Bug 483621: Move segment store statistics into timing analysis plug-ins

[deliverable/tracecompass.git] / analysis / org.eclipse.tracecompass.analysis.timing.core / src / org / eclipse / tracecompass / internal / analysis / timing / core / segmentstore / statistics / SegmentStoreStatistics.java

diff --git a/analysis/org.eclipse.tracecompass.analysis.timing.core/src/org/eclipse/tracecompass/internal/analysis/timing/core/segmentstore/statistics/SegmentStoreStatistics.java b/analysis/org.eclipse.tracecompass.analysis.timing.core/src/org/eclipse/tracecompass/internal/analysis/timing/core/segmentstore/statistics/SegmentStoreStatistics.java
new file mode 100644 (file)
index 0000000..892c404
--- /dev/null
+++ b/analysis/org.eclipse.tracecompass.analysis.timing.core/src/org/eclipse/tracecompass/internal/analysis/timing/core/segmentstore/statistics/SegmentStoreStatistics.java
@@ -0,0 +1,112 @@
+/*******************************************************************************
+ * Copyright (c) 2015, 2016 Ericsson
+ *
+ * All rights reserved. This program and the accompanying materials are made
+ * available under the terms of the Eclipse Public License v1.0 which
+ * accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Bernd Hufmann - Initial API and implementation
+ *******************************************************************************/
+package org.eclipse.tracecompass.internal.analysis.timing.core.segmentstore.statistics;
+
+import org.eclipse.tracecompass.segmentstore.core.ISegment;
+
+/**
+ * Class to calculate simple segment store statistics (min, max, average)
+ *
+ * @author Bernd Hufmann
+ */
+public class SegmentStoreStatistics {
+    private long fMin;
+    private long fMax;
+    private long fNbSegments;
+    private double fAverage;
+    private double fVariance;
+
+    /**
+     * Constructor
+     */
+    public SegmentStoreStatistics() {
+        fMin = Long.MAX_VALUE;
+        fMax = Long.MIN_VALUE;
+        fNbSegments = 0;
+        fAverage = 0.0;
+        fVariance = 0.0;
+    }
+
+    /**
+     * Get minimum value
+     *
+     * @return minimum value
+     */
+    public long getMin() {
+        return fMin;
+    }
+
+    /**
+     * Get maximum value
+     *
+     * @return maximum value
+     */
+    public long getMax() {
+        return fMax;
+    }
+
+    /**
+     * Get number of segments analyzed
+     *
+     * @return number of segments analyzed
+     */
+    public long getNbSegments() {
+        return fNbSegments;
+    }
+
+    /**
+     * Gets the arithmetic average
+     *
+     * @return arithmetic average
+     */
+    public double getAverage() {
+        return fAverage;
+    }
+
+    /**
+     * Gets the standard deviation of the segments, uses the online algorithm
+     * shown here <a href=
+     * "https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Online_algorithm">
+     * Wikipedia article of dec 3 2015 </a>
+     *
+     * @return the standard deviation of the segment store, will return NaN if
+     *         there are less than 3 elements
+     */
+    public double getStdDev() {
+        return fNbSegments > 2 ? Math.sqrt(fVariance / (fNbSegments - 1)) : Double.NaN;
+    }
+
+    /**
+     * Update the statistics based on a given segment
+     * <p>
+     * This is an online algorithm and must retain a complexity of O(1)
+     *
+     * @param segment
+     *            the segment used for the update
+     */
+    public void update(ISegment segment) {
+        long value = segment.getLength();
+        /*
+         * Min and max are trivial, as well as number of segments
+         */
+        fMin = Math.min(fMin, value);
+        fMax = Math.max(fMax, value);
+
+        fNbSegments++;
+        /*
+         * The running mean is not trivial, see proof in javadoc.
+         */
+        double delta = value - fAverage;
+        fAverage += delta / fNbSegments;
+        fVariance += delta * (value - fAverage);
+    }
+}