Most efficient way to compare a memorystream to a file C# .NET

Another solution:

private static bool CompareMemoryStreams(MemoryStream ms1, MemoryStream ms2)
{
    if (ms1.Length != ms2.Length)
        return false;
    ms1.Position = 0;
    ms2.Position = 0;

    var msArray1 = ms1.ToArray();
    var msArray2 = ms2.ToArray();

    return msArray1.SequenceEqual(msArray2);
}

Firstly, getting hashcode of the two streams won't help - to calculate hashcodes, you'd need to read the entire contents and perform some simple calculation while reading. If you compare the files byte-by-byte or using buffers, then you can stop earlier (after you find first two bytes/blocks) that don't match.

However, this approach would make sense if you needed to compare the MemoryStream against multiple files, because then you'd need to loop through the MemoryStream just once (to calculate the hashcode) and tne loop through all the files.

In any case, you'll have to write code to read the entire file. As you mentioned, this can be done either byte-by-byte or using buffers. Reading data into buffer is a good idea, because it may be more efficient operation when reading from HDD (e.g. reading 1kB buffer). Moreover, you could use asynchronous BeginRead method if you need to process multiple files in parallel.

Summary:

• If you need to compare multiple files, use hashcode
• To read/compare content of single file:
  • Read 1kB of data into a buffer from both streams
  • See if there is a difference (if yes, quit)
  • Continue looping

Implement the above steps asynchronously using BeginRead if you need to process mutliple files in parallel.