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/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <stdlib.h>
#include <cpustats/CentralTendencyStatistics.h>
void CentralTendencyStatistics::sample(double x)
{
// update min and max
if (x < mMinimum)
mMinimum = x;
if (x > mMaximum)
mMaximum = x;
// Knuth
if (mN == 0) {
mMean = 0;
}
++mN;
double delta = x - mMean;
mMean += delta / mN;
mM2 += delta * (x - mMean);
}
void CentralTendencyStatistics::reset()
{
mMean = NAN;
mMedian = NAN;
mMinimum = INFINITY;
mMaximum = -INFINITY;
mN = 0;
mM2 = 0;
mVariance = NAN;
mVarianceKnownForN = 0;
mStddev = NAN;
mStddevKnownForN = 0;
}
double CentralTendencyStatistics::variance() const
{
double variance;
if (mVarianceKnownForN != mN) {
if (mN > 1) {
// double variance_n = M2/n;
variance = mM2 / (mN - 1);
} else {
variance = NAN;
}
mVariance = variance;
mVarianceKnownForN = mN;
} else {
variance = mVariance;
}
return variance;
}
double CentralTendencyStatistics::stddev() const
{
double stddev;
if (mStddevKnownForN != mN) {
stddev = sqrt(variance());
mStddev = stddev;
mStddevKnownForN = mN;
} else {
stddev = mStddev;
}
return stddev;
}
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