1 /* 2 * Copyright (c) 2011 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11 #ifndef RTC_BASE_NUMERICS_EXP_FILTER_H_ 12 #define RTC_BASE_NUMERICS_EXP_FILTER_H_ 13 14 namespace rtc { 15 16 // This class can be used, for example, for smoothing the result of bandwidth 17 // estimation and packet loss estimation. 18 19 class ExpFilter { 20 public: 21 static const float kValueUndefined; 22 max_(max)23 explicit ExpFilter(float alpha, float max = kValueUndefined) : max_(max) { 24 Reset(alpha); 25 } 26 27 // Resets the filter to its initial state, and resets filter factor base to 28 // the given value |alpha|. 29 void Reset(float alpha); 30 31 // Applies the filter with a given exponent on the provided sample: 32 // y(k) = min(alpha_^ exp * y(k-1) + (1 - alpha_^ exp) * sample, max_). 33 float Apply(float exp, float sample); 34 35 // Returns current filtered value. filtered()36 float filtered() const { return filtered_; } 37 38 // Changes the filter factor base to the given value |alpha|. 39 void UpdateBase(float alpha); 40 41 private: 42 float alpha_; // Filter factor base. 43 float filtered_; // Current filter output. 44 const float max_; 45 }; 46 } // namespace rtc 47 48 #endif // RTC_BASE_NUMERICS_EXP_FILTER_H_ 49