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 #include <stdlib.h>
18 
19 #include <cpustats/CentralTendencyStatistics.h>
20 
sample(double x)21 void CentralTendencyStatistics::sample(double x)
22 {
23     // update min and max
24     if (x < mMinimum)
25         mMinimum = x;
26     if (x > mMaximum)
27         mMaximum = x;
28     // Knuth
29     if (mN == 0) {
30         mMean = 0;
31     }
32     ++mN;
33     double delta = x - mMean;
34     mMean += delta / mN;
35     mM2 += delta * (x - mMean);
36 }
37 
reset()38 void CentralTendencyStatistics::reset()
39 {
40     mMean = NAN;
41     mMedian = NAN;
42     mMinimum = INFINITY;
43     mMaximum = -INFINITY;
44     mN = 0;
45     mM2 = 0;
46     mVariance = NAN;
47     mVarianceKnownForN = 0;
48     mStddev = NAN;
49     mStddevKnownForN = 0;
50 }
51 
variance() const52 double CentralTendencyStatistics::variance() const
53 {
54     double variance;
55     if (mVarianceKnownForN != mN) {
56         if (mN > 1) {
57             // double variance_n = M2/n;
58             variance = mM2 / (mN - 1);
59         } else {
60             variance = NAN;
61         }
62         mVariance = variance;
63         mVarianceKnownForN = mN;
64     } else {
65         variance = mVariance;
66     }
67     return variance;
68 }
69 
stddev() const70 double CentralTendencyStatistics::stddev() const
71 {
72     double stddev;
73     if (mStddevKnownForN != mN) {
74         stddev = sqrt(variance());
75         mStddev = stddev;
76         mStddevKnownForN = mN;
77     } else {
78         stddev = mStddev;
79     }
80     return stddev;
81 }
82