Adds a modified copy of talk/base to webrtc/base. It is the first step in migrating talk/base to webrtc/base.

BUG=N/A
R=andrew@webrtc.org, wu@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/12199004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6107 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/base/ratetracker.cc

@@ -0,0 +1,63 @@
+/*
+ *  Copyright 2004 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 "webrtc/base/ratetracker.h"
+#include "webrtc/base/timeutils.h"
+
+namespace rtc {
+
+RateTracker::RateTracker()
+    : total_units_(0), units_second_(0),
+      last_units_second_time_(static_cast<uint32>(-1)),
+      last_units_second_calc_(0) {
+}
+
+size_t RateTracker::total_units() const {
+  return total_units_;
+}
+
+size_t RateTracker::units_second() {
+  // Snapshot units / second calculator. Determine how many seconds have
+  // elapsed since our last reference point. If over 1 second, establish
+  // a new reference point that is an integer number of seconds since the
+  // last one, and compute the units over that interval.
+  uint32 current_time = Time();
+  if (last_units_second_time_ != static_cast<uint32>(-1)) {
+    int delta = rtc::TimeDiff(current_time, last_units_second_time_);
+    if (delta >= 1000) {
+      int fraction_time = delta % 1000;
+      int seconds = delta / 1000;
+      int fraction_units =
+          static_cast<int>(total_units_ - last_units_second_calc_) *
+              fraction_time / delta;
+      // Compute "units received during the interval" / "seconds in interval"
+      units_second_ =
+          (total_units_ - last_units_second_calc_ - fraction_units) / seconds;
+      last_units_second_time_ = current_time - fraction_time;
+      last_units_second_calc_ = total_units_ - fraction_units;
+    }
+  }
+  if (last_units_second_time_ == static_cast<uint32>(-1)) {
+    last_units_second_time_ = current_time;
+    last_units_second_calc_ = total_units_;
+  }
+
+  return units_second_;
+}
+
+void RateTracker::Update(size_t units) {
+  total_units_ += units;
+}
+
+uint32 RateTracker::Time() const {
+  return rtc::Time();
+}
+
+}  // namespace rtc