List<T> readonly maken en bestanden filteren bij iteratie

var files_grouped_by_length = new DirectoryInfo(@"G:\sampling")
                .GetFiles("*.*", SearchOption.AllDirectories)
                .GroupBy(f => f.Length)     //Files grouped by filesize 
                .Where(g => g.Count() > 1); //We're only interested in groups with more than 1 file

public bool CompareFiles(FileInfo left, FileInfo right)
{
    if (left.Length != right.Length)
        return false;

    Int64 l = 0, r = 0;         //"Buffers"
    long p = 0,                 //Position
         i = left.Length / 8,   //Iterations of "int64-sized reads"
         c = left.Length % 8;   //Rest

    using (var brl = new BinaryReader(left.OpenRead()))
    using (var brr = new BinaryReader(right.OpenRead()))
    {
        //Compare "int64 chunks" at a time
        while (l == r && p++ < i)
        {
            l = brl.ReadInt64();
            r = brr.ReadInt64();
        }

        //Compare remaining bytes (if any and the left still equalled right in the last read)
        if (l == r && c > 0)
        {
            p = 0;  //Reset position
            while (l == r && p++ < c)
            {
                l = brl.ReadByte();
                r = brr.ReadByte();
            }
        }
    }
    return l == r;
}

//Oorspronkelijk:
using (var brl = new BinaryReader(left.OpenRead()))
using (var brr = new BinaryReader(right.OpenRead()))

//4Kb per keer
using var brl = new BinaryReader(new BufferedStream(left.OpenRead(), 4 * 1024)))
using (var brr = new BinaryReader(new BufferedStream(right.OpenRead(), 4 * 1024)))

//128Kb per keer
using (var brl = new BinaryReader(new BufferedStream(left.OpenRead(), 128 * 1024)))
using var brr = new BinaryReader(new BufferedStream(right.OpenRead(), 128 * 1024)))

//1MB per keer
using (var brl = new BinaryReader(new BufferedStream(left.OpenRead(), 1024 * 1024)))
using (var brr = new BinaryReader(new BufferedStream(right.OpenRead(), 1024 * 1024)))

        [DllImport("msvcrt.dll", CallingConvention = CallingConvention.Cdecl)]
        static extern int memcmp(byte[] b1, byte[] b2, long count);

        private static bool ReadFully(Stream f, byte[] buf, int count)
        {
            int offset = 0;
            while (count > 0)
            {
                int read = f.Read(buf, offset, count);
                if (read <= 0)
                    return false;
                offset += read;
                count -= read;
            }
            return true;
        }

        public static bool CompareFiles(FileInfo first, FileInfo second)
        {
            if (first.Length != second.Length)
            {
                return false;
            }

            using (FileStream fs1 = first.OpenRead())
            using (FileStream fs2 = second.OpenRead())
            {
                byte[] one = new byte[1 << 17];
                byte[] two = new byte[1 << 17];

                int read = fs1.Read(one, 0, 4096);
                if (!(ReadFully(fs2, two, read) && (memcmp(one, two, read) == 0)))
                    return false;

                while ((read = fs1.Read(one, 0, one.Length)) > 0)
                {
                    if (!(ReadFully(fs2, two, read) && (memcmp(one, two, read) == 0)))
                        return false;
                }

                return true;
            }
        }