System.Xml.Xsl.Runtime.XsltFunctions.NormalizeSpace C# (CSharp) Method

        public static string NormalizeSpace(string value)
        {
            XmlCharType xmlCharType = XmlCharType.Instance;
            StringBuilder sb = null;
            int idx, idxStart = 0, idxSpace = 0;

            for (idx = 0; idx < value.Length; idx++)
            {
                if (xmlCharType.IsWhiteSpace(value[idx]))
                {
                    if (idx == idxStart)
                    {
                        // Previous character was a whitespace character, so discard this character
                        idxStart++;
                    }
                    else if (value[idx] != ' ' || idxSpace == idx)
                    {
                        // Space was previous character or this is a non-space character
                        if (sb == null)
                            sb = new StringBuilder(value.Length);
                        else
                            sb.Append(' ');

                        // Copy non-space characters into string builder
                        if (idxSpace == idx)
                            sb.Append(value, idxStart, idx - idxStart - 1);
                        else
                            sb.Append(value, idxStart, idx - idxStart);

                        idxStart = idx + 1;
                    }
                    else
                    {
                        // Single whitespace character doesn't cause normalization, but mark its position
                        idxSpace = idx + 1;
                    }
                }
            }

            if (sb == null)
            {
                // Check for string that is entirely composed of whitespace
                if (idxStart == idx) return string.Empty;

                // If string does not end with a space, then it must already be normalized
                if (idxStart == 0 && idxSpace != idx) return value;

                sb = new StringBuilder(value.Length);
            }
            else if (idx != idxStart)
            {
                sb.Append(' ');
            }

            // Copy non-space characters into string builder
            if (idxSpace == idx)
                sb.Append(value, idxStart, idx - idxStart - 1);
            else
                sb.Append(value, idxStart, idx - idxStart);

            return sb.ToString();
        }