System.Net.Http.Headers.StringWithQualityHeaderValue.TryReadQuality C# (CSharp) Method

        private static bool TryReadQuality(string input, StringWithQualityHeaderValue result, ref int index)
        {
            int current = index;

            // See if we have a quality value by looking for "q"
            if ((current == input.Length) || ((input[current] != 'q') && (input[current] != 'Q')))
            {
                return false;
            }

            current++; // skip 'q' identifier
            current = current + HttpRuleParser.GetWhitespaceLength(input, current);

            // If we found "q" it must be followed by "="
            if ((current == input.Length) || (input[current] != '='))
            {
                return false;
            }

            current++; // skip '=' separator
            current = current + HttpRuleParser.GetWhitespaceLength(input, current);

            if (current == input.Length)
            {
                return false;
            }

            int qualityLength = HttpRuleParser.GetNumberLength(input, current, true);

            if (qualityLength == 0)
            {
                return false;
            }

            double quality = 0;
            if (!double.TryParse(input.Substring(current, qualityLength), NumberStyles.AllowDecimalPoint,
                NumberFormatInfo.InvariantInfo, out quality))
            {
                return false;
            }

            if ((quality < 0) || (quality > 1))
            {
                return false;
            }

            result._quality = quality;

            current = current + qualityLength;
            current = current + HttpRuleParser.GetWhitespaceLength(input, current);

            index = current;
            return true;
        }