C# 128 Bit ASynchronous File Hashing Class using the MurMur3 Hashing Algorithm

FileHash128.cs

public class FileHash128 : Murmur3
{
    private const    int    BufferSize = 1024 * 80;
    private readonly byte[] buffer     = new byte[1073741823];
    public byte[] GetFileHashSync(string path)
    {
        var fLen = 0;
        using(var fileStream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, BufferSize, false))
        {
            var offset = 0;
            var length = fileStream.Length;
            if(length > 1073741823)
                throw new ArgumentOutOfRangeException("File Size exceeds 1gb.");
            var count = (int) length;
            fLen = count;
            int nRead;
            while(count > 0)
            {
                nRead = fileStream.Read(buffer, offset, count);
                if(nRead == 0)
                    break;
                offset += nRead;
                count  -= nRead;
            }
        }
        return ComputeHash(buffer, 0, fLen);
    }
    public async Task<byte[]> GetFileHashAsync(string path)
    {
        var fLen = 0;
        using(var fileStream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, BufferSize, true))
        {
            var offset = 0;
            var count  = (int) fileStream.Length;
            if(count > 1073741823)
                throw new ArgumentOutOfRangeException("File Size exceeds 1gb.");
            fLen = count;
            while(count > 0)
            {
                var nRead = await fileStream.ReadAsync(buffer, offset, count).ConfigureAwait(false);
                if(nRead == 0)
                    break;
                offset += nRead;
                count  -= nRead;
            }
        }
        return ComputeHash(buffer, 0, fLen);
    }
}