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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 <chrono>
#include "platform/api/time.h"
namespace openscreen {
namespace cast {
// Tracks the jitter and drift between clocks, providing a smoothed offset.
// Internally, a Simple IIR filter is used to maintain a running average that
// moves at a rate based on the passage of time.
class ClockDriftSmoother {
// |time_constant| is the amount of time an impulse signal takes to decay by
// ~62.6%. Interpretation: If the value passed to several Update() calls is
// held constant for T seconds, then the running average will have moved
// towards the value by ~62.6% from where it started.
explicit ClockDriftSmoother(Clock::duration time_constant);
// Returns the current offset.
Clock::duration Current() const;
// Discard all history and reset to exactly |offset|, measured |now|.
void Reset(Clock::time_point now, Clock::duration offset);
// Update the current offset, which was measured |now|. The weighting that
// |measured_offset| will have on the running average is influenced by how
// much time has passed since the last call to this method (or Reset()).
// |now| should be monotonically non-decreasing over successive calls of this
// method.
void Update(Clock::time_point now, Clock::duration measured_offset);
// A time constant suitable for most use cases, where the clocks are expected
// to drift very little with respect to each other, and the jitter caused by
// clock imprecision is effectively canceled out.
static constexpr std::chrono::seconds kDefaultTimeConstant{30};
const std::chrono::duration<double, Clock::duration::period> time_constant_;
// The time at which |estimated_tick_offset_| was last updated.
Clock::time_point last_update_time_;
// The current estimated offset, as number of Clock::duration ticks.
double estimated_tick_offset_;
} // namespace cast
} // namespace openscreen