Can Checksumming and Chunk Comparison Speed Up File Comparison in .NET?

.NET efficient file comparison technology

Comparing files byte by byte is a common method, but it is inefficient. This article explores faster methods of comparing files and introduces libraries in .NET for generating checksums.

Can checksum comparison improve speed?

Yes, using algorithms such as CRC for checksum comparison is faster than the byte-by-byte method. Checksums generate a unique signature for each file, allowing signatures to be compared rather than entire files.

.NET file checksum generation library

Multiple .NET libraries provide file checksum generation capabilities:

• System.Security.Cryptography.MD5: Generate MD5 checksum of the file.
• System.Security.Cryptography.SHA1: Calculate the SHA1 checksum of the file.
• System.Security.Cryptography.SHA256: Calculate the SHA256 checksum of the file.
• System.Security.Cryptography.SHA512: Generate SHA512 checksum of the file.

Optimized comparison method

While hashing is a fast method, you can further optimize file comparisons using a method that reads large chunks of bytes and compares them as numbers:

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++)
        {
            int read1 = fs1.Read(one, 0, BYTES_TO_READ);
            int read2 = fs2.Read(two, 0, BYTES_TO_READ);

            if (read1 != read2 || !one.SequenceEqual(two))
                return false;
        }
    }

    return true;
}

Performance test results

Performance testing shows that for large files (such as a 100MB video file), comparing file blocks as numbers outperforms byte-by-byte comparisons and hashes:

• Block comparison: 1063ms
• Byte-by-byte comparison: 3031ms
• Hash: 865ms

For smaller files, hashing is usually faster due to its optimized nature. However, for large files, the overhead of reading and processing the entire file can be significant, and the block comparison method is faster.

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