System.Xml.Base64Decoder.Decode C# (CSharp) Method

        private unsafe void Decode( char* pChars, char* pCharsEndPos, 
                             byte* pBytes, byte* pBytesEndPos, 
                             out int charsDecoded, out int bytesDecoded ) {
#if DEBUG
            Debug.Assert( pCharsEndPos - pChars >= 0 );
            Debug.Assert( pBytesEndPos - pBytes >= 0 );
#endif

            // walk hex digits pairing them up and shoving the value of each pair into a byte
            byte *pByte = pBytes;
            char *pChar = pChars;
            int b = bits;
            int bFilled = bitsFilled;
            XmlCharType xmlCharType = XmlCharType.Instance;
            while ( pChar < pCharsEndPos && pByte < pBytesEndPos ) {
                char ch = *pChar;
                // end?
                if ( ch == '=' ) { 
                    break;
                }
                pChar++;

                // ignore white space
                if ( ( xmlCharType.charProperties[ch] & XmlCharType.fWhitespace ) != 0 ) {  // if ( xmlCharType.IsWhiteSpace(ch) ) {
                    continue;
                }

                int digit;
                if ( ch > 122 || ( digit = MapBase64[ch] ) == Invalid ) {
                    throw new XmlException(Res.Xml_InvalidBase64Value, new string( pChars, 0, (int)(pCharsEndPos - pChars) ));
                }

                b = ( b << 6 ) | digit;
                bFilled += 6;

                if ( bFilled >= 8 ) {
                    // get top eight valid bits
                    *pByte++ = (byte)( ( b >> ( bFilled - 8 ) ) & 0xFF ); 
                    bFilled -= 8;

                    if ( pByte == pBytesEndPos ) {
                        goto Return;
                    }
                }
            }

            if ( pChar < pCharsEndPos && *pChar == '=' ) {
                bFilled = 0;
                // ignore padding chars
                do {
                    pChar++;
                } while ( pChar < pCharsEndPos && *pChar == '=' );

                // ignore whitespace after the padding chars
                if ( pChar < pCharsEndPos ) {
                    do {
                        if ( !( ( xmlCharType.charProperties[*pChar++] & XmlCharType.fWhitespace ) != 0 ) ) {  // if ( !( xmlCharType.IsWhiteSpace( chars[charPos++] ) ) ) {
                            throw new XmlException(Res.Xml_InvalidBase64Value, new string( pChars, 0, (int)( pCharsEndPos - pChars ) ));
                        }
                    } while ( pChar < pCharsEndPos );
                }
            }

        Return:
            bits = b;
            bitsFilled = bFilled;

            bytesDecoded = (int)(pByte - pBytes);
            charsDecoded = (int)(pChar - pChars);
        }
    }