TorrentHardLinkHelper.Locate.TorrentFileLocater.CheckPiece C# (CSharp) Method

        private bool CheckPiece(int pieceIndex)
        {
            bool result;
            if (this._pieceCheckedReusltsDictionary.TryGetValue(pieceIndex, out result))
            {
                return result;
            }
            ulong startPos = (ulong)pieceIndex * (ulong)this._torrent.PieceLength;
            ulong pos = 0;
            ulong writenLength = 0;
            var filePieces = new List<FileLinkPiece>();
            foreach (TorrentFileLink fileLink in this._torrentFileLinks)
            {
                if (pos + (ulong)fileLink.TorrentFile.Length >= startPos)
                {
                    ulong readPos = startPos - pos;
                    ulong readLength = (ulong)fileLink.TorrentFile.Length - readPos;
                    if (writenLength + readLength > (ulong)this._torrent.PieceLength)
                    {
                        readLength = (ulong)this._torrent.PieceLength - writenLength;
                    }

                    var filePiece = new FileLinkPiece
                    {
                        FileLink = fileLink,
                        ReadLength = readLength,
                        StartPos = readPos
                    };
                    filePieces.Add(filePiece);

                    writenLength += readLength;
                    startPos += readLength;
                    if (writenLength == (ulong)this._torrent.PieceLength)
                    {
                        break;
                    }
                }
                pos += (ulong)fileLink.TorrentFile.Length;
            }

            var hash = new HashFileLinkPieces(this._torrent, pieceIndex, filePieces);
            string pattern = hash.Run();
            if (string.IsNullOrEmpty(pattern))
            {
                foreach (FileLinkPiece piece in filePieces)
                {
                    if (piece.FileLink.State == LinkState.NeedConfirm)
                    {
                        piece.FileLink.State = LinkState.Fail;
                    }
                }
                this._pieceCheckedReusltsDictionary.Add(pieceIndex, false);
                return false;
            }
            for (int i = 0; i < filePieces.Count; i++)
            {
                if (filePieces[i].FileLink.State == LinkState.NeedConfirm)
                {
                    filePieces[i].FileLink.LinkedFsFileIndex = int.Parse(pattern.Split(',')[i]);
                    filePieces[i].FileLink.LinkedFsFileInfo.Located = true;
                    filePieces[i].FileLink.State = LinkState.Located;
                }
            }
            this._pieceCheckedReusltsDictionary.Add(pieceIndex, true);
            return true;
        }