void Main()
{
    var array = new byte[10000000];

    var initBlk = new InitblkMemoryHelper();
    var loop = new LoopMemoryHelper();
    
    // First run for JIT warmup and type initialization
    initBlk.Memset(array, 0, array.Length, 42);
    loop.Memset(array, 0, array.Length, 42);
    
    int iterations = 1000;
    Test("InitBlk", initBlk, array, iterations);
    Test("Loop", loop, array, iterations);
}

void Test(string name, IMemoryHelper helper,  byte[] array, int iterations)
{
    Stopwatch sw = Stopwatch.StartNew();
    for (int i = 0; i < iterations; i++)
    {
        helper.Memset(array, 0, array.Length, 42);
    }
    sw.Stop();
    sw.Elapsed.Dump(name);
}

interface IMemoryHelper
{
    void Memset(byte[] array, int start, int count, byte value);
}

class LoopMemoryHelper : IMemoryHelper
{
    public void Memset(byte[] array, int start, int count, byte value)
    {
        int upper = start + count;
        for (int i = start; i < upper; i++)
        {
            array[i] = value;
        }
    }
}

class InitblkMemoryHelper : IMemoryHelper
{
    private delegate void MemorySetter(IntPtr array, byte value, int count);
    private static readonly MemorySetter _memset;
    static InitblkMemoryHelper()
    {
        _memset = CreateMemset();
    }

    private static MemorySetter CreateMemset()
    {
        var m = new DynamicMethod(
            "memset",
            MethodAttributes.Public | MethodAttributes.Static,
            CallingConventions.Standard,
            typeof(void),
            new[] { typeof(IntPtr), typeof(byte), typeof(int) },
            typeof(InitblkMemoryHelper),
            false);
        var il = m.GetILGenerator();
        il.Emit(OpCodes.Ldarg_0); // address
        il.Emit(OpCodes.Ldarg_1); // initialization value
        il.Emit(OpCodes.Ldarg_2); // number of bytes
        il.Emit(OpCodes.Initblk);
        il.Emit(OpCodes.Ret);
        return (MemorySetter)m.CreateDelegate(typeof(MemorySetter));
    }
    
    public void Memset(byte[] array, int start, int count, byte value)
    {
        GCHandle h = default(GCHandle);
        try
        {
            h = GCHandle.Alloc(array, GCHandleType.Pinned);
            IntPtr addr = h.AddrOfPinnedObject() + start;
            _memset(addr, value, count);
        }
        finally
        {
            if (h.IsAllocated)
                h.Free();
        }
    }
}