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/check.h"
  #include "base/notreached.h"
  #include "base/numerics/safe_conversions.h"
  
  namespace media {
  namespace cast {
  
  ClockDriftSmoother::ClockDriftSmoother(base::TimeDelta time_constant)
      : time_constant_(time_constant),
        estimate_us_(0.0) {
    DCHECK(time_constant_.is_positive());
  }
  
  ClockDriftSmoother::~ClockDriftSmoother() = default;
  
  base::TimeDelta ClockDriftSmoother::Current() const {
    DCHECK(!last_update_time_.is_null());
    return base::Microseconds(base::ClampRound<int64_t>(estimate_us_));
  }
  
  void ClockDriftSmoother::Reset(base::TimeTicks now,
                                 base::TimeDelta measured_offset) {
    DCHECK(!now.is_null());
    last_update_time_ = now;
    estimate_us_ = measured_offset.InMicrosecondsF();
  }
  
  void ClockDriftSmoother::Update(base::TimeTicks now,
                                  base::TimeDelta measured_offset) {
    DCHECK(!now.is_null());
    if (last_update_time_.is_null()) {
      Reset(now, measured_offset);
      return;
    }
  
    DCHECK_GE(now, last_update_time_);  // |now| is monotonically non-decreasing.
    const base::TimeDelta elapsed = now - last_update_time_;
    last_update_time_ = now;
    const double weight = elapsed / (elapsed + time_constant_);
    estimate_us_ = weight * measured_offset.InMicrosecondsF() +
                   (1.0 - weight) * estimate_us_;
  }
  
  // static
  base::TimeDelta ClockDriftSmoother::GetDefaultTimeConstant() {
    return base::Seconds(30);
  }
  
  }  // namespace cast
  }  // namespace media
  