How Can I Compare Files in .NET More Efficiently Than Byte-by-Byte?

.NET efficient file comparison method

Comparing two files in .NET can be very time-consuming, especially for large files. The traditional method of reading binary files byte by byte and comparing them is inefficient and slow.

Alternative methods

To improve performance, consider the following alternatives:

File merging method

A surprisingly fast method is to concatenate the two files into a single byte array and compare the resulting values.

<code class="language-csharp">const int BYTES_TO_READ = sizeof(Int64);

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

    if (string.Equals(first.FullName, second.FullName, StringComparison.OrdinalIgnoreCase))
        return true;

    int iterations = (int)Math.Ceiling((double)first.Length / BYTES_TO_READ);

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

        for (int i = 0; i < iterations; i++)
        {
            fs1.Read(one, 0, BYTES_TO_READ);
            fs2.Read(two, 0, BYTES_TO_READ);
            if (!one.SequenceEqual(two))
                return false;
        }
    }
    return true;
}</code>

Checksum comparison

Another method is to generate a fingerprint of each file using a checksum algorithm such as CRC or MD5. Comparing these fingerprints is much faster than comparing entire files.

<code class="language-csharp">static bool FilesAreEqual_Hash(FileInfo first, FileInfo second)
{
    byte[] firstHash = MD5.Create().ComputeHash(first.OpenRead());
    byte[] secondHash = MD5.Create().ComputeHash(second.OpenRead());

    for (int i = 0; i < firstHash.Length; i++)
    {
        if (firstHash[i] != secondHash[i])
            return false;
    }
    return true;
}</code>

Performance comparison

In the test of large video files, the performance of the file merging method was approximately 3 times that of the byte-by-byte comparison method, while the hash comparison was faster, averaging about 865 milliseconds.

The best method depends on the size and nature of the files you want to compare. However, these alternatives provide significant performance improvements over traditional byte-by-byte comparison methods.

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