Span Memmove Benchmark

Program.cs

using System;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

public class Program
{
    static void Main(string[] args)
    {
        BenchmarkRunner.Run<Program>();
    }

    [Benchmark]
    public void ArrayCopy()
    {
        var array1 = "this is a test".ToCharArray();
        var array2 = new char[array1.Length];
        
        Array.Copy(array1, 0, array2, 0, array1.Length);
    }

    [Benchmark]
    public void BufferBlockCopy()
    {
        var array1 = "this is a test".ToCharArray();
        var array2 = new char[array1.Length];

        Buffer.BlockCopy(array1, 0, array2, 0, array1.Length);
    }

    [Benchmark]
    public void SpanCopy()
    {
        var array1 = "this is a test".AsSpan();
        var array2 = new char[array1.Length].AsSpan();
        
        Span.Copy(array1, 0, array2, 0, array1.Length);
    }

    [Benchmark]
    public void SpanCopyStackAlloc()
    {
        var array1 = "this is a test".AsSpan();
        Span<char> array2 = stackalloc char[array1.Length];
        
        Span.Copy(array1, 0, array2, 0, array1.Length);
    }
}

public static class Span
{
    public static void Copy<T>(ReadOnlySpan<T> src, int sStart, Span<T> dest, int dStart, int len)
    {
        if (dest.Length < src.Length)
        {
            int i = 0;
            while (len-- > 0 && dStart + i < dest.Length)
            {
                dest[dStart + i] =  src[sStart + i];
                i += 1;
            }
        }
        else
        {
            int lastS = sStart + (len - 1);
            int lastD = dStart + (len - 1);
            int i = 0;
            while (len-- > 0)
            {
                dest[lastD - i] =  src[lastS - i];
                i += 1;
            }
        }
    }
}

.NET Core 2.1

// * Summary *

BenchmarkDotNet=v0.11.5, OS=Windows 10.0.18362
Intel Core i7-6700K CPU 4.00GHz (Skylake), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=3.0.100
[Host] : .NET Core 2.1.12 (CoreCLR 4.6.27817.01, CoreFX 4.6.27818.01), 64bit RyuJIT
DefaultJob : .NET Core 2.1.12 (CoreCLR 4.6.27817.01, CoreFX 4.6.27818.01), 64bit RyuJIT

Method	Mean	Error	StdDev
ArrayCopy	22.71 ns	0.1647 ns	0.1375 ns
BufferBlockCopy	23.02 ns	0.5288 ns	1.5591 ns
SpanCopy	28.11 ns	0.7507 ns	1.0766 ns
SpanCopyStackAlloc	24.64 ns	0.5107 ns	0.5015 ns

.NET Core 3.0

// * Summary *

BenchmarkDotNet=v0.11.5, OS=Windows 10.0.18362
Intel Core i7-6700K CPU 4.00GHz (Skylake), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=3.0.100
[Host] : .NET Core 3.0.0 (CoreCLR 4.700.19.46205, CoreFX 4.700.19.46214), 64bit RyuJIT
DefaultJob : .NET Core 3.0.0 (CoreCLR 4.700.19.46205, CoreFX 4.700.19.46214), 64bit RyuJIT

Method	Mean	Error	StdDev
ArrayCopy	22.38 ns	0.4569 ns	0.5940 ns
BufferBlockCopy	20.06 ns	0.1306 ns	0.1222 ns
SpanCopy	19.95 ns	0.3644 ns	0.3043 ns
SpanCopyStackAlloc	23.81 ns	0.1139 ns	0.1065 ns