text: // Copyright 2014 The Chromium 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 "media/cast/common/clock_drift_smoother.h"
  
  #include <stdint.h>
  
  #include "base/logging.h"
  
  namespace media {
  namespace cast {
  
  ClockDriftSmoother::ClockDriftSmoother(base::TimeDelta time_constant)
      : time_constant_(time_constant),
        estimate_us_(0.0) {
    DCHECK(time_constant_ > base::TimeDelta());
  }
  
  ClockDriftSmoother::~ClockDriftSmoother() {}
  
  base::TimeDelta ClockDriftSmoother::Current() const {
    DCHECK(!last_update_time_.is_null());
    return base::TimeDelta::FromMicroseconds(static_cast<int64_t>(
        estimate_us_ + 0.5));  // Round to nearest microsecond.
  }
  
  void ClockDriftSmoother::Reset(base::TimeTicks now,
                                 base::TimeDelta measured_offset) {
    DCHECK(!now.is_null());
    last_update_time_ = now;
    estimate_us_ = static_cast<double>(measured_offset.InMicroseconds());
  }
  
  void ClockDriftSmoother::Update(base::TimeTicks now,
                                  base::TimeDelta measured_offset) {
    DCHECK(!now.is_null());
    if (last_update_time_.is_null()) {
      Reset(now, measured_offset);
    } else if (now < last_update_time_) {
      // |now| is not monotonically non-decreasing.
      NOTREACHED();
    } else {
      const double elapsed_us =
          static_cast<double>((now - last_update_time_).InMicroseconds());
      last_update_time_ = now;
      const double weight =
          elapsed_us / (elapsed_us + time_constant_.InMicroseconds());
      estimate_us_ = weight * measured_offset.InMicroseconds() +
          (1.0 - weight) * estimate_us_;
    }
  }
  
  // static
  base::TimeDelta ClockDriftSmoother::GetDefaultTimeConstant() {
    static const int kDefaultTimeConstantInSeconds = 30;
    return base::TimeDelta::FromSeconds(kDefaultTimeConstantInSeconds);
  }
  
  }  // namespace cast
  }  // namespace media
  