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