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// 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 "cast/streaming/clock_drift_smoother.h"
#include <cmath>
#include "util/osp_logging.h"
#include "util/saturate_cast.h"
namespace openscreen {
namespace cast {
namespace {
constexpr Clock::time_point kNullTime = Clock::time_point::min();
}
ClockDriftSmoother::ClockDriftSmoother(Clock::duration time_constant)
: time_constant_(time_constant),
last_update_time_(kNullTime),
estimated_tick_offset_(0.0) {
OSP_DCHECK(time_constant_ > decltype(time_constant_)::zero());
}
ClockDriftSmoother::~ClockDriftSmoother() = default;
Clock::duration ClockDriftSmoother::Current() const {
OSP_DCHECK(last_update_time_ != kNullTime);
return Clock::duration(
rounded_saturate_cast<Clock::duration::rep>(estimated_tick_offset_));
}
void ClockDriftSmoother::Reset(Clock::time_point now,
Clock::duration measured_offset) {
OSP_DCHECK(now != kNullTime);
last_update_time_ = now;
estimated_tick_offset_ = static_cast<double>(measured_offset.count());
}
void ClockDriftSmoother::Update(Clock::time_point now,
Clock::duration measured_offset) {
OSP_DCHECK(now != kNullTime);
if (last_update_time_ == kNullTime) {
Reset(now, measured_offset);
} else if (now < last_update_time_) {
// |now| is not monotonically non-decreasing.
OSP_NOTREACHED();
} else {
const double elapsed_ticks =
static_cast<double>((now - last_update_time_).count());
last_update_time_ = now;
// Compute a weighted-average between the last estimate and
// |measured_offset|. The more time that has elasped since the last call to
// Update(), the more-heavily |measured_offset| will be weighed.
const double weight =
elapsed_ticks / (elapsed_ticks + time_constant_.count());
estimated_tick_offset_ = weight * measured_offset.count() +
(1.0 - weight) * estimated_tick_offset_;
}
}
// static
constexpr std::chrono::seconds ClockDriftSmoother::kDefaultTimeConstant;
} // namespace cast
} // namespace openscreen
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