(1, n.Value());
+  EXPECT_EQ(1, nPreInc.Value());
+
+  RN8 nPostInc = n++;
+  EXPECT_EQ(2, n.Value());
+  EXPECT_EQ(1, nPostInc.Value());
+
+  RN8 nPreDec = --n;
+  EXPECT_EQ(1, n.Value());
+  EXPECT_EQ(1, nPreDec.Value());
+
+  RN8 nPostDec = n--;
+  EXPECT_EQ(0, n.Value());
+  EXPECT_EQ(1, nPostDec.Value());
+
+  RN8 nPlus = n + 10;
+  EXPECT_EQ(0, n.Value());
+  EXPECT_EQ(10, nPlus.Value());
+
+  n += 20;
+  EXPECT_EQ(20, n.Value());
+
+  RN8 nMinus = n - 2;
+  EXPECT_EQ(20, n.Value());
+  EXPECT_EQ(18, nMinus.Value());
+
+  n -= 5;
+  EXPECT_EQ(15, n.Value());
+
+  uint8_t diff = nMinus - n;
+  EXPECT_EQ(3, diff);
+
+  // Overflows.
+  n = RN8(0);
+  EXPECT_EQ(0, n.Value());
+  n--;
+  EXPECT_EQ(255, n.Value());
+  n++;
+  EXPECT_EQ(0, n.Value());
+  n -= 10;
+  EXPECT_EQ(246, n.Value());
+  n += 20;
+  EXPECT_EQ(10, n.Value());
+}
+
+TEST(RollingNumber, Comparisons)
+{
+  uint8_t i = 0;
+  do {
+    RN8 n{i};
+    EXPECT_EQ(i, n.Value());
+    EXPECT_TRUE(n == n);
+    EXPECT_FALSE(n != n);
+    EXPECT_FALSE(n < n);
+    EXPECT_TRUE(n <= n);
+    EXPECT_FALSE(n > n);
+    EXPECT_TRUE(n >= n);
+
+    RN8 same = n;
+    EXPECT_TRUE(n == same);
+    EXPECT_FALSE(n != same);
+    EXPECT_FALSE(n < same);
+    EXPECT_TRUE(n <= same);
+    EXPECT_FALSE(n > same);
+    EXPECT_TRUE(n >= same);
+
+#ifdef DEBUG
+    // In debug builds, we are only allowed a quarter of the type range.
+    const uint8_t maxDiff = 255 / 4;
+#else
+    // In non-debug builds, we can go half-way up or down the type range, and
+    // still conserve the expected ordering.
+    const uint8_t maxDiff = 255 / 2;
+#endif
+    for (uint8_t add = 1; add <= maxDiff; ++add) {
+      RN8 bigger = n + add;
+      EXPECT_FALSE(n == bigger);
+      EXPECT_TRUE(n != bigger);
+      EXPECT_TRUE(n < bigger);
+      EXPECT_TRUE(n <= bigger);
+      EXPECT_FALSE(n > bigger);
+      EXPECT_FALSE(n >= bigger);
+    }
+
+    for (uint8_t sub = 1; sub <= maxDiff; ++sub) {
+      RN8 smaller = n - sub;
+      EXPECT_FALSE(n == smaller);
+      EXPECT_TRUE(n != smaller);
+      EXPECT_FALSE(n < smaller);
+      EXPECT_FALSE(n <= smaller);
+      EXPECT_TRUE(n > smaller);
+      EXPECT_TRUE(n >= smaller);
+    }
+
+    ++i;
+  } while (i != 0);
+}