Performance of Buffer.BlockCopy on multidimensional arrays

gistfile1.txt

// Begin linqpad script

void Main()
{
	var sourceIndex = 3;
	var source = new double[5,1000];
	
	for(int i = 0; i < source.GetLength(1); i++){
		source[sourceIndex, i] = i + 1;
	}
	
	// for loop
	Action<double[,]> func1 = (s) => {
		var length = s.GetLength(1);
		var target0 = new double[length];
		var target1 = new double[length];
		var target2 = new double[length];
		var target3 = new double[length];
		var target4 = new double[length];
		
		for(int i = 0; i < length; i++){
			target0[i] = s[0, i];
			target1[i] = s[1, i];
			target2[i] = s[2, i];
			target3[i] = s[3, i];
			target4[i] = s[4, i];
		}
	};
	
	// block copy
	Action<double[,]> func2 = (s) => {
		var length = s.GetLength(1);
		var size = sizeof(double);
		var byteLength = size * length;
		
		var target0 = new double[length];
		var target1 = new double[length];
		var target2 = new double[length];
		var target3 = new double[length];
		var target4 = new double[length];
		
		Buffer.BlockCopy(source, byteLength * 0, target0, 0, byteLength);
		Buffer.BlockCopy(source, byteLength * 1, target0, 0, byteLength);
		Buffer.BlockCopy(source, byteLength * 2, target0, 0, byteLength);
		Buffer.BlockCopy(source, byteLength * 3, target0, 0, byteLength);
		Buffer.BlockCopy(source, byteLength * 4, target0, 0, byteLength);
	};
	
	Benchmark
		.For(1000)
			.Execute("For Loop", () => func1(source))
			.Execute("Buffer  ", () => func2(source))
		.Report(4).Dump();
}

public static class Benchmark
{
	public static BenchmarkActionScheduler For(int count)
	{
		Process.GetCurrentProcess().ProcessorAffinity = new IntPtr(1);
		return new BenchmarkActionScheduler(count);
	}
}

public class BenchmarkActionScheduler
	: IBenchmarkActionScheduler
{
	private readonly int count;
	private readonly IDictionary<string, Action> actionDictionary =
		new Dictionary<string, Action>();
	private int actionIndex;
	
	internal BenchmarkActionScheduler(int count)
	{
		this.count = count;
	}
	
	public IBenchmarkActionScheduler Execute(Action action)
	{
		return Execute((actionIndex++).ToString(), action);
	}
	
	public IBenchmarkActionScheduler Execute(string name, Action action)
	{
		actionDictionary.Add(name, action);
		return this;
	}

	IEnumerable<Report> IBenchmarkActionScheduler.Report(int? digits)
	{
		var reportList = new List<Report>();
		
		foreach (var action in actionDictionary)
		{
			GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced, true);

			var stopwatch = Stopwatch.StartNew();
			var localAction = action;
			
			Enumerable
				.Range(0, count)
				.Iterate(() => localAction.Value());

			reportList
				.Add(new Report(action.Key, stopwatch.ElapsedMilliseconds));
		}
		
		var maxTime = reportList.Max(x => x.Milliseconds);
		
		foreach (var report in reportList)
		{
			var percentage = (report.Milliseconds * 100) / (double)maxTime;
			
			if (digits.HasValue)
			{
				percentage = Math.Round(percentage, digits.Value);
			}
			
			report.Percentage = percentage;
			report.TimesFaster = Math.Round((double)maxTime / (double)report.Milliseconds, digits.Value);
		}
		
		return reportList;		
	}
}

public interface IBenchmarkActionScheduler
{
	IEnumerable<Report> Report(int? digits = null);

	IBenchmarkActionScheduler Execute(Action action);

	IBenchmarkActionScheduler Execute(string name, Action action);
}

public class Report
{
	public Report(string operationName, long milliseconds)
	{
		OperationName = operationName;
		Milliseconds = milliseconds;
	}
	
	public string OperationName { get; private set; }
	
	public long Milliseconds { get; private set; }
	
	public double Percentage { get; internal set; }
	
	public double TimesFaster { get; internal set; }
}

public static class EnumerableExensions
{
	public static void Iterate<T>(this IEnumerable<T> collection)
	{
		var enumerator = collection.GetEnumerator();

		while (enumerator.MoveNext())
		{
		}
	}
	
	public static void Iterate<T>(this IEnumerable<T> collection, Action action)
	{
		var enumerator = collection.GetEnumerator();
		
		while (enumerator.MoveNext())
		{
			action();
		}
	}
}