analysis/org.eclipse.tracecompass.analysis.timing.core/src/org/eclipse/tracecompass/analysis/timing/core/segmentstore/statistics/SegmentStoreStatistics.java

   1 /*******************************************************************************
   2  * Copyright (c) 2015, 2016 Ericsson
   3  *
   4  * All rights reserved. This program and the accompanying materials are made
   5  * available under the terms of the Eclipse Public License v1.0 which
   6  * accompanies this distribution, and is available at
   7  * http://www.eclipse.org/legal/epl-v10.html
   8  *
   9  * Contributors:
  10  *     Bernd Hufmann - Initial API and implementation
  11  *******************************************************************************/
  12 package org.eclipse.tracecompass.analysis.timing.core.segmentstore.statistics;
  13
  14 import org.eclipse.tracecompass.segmentstore.core.BasicSegment;
  15 import org.eclipse.tracecompass.segmentstore.core.ISegment;
  16
  17 /**
  18  * Class to calculate simple segment store statistics (min, max, average)
  19  *
  20  * @author Bernd Hufmann
  21  */
  22 public class SegmentStoreStatistics {
  23     private ISegment fMin;
  24     private ISegment fMax;
  25     private long fNbSegments;
  26     private double fAverage;
  27     private double fVariance;
  28     private double fTotal;
  29
  30     /**
  31      * Constructor
  32      */
  33     public SegmentStoreStatistics() {
  34         fMin = new BasicSegment(0, Long.MAX_VALUE);
  35         fMax = new BasicSegment(Long.MIN_VALUE, 0);
  36         fNbSegments = 0;
  37         fAverage = 0.0;
  38         fVariance = 0.0;
  39         fTotal = 0.0;
  40     }
  41
  42     /**
  43      * Get minimum value
  44      *
  45      * @return minimum value
  46      */
  47     public long getMin() {
  48         return fMin.getLength();
  49     }
  50
  51     /**
  52      * Get maximum value
  53      *
  54      * @return maximum value
  55      */
  56     public long getMax() {
  57         return fMax.getLength();
  58     }
  59
  60     /**
  61      * Get segment with minimum length
  62      *
  63      * @return segment with minimum length
  64      */
  65     public ISegment getMinSegment() {
  66         return fMin;
  67     }
  68
  69     /**
  70      * Get segment with maximum length
  71      *
  72      * @return segment with maximum length
  73      */
  74     public ISegment getMaxSegment() {
  75         return fMax;
  76     }
  77
  78     /**
  79      * Get number of segments analyzed
  80      *
  81      * @return number of segments analyzed
  82      */
  83     public long getNbSegments() {
  84         return fNbSegments;
  85     }
  86
  87     /**
  88      * Gets the arithmetic average
  89      *
  90      * @return arithmetic average
  91      */
  92     public double getAverage() {
  93         return fAverage;
  94     }
  95
  96     /**
  97      * Gets the standard deviation of the segments, uses the online algorithm
  98      * shown here <a href=
  99      * "https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Online_algorithm">
 100      * Wikipedia article of dec 3 2015 </a>
 101      *
 102      * @return the standard deviation of the segment store, will return NaN if
 103      *         there are less than 3 elements
 104      */
 105     public double getStdDev() {
 106         return fNbSegments > 2 ? Math.sqrt(fVariance / (fNbSegments - 1)) : Double.NaN;
 107     }
 108
 109     /**
 110      * Update the statistics based on a given segment
 111      * <p>
 112      * This is an online algorithm and must retain a complexity of O(1)
 113      *
 114      * @param segment
 115      *            the segment used for the update
 116      */
 117     public void update(ISegment segment) {
 118         long value = segment.getLength();
 119         /*
 120          * Min and max are trivial, as well as number of segments
 121          */
 122         long min = fMin.getLength();
 123         long max = fMax.getLength();
 124         fMin = min <= value ? fMin : segment;
 125         fMax = max >= value ? fMax : segment;
 126
 127         fNbSegments++;
 128         /*
 129          * The running mean is not trivial, see proof in javadoc.
 130          */
 131         double delta = value - fAverage;
 132         fAverage += delta / fNbSegments;
 133         fVariance += delta * (value - fAverage);
 134         fTotal += value;
 135     }
 136
 137     /**
 138      * Get total value
 139      *
 140      * @return total value
 141      * @since 1.1
 142      */
 143     public double getTotal() {
 144         return fTotal;
 145     }
 146 }