Splits a large file into smaller files, and merges them back into the original one.

FileSplitMerge.cs

using System;
using System.IO;

class Program
{
    const int SplitSize = 1024 * 1024 * 1024;   // Splits into 1GB files
    const int BufferSize = 1024 * 1024;         // using 1MB size buffer

    static void Main(string[] args)
    {
        if (args.Length == 1)
        {
            // Split(args[0]);
            // Merge(args[0]);
        }
        else if (args.Length == 2)
        {
            var result = Compare(args[0], args[1]);
            Console.WriteLine(result ? "Identical" : "Different");
        }
    }

    static void Split(string name)
    {
        var input = new FileStream(name, FileMode.Open, FileAccess.Read, FileShare.None);
        Console.WriteLine("Split input file: {0}", name);

        var size = (input.Length / SplitSize) + (input.Length % SplitSize == 0 ? 0 : 1);
        Console.WriteLine("Generates {0} files ({1} bytes each)", size, SplitSize);

        var buf = new byte[BufferSize];
        var placeholder = new string('0', (int)Math.Floor(Math.Log10(size)) + 1);
        for (var i = 0; i < size; )
        {
            var output = new FileStream(name + "." + (++i).ToString(placeholder),
                FileMode.CreateNew, FileAccess.Write, FileShare.None);
            Console.WriteLine("=== {0}/{1} ===", i, size);
            for (var j = 0; j < SplitSize; )
            {
                var read = input.Read(buf, 0, Math.Min(BufferSize, SplitSize - j));
                if (read == 0) break;
                output.Write(buf, 0, read);
                j += read;
                Console.Write('.');
            }
            output.Close();
            Console.WriteLine();
        }

        input.Close();
        Console.WriteLine("End");
    }

    static void Merge(string name)
    {
        var f = new FileInfo(name);
        var t = f.Name.LastIndexOf('.');
        var len = f.Name.Length - t - 1;
        if (len >= 9)
        {
            Console.WriteLine("Too many split?");
            return;
        }

        var max = (int)Math.Pow(10, len);
        var placeholder = new string('0', len);
        var baseName = name.Substring(0, name.Length - (len + 1));
        var output = new FileStream(baseName,
            FileMode.CreateNew, FileAccess.Write, FileShare.None);
        Console.WriteLine("Merge output file: {0}", baseName);
        var buf = new byte[BufferSize];
        for (var i = 1; i < max; i++)
        {
            name = baseName + "." + i.ToString(placeholder);
            if (!File.Exists(name)) break;

            var input = new FileStream(name, FileMode.Open, FileAccess.Read, FileShare.None);
            Console.WriteLine("=== {0} ===", i);
            for (var j = 0; j < input.Length; )
            {
                var read = input.Read(buf, 0, BufferSize);
                if (read == 0) break;
                output.Write(buf, 0, read);
                j += read;
                Console.Write('.');
            }
            input.Close();
            Console.WriteLine();
        }

        output.Close();
        Console.WriteLine("End");
    }

    static bool Compare(string f1, string f2)
    {
        var files = new[] { f1, f2 };
        Console.WriteLine("Comparing files:\n{0}\n{1}", f1, f2);

        var f = new FileStream[2];
        var buf = new byte[2][];
        for (var i = 0; i < 2; i++)
        {
            f[i] = new FileStream(files[i], FileMode.Open, FileAccess.Read, FileShare.None);
            buf[i] = new byte[BufferSize];
        }

        try
        {
            if (f[0].Length != f[1].Length) return false;
            else
                for (var j = 0L; j < f[0].Length; )
                {
                    var read = 0;
                    for (var i = 0; i < 2; i++)
                    {
                        read = 0;
                        while (read < BufferSize)
                        {
                            var now = f[i].Read(buf[i], read, BufferSize - read);
                            if (now == 0) break;
                            read += now;
                        }
                    }
                    j += read;

                    for (var i = 0; i < read; i++)
                        if (buf[0][i] != buf[1][i])
                            return false;

                    Console.Write('.');
                }

            return true;
        }
        finally
        {
            Console.WriteLine();
            f[0].Close();
            f[1].Close();
        }
    }
}