Lucene.Net.QueryParsers.QueryParser.DiscardEscapeChar C# (CSharp) Method

        private String DiscardEscapeChar(String input)
        {
            // Create char array to hold unescaped char sequence
            char[] output = new char[input.Length];

            // The Length of the output can be less than the input
            // due to discarded escape chars. This variable holds
            // the actual Length of the output
            int Length = 0;

            // We remember whether the last processed character was 
            // an escape character
            bool lastCharWasEscapeChar = false;

            // The multiplier the current unicode digit must be multiplied with.
            // E. g. the first digit must be multiplied with 16^3, the second with 16^2...
            int codePointMultiplier = 0;

            // Used to calculate the codepoint of the escaped unicode character
            int codePoint = 0;

            for (int i = 0; i < input.Length; i++)
            {
                char curChar = input[i];
                if (codePointMultiplier > 0)
                {
                    codePoint += HexToInt(curChar) * codePointMultiplier;
                    codePointMultiplier = Number.URShift(codePointMultiplier, 4);
                    if (codePointMultiplier == 0)
                    {
                        output[Length++] = (char)codePoint;
                        codePoint = 0;
                    }
                }
                else if (lastCharWasEscapeChar)
                {
                    if (curChar == 'u')
                    {
                        // found an escaped unicode character
                        codePointMultiplier = 16 * 16 * 16;
                    }
                    else
                    {
                        // this character was escaped
                        output[Length] = curChar;
                        Length++;
                    }
                    lastCharWasEscapeChar = false;
                }
                else
                {
                    if (curChar == '\\')
                    {
                        lastCharWasEscapeChar = true;
                    }
                    else
                    {
                        output[Length] = curChar;
                        Length++;
                    }
                }
            }

            if (codePointMultiplier > 0)
            {
                throw new ParseException("Truncated unicode escape sequence.");
            }

            if (lastCharWasEscapeChar)
            {
                throw new ParseException("Term can not end with escape character.");
            }

            return new String(output, 0, Length);
        }