Crisis.Ionic.Zip.ZipEntry.FigureCrc32 C# (CSharp) Method

        private Int32 FigureCrc32()
        {
            if (_crcCalculated == false)
            {
                Stream input = null;
                // get the original stream:
                if (this._Source == ZipEntrySource.WriteDelegate)
                {
                    var output = new Crisis.Ionic.Crc.CrcCalculatorStream(Stream.Null);
                    // allow the application to write the data
                    this._WriteDelegate(this.FileName, output);
                    _Crc32 = output.Crc;
                }
                else if (this._Source == ZipEntrySource.ZipFile)
                {
                    // nothing to do - the CRC is already set
                }
                else
                {
                    if (this._Source == ZipEntrySource.Stream)
                    {
                        PrepSourceStream();
                        input = this._sourceStream;
                    }
                    else if (this._Source == ZipEntrySource.JitStream)
                    {
                        // allow the application to open the stream
                        if (this._sourceStream == null)
                            _sourceStream = this._OpenDelegate(this.FileName);
                        PrepSourceStream();
                        input = this._sourceStream;
                    }
                    else if (this._Source == ZipEntrySource.ZipOutputStream)
                    {
                    }
                    else
                    {
                        //input = File.OpenRead(LocalFileName);
                        input = File.Open(LocalFileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
                    }

                    var crc32 = new Crisis.Ionic.Crc.CRC32();
                    _Crc32 = crc32.GetCrc32(input);

                    if (_sourceStream == null)
                    {
#if NETCF
                        input.Close();
#else
                        input.Dispose();
#endif
                    }
                }
                _crcCalculated = true;
            }
            return _Crc32;
        }