Refactor the ring buffer in GCTracer.

test/unittests/heap/gc-tracer-unittest.cc

+// Copyright 2014 the V8 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.
+
+#include <cmath>
+#include <limits>
+
+#include "src/heap/gc-tracer.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace v8 {
+namespace internal {
+
+TEST(GCTracer, AverageSpeed) {
+  RingBuffer<BytesAndDuration> buffer;
+  EXPECT_EQ(100 / 2,
+            GCTracer::AverageSpeed(buffer, MakeBytesAndDuration(100, 2), 0));
+  buffer.Push(MakeBytesAndDuration(100, 8));
+  EXPECT_EQ(100 / 2,
+            GCTracer::AverageSpeed(buffer, MakeBytesAndDuration(100, 2), 2));
+  EXPECT_EQ(200 / 10,
+            GCTracer::AverageSpeed(buffer, MakeBytesAndDuration(100, 2), 3));
+  const int max_speed = 1024 * MB;
+  buffer.Reset();
+  buffer.Push(MakeBytesAndDuration(max_speed, 0.5));
+  EXPECT_EQ(max_speed,
+            GCTracer::AverageSpeed(buffer, MakeBytesAndDuration(0, 0), 1));
+  const int min_speed = 1;
+  buffer.Reset();
+  buffer.Push(MakeBytesAndDuration(1, 10000));
+  EXPECT_EQ(min_speed,
+            GCTracer::AverageSpeed(buffer, MakeBytesAndDuration(0, 0), 1));
+  buffer.Reset();
+  int sum = 0;
+  for (int i = 0; i < buffer.kSize; i++) {
+    sum += i + 1;
+    buffer.Push(MakeBytesAndDuration(i + 1, 1));
+  }
+  EXPECT_EQ(
+      static_cast<int>(sum * 1.0 / buffer.kSize + 0.5),
+      GCTracer::AverageSpeed(buffer, MakeBytesAndDuration(0, 0), buffer.kSize));
+  buffer.Push(MakeBytesAndDuration(100, 1));
+  EXPECT_EQ(
+      static_cast<int>((sum * 1.0 - 1 + 100) / buffer.kSize + 0.5),
+      GCTracer::AverageSpeed(buffer, MakeBytesAndDuration(0, 0), buffer.kSize));
+}
+
+}  // namespace internal
+}  // namespace v8