Hello Crauzer,

and thanks a lot for the implementation!
I have one request, if you don't mind :)

Could you please make Update(...) and Digest64() public?

The reason is: I would like to use your work in a pipeline of streams. With a hashing stream acting as a filter or facade.
Your current implementation allows for an input stream, I need to initialize with output streams, though.

My implementation of such a Stream goes like this:

    public class HashingStream : Stream
    {
        readonly XXHash3 _hash = XXHash3.Create();

        private readonly Stream _destination;

        public HashingStream(Stream destination)
        {
            _destination = destination;
        }

        public Hash Hash { get; private set; }

        public override void Write(byte[] buffer, int offset, int count)
        {
            _destination.Write(buffer, offset, count);

            _hash.Update(new ReadOnlySpan<byte>(buffer, offset, count));
        }

        protected override void Dispose(bool disposing)
        {
            Hash = new Hash(_hash.Digest64());

            base.Dispose(disposing);
        }

And that's why I would like to have public access to these methods.

You have also ported the ZStd compression, which I use, too.
The pattern is something like:

Stream input = File.OpenRead(...);

var output = File.OpenWrite(...);
var compressing = new CompressingStream(output);
var hashing = new HashingStream(compressing);

using (hashing)
{
    input.CopyTo(hashing);
}

var hash = hashing.Hash;

If you would see such a stream in your repo, I'd be happy to propose a PR.

Cheerio,
Andreas

This is a good request!

I initially had the methods as public but got led astray while looking at how the .NET standard library implements hashing interfaces and forgot that this is a valid use-case.

I will look into exposing those methods as public this or next week.