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
21void 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
38void 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
52double 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
70double 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