1 /*
2  * Copyright (C) 2011 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef ANDROID_FILTERFW_CORE_STATISTICS_H
18 #define ANDROID_FILTERFW_CORE_STATISTICS_H
19 
20 namespace android {
21 namespace filterfw {
22 
23 // An incrementally-constructed Normal distribution.
24 class IncrementalGaussian {
25  public:
26   IncrementalGaussian();
27 
28   void Add(float value);
29 
NumSamples()30   float NumSamples() const { return n_; }
Mean()31   float Mean() const { return mean_; }
Var()32   float Var() const { return var_; }
33   float Std() const;
34   float Pdf(float value) const;
35 
36  private:
37   int n_;
38   float sum_x_;
39   float sum_x2_;
40   float mean_;
41   float var_;
42   float exp_denom_;
43   float pdf_denom_;
44 };
45 
46 // Discrete-time implementation of a simple RC low-pass filter:
47 // exponentially-weighted moving average.
48 class RCFilter {
49  public:
RCFilter(float gain)50   explicit RCFilter(float gain)
51       : gain_(gain), n_(0), value_(0.0f) {}
52 
Add(float measurement)53   void Add(float measurement) {
54     value_ = n_++ ? gain_ * measurement + (1.0f - gain_) * value_ : measurement;
55   }
56 
Reset()57   void Reset() { n_ = 0; }
58 
NumMeasurements()59   int NumMeasurements() const { return n_; }
Output()60   float Output() const { return value_; }
61 
62  private:
63   float gain_;
64   int n_;
65   float value_;
66 };
67 
68 } // namespace filterfw
69 } // namespace android
70 
71 #endif  // ANDROID_FILTERFW_CORE_STATISTICS_H
72