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 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 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 52 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 70 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
