System.Xml.XmlTextReaderImpl.DetectEncoding C# (CSharp) Méthode

        private Encoding DetectEncoding()
        {
            Debug.Assert(_ps.bytes != null);
            Debug.Assert(_ps.bytePos == 0);

            if (_ps.bytesUsed < 2)
            {
                return null;
            }
            int first2Bytes = _ps.bytes[0] << 8 | _ps.bytes[1];
            int next2Bytes = (_ps.bytesUsed >= 4) ? (_ps.bytes[2] << 8 | _ps.bytes[3]) : 0;

            switch (first2Bytes)
            {
				// Removing USC4 encoding
                case 0x0000:
                    switch (next2Bytes)
                    {
                        case 0xFEFF:
                            return Ucs4Encoding.UCS4_Bigendian;
                        case 0x003C:
                            return Ucs4Encoding.UCS4_Bigendian;
                        case 0xFFFE:
                            return Ucs4Encoding.UCS4_2143;
                        case 0x3C00:
                            return Ucs4Encoding.UCS4_2143;
                    }
                    break;
                case 0xFEFF:
                    if (next2Bytes == 0x0000)
                    {
                        return Ucs4Encoding.UCS4_3412;
                    }
                    else
                    {
                        return Encoding.BigEndianUnicode;
                    }
                case 0xFFFE:
                    if (next2Bytes == 0x0000)
                    {
                        return Ucs4Encoding.UCS4_Littleendian;
                    }
                    else
                    {
                        return Encoding.Unicode;
                    }
                case 0x3C00:
                    if (next2Bytes == 0x0000)
                    {
                        return Ucs4Encoding.UCS4_Littleendian;
                    }
                    else
                    {
                        return Encoding.Unicode;
                    }
                case 0x003C:
                    if (next2Bytes == 0x0000)
                    {
                        return Ucs4Encoding.UCS4_3412;
                    }
                    else
                    {
                        return Encoding.BigEndianUnicode;
                    }
                case 0x4C6F:
                    if (next2Bytes == 0xA794)
                    {
                        Throw(SR.Xml_UnknownEncoding, "ebcdic");
                    }
                    break;
                case 0xEFBB:
                    if ((next2Bytes & 0xFF00) == 0xBF00)
                    {
                        return new UTF8Encoding(true, true);
                    }
                    break;
            }
            // Default encoding is ASCII (using SafeAsciiDecoder) until we read xml declaration. 
            // If we set UTF8 encoding now, it will throw exceptions (=slow) when decoding non-UTF8-friendly 
            // characters after the xml declaration, which may be perfectly valid in the encoding 
            // specified in xml declaration.
            return null;
        }