How to display progress?

[Agagamand]

I need to calculate checksums of large files with a progress bar. I use this code, but the progress bar fills up before I get the hash. How to get the correct progress?

private string GetYYP_XXHash(string filename, IProgress<double> progress = null)
{
    byte[] buffer;
    byte[] oldBuffer;
    int bytesRead;
    int oldBytesRead;
    long size;
    long totalBytesRead = 0;

    using (Stream stream = File.OpenRead(filename))
    using (YYProject.XXHash.XXHash64 hashAlgorithm = YYProject.XXHash.XXHash64.Create())
    {
        size = stream.Length;
        buffer = new byte[1048576]; // 1MB buffer

        bytesRead = stream.Read(buffer, 0, buffer.Length);
        totalBytesRead += bytesRead;

        do
        {
            oldBytesRead = bytesRead;
            oldBuffer = buffer;

            buffer = new byte[Convert.ToInt32(BufferHash)];
            bytesRead = stream.Read(buffer, 0, buffer.Length);

            totalBytesRead += bytesRead;

            if (bytesRead == 0)
            {
                hashAlgorithm.TransformFinalBlock(oldBuffer, 0, oldBytesRead);
            }
            else
            {
                hashAlgorithm.TransformBlock(oldBuffer, 0, oldBytesRead, oldBuffer, 0);
            }

            progress?.Report((double)totalBytesRead * 100 / size);

        } while (bytesRead != 0);


        StringBuilder sBuilder = new StringBuilder();
        for (int i = 0; i < hashAlgorithm.Hash.Length; i++)
        {
            sBuilder.Append(hashAlgorithm.Hash[i].ToString("x2"));
        }

        return sBuilder.ToString();
    }
}