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* Copyright (c) 2011 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.
namespace rtc {
// This class can be used, for example, for smoothing the result of bandwidth
// estimation and packet loss estimation.
class ExpFilter {
static const float kValueUndefined;
explicit ExpFilter(float alpha, float max = kValueUndefined)
: max_(max) {
// Resets the filter to its initial state, and resets filter factor base to
// the given value |alpha|.
void Reset(float alpha);
// Applies the filter with a given exponent on the provided sample:
// y(k) = min(alpha_^ exp * y(k-1) + (1 - alpha_^ exp) * sample, max_).
float Apply(float exp, float sample);
// Returns current filtered value.
float filtered() const { return filtered_; }
// Changes the filter factor base to the given value |alpha|.
void UpdateBase(float alpha);
float alpha_; // Filter factor base.
float filtered_; // Current filter output.
const float max_;
} // namespace rtc