Asp.net Convert a title to a FriendlyUrl

//http://stackoverflow.com/questions/25259/how-does-stack-overflow-generate-its-seo-friendly-urls/25063322#25063322

public static string ToFriendlyUrl(string title, bool utf8 = false, int maxlen=80)
{
    if (title == null) return "";

    int len = title.Length;
    bool prevdash = false;
    var sb = new StringBuilder(len);
    char c;

    for (int i = 0; i < len; i++)
    {
        c = title[i];
        if ((c >= 'a' && c <= 'z') || (c >= '0' && c <= '9'))
        {
            sb.Append(c);
            prevdash = false;
        }
        else if (c >= 'A' && c <= 'Z')
        {
            // tricky way to convert to lowercase
            sb.Append((char)(c | 32));
            prevdash = false;
        }
        else if (c == ' ' || c == ',' || c == '.' || c == '/' ||
            c == '\\' || c == '-' || c == '_' || c == '=')
        {
            if (!prevdash && sb.Length > 0)
            {
                sb.Append('-');
                prevdash = true;
            }
        }
        else if (c >= 128)
        {
            int prevlen = sb.Length;
            if (utf8)
            {
                sb.Append(HttpUtility.UrlEncode(c.ToString(CultureInfo.InvariantCulture),Encoding.UTF8));
            }
            else
            {
                //http://meta.stackexchange.com/questions/7435/non-us-ascii-characters-dropped-from-full-profile-url/7696#7696
                sb.Append(RemapInternationalCharToAscii(c));
            }

            if (prevlen != sb.Length) prevdash = false;
        }
        if (i == maxlen) break;
    }

    if (prevdash)
        return sb.ToString().Substring(0, sb.Length - 1);
    else
        return sb.ToString();
}