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A framework for writing performance micro-benchmarks using JUnit4 annotations, forked from https://github.com/carrotsearch/junit-benchmarks.

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package com.carrotsearch.junitbenchmarks;

import java.util.Locale;

/**
 * Average with standard deviation.
 */
public final class Average
{
    /**
     * Average (in milliseconds).
     */
    public final double avg;

    /**
     * Standard deviation (in milliseconds).
     */
    public final double stddev;

    /**
     * 
     */
    Average(double avg, double stddev)
    {
        this.avg = avg;
        this.stddev = stddev;
    }

    public String toString()
    {
        return String.format(Locale.ENGLISH, "%.2f [+- %.2f]", 
            avg, stddev);
    }

    static Average from(long [] values)
    {
        long sum = 0;
        long sumSquares = 0;

        for (long l : values)
        {
            sum += l;
            sumSquares += l * l;
        }

        double avg = sum / (double) values.length;
        return new Average(
            (sum / (double) values.length) / 1000.0, 
            Math.sqrt(sumSquares / (double) values.length - avg * avg) / 1000.0);
    }
}