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
20namespace android {
21namespace filterfw {
22
23// An incrementally-constructed Normal distribution.
24class IncrementalGaussian {
25 public:
26  IncrementalGaussian();
27
28  void Add(float value);
29
30  float NumSamples() const { return n_; }
31  float Mean() const { return mean_; }
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.
48class RCFilter {
49 public:
50  explicit RCFilter(float gain)
51      : gain_(gain), n_(0), value_(0.0f) {}
52
53  void Add(float measurement) {
54    value_ = n_++ ? gain_ * measurement + (1.0f - gain_) * value_ : measurement;
55  }
56
57  void Reset() { n_ = 0; }
58
59  int NumMeasurements() const { return n_; }
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