Utility function for calculating performance.

GeoHexPerformanceTest.cs

using System;
using NUnit.Framework;

namespace GeoHex
{
    [TestFixture]
    public class GeoHexPerformanceTest
    {
        [Test]
        public void Pow3Test()
        {
            const int MaxRepeat = 1000000;
            const int MaxLevel = 19;

            {
                TimeWatch.Reset();
                TimeWatch.Resume();

                for (int repeat = 0; repeat < MaxRepeat; repeat++)
                {
                    for (int i = 0; i < MaxLevel; i++)
                    {
                        Pow3.Calc(i);
                    }
                }

                TimeWatch.Pause(MaxLevel*MaxRepeat);
                TimeWatch.OutputResult("Pow3");
            }

            {
                TimeWatch.Reset();
                TimeWatch.Resume();

                for (int repeat = 0; repeat < MaxRepeat; repeat++)
                {
                    for (int i = 0; i < MaxLevel; i++)
                    {
                        Math.Pow(3,i);
                    }
                }

                TimeWatch.Pause(MaxLevel*MaxRepeat);
                TimeWatch.OutputResult("Math.Pow3");
            }
        }
    }
}

TimeWatch.cs

using System;
using System.IO;

public static class TimeWatch
{
    private static long _currentTime = 0;
    private static long _count = 0;
    private static long _totalTime = 0;

    public static void Reset()
    {
        _currentTime = 0;
        _totalTime = 0;
        _count = 0;
    }

    public static void Resume()
    {
        _currentTime = CurrentTimeMillis();
    }

    public static long Pause(int countup = 1)
    {
        long diff = CurrentTimeMillis() - _currentTime;
        _count += countup;
        _totalTime += diff;
        return diff;
    }

    public static void OutputResult(string tag)
    {
        PrintResult(tag);
        WriteResult(tag);
    }

    public static void PrintResult(string tag)
    {
        Console.WriteLine($"{tag}\t{_count}\t{_totalTime}\t{(double) _totalTime/_count}");
    }

    public static void WriteResult(string tag)
    {
        using (var sw = new StreamWriter(
            "/tmp/geohex_test.tsv",
            true,
            System.Text.Encoding.GetEncoding("utf-8")
            ))
        {
            sw.WriteLine($"{tag}\t{_count}\t{_totalTime}\t{(double) _totalTime/_count}");
            sw.Close();
        }
    }

    private static long CurrentTimeMillis()
    {
        System.DateTime epochStart = new System.DateTime(1970, 1, 1, 0, 0, 0, System.DateTimeKind.Utc);
        return (long) (System.DateTime.UtcNow - epochStart).TotalMilliseconds;
    }
}