Calculating Md5 Hash of Big Files

Question

I want to make it very clear and simple. What if I have 1gb ram and I'm trying to calculate md5 hash of 2gb file? Currently, I'm doing it this way:

private static string Md5Hash(byte[] input)
{
    byte[] hash = MD5.Create().ComputeHash(input);
    StringBuilder builder = new StringBuilder(32);
    foreach(byte b in hash)
    { builder.Append(b.ToString("X2")); }
    return builder.ToString();
}

// I'm using it like: 'Md5.AsString(File.ReadAllBytes(filePath))'

So what are your suggestions?

Answer 1

Rather than computing the hash of the file after you've completely loaded it into memory, use the overload that takes a Stream.

byte[] hash;
using (Stream input = File.OpenRead("Filename"))
{
    hash = MD5.Create().ComputeHash(input);
}