How Can I Achieve Efficient File Comparison in .NET?

.NET efficient file comparison method

When comparing two files, speed is often of the essence. The traditional method of reading files byte by byte is very time consuming for large files. This article explores ways to do faster file comparisons in .NET, including checksum comparisons and custom byte array comparisons.

Checksum Comparison: Possible Solution?

Checksum comparisons (such as Cyclic Redundancy Check (CRC)) generate a unique fingerprint for each file. Comparing these fingerprints is faster than comparing the entire file byte by byte. However, it is important to note that checksums may produce false positives, so additional checks may be required to ensure accuracy.

Performance of checksum comparison:

While checksum comparison is faster than byte-by-byte comparison in some cases, it is not always the best solution. Our tests have shown that comparisons can always be completed in sub-seconds using the MD5 hashing algorithm.

Customize byte array comparison to optimize performance:

We propose a custom byte array comparison method that performs much better than byte-by-byte comparison. This method reads a block of bytes into an array and compares the array values ​​as integers. This parallelization reduces the overhead of individual byte comparisons.

Code example for byte array comparison:

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;
}

Test and Compare:

In our tests, custom byte array comparisons performed almost 3 times better than direct byte-by-byte comparisons. Although the hash method is slower than the byte array, it can always be completed within 1 second in the test.

By choosing the appropriate file comparison method based on file size and accuracy requirements, developers can achieve fast and efficient file comparison in .NET applications.

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