Microsoft.JScript.GlobalObject.Decode C# (CSharp) Method

      private static String Decode(Object encodedURI, URISetType flags){
        String encodedURIStr = Convert.ToString(encodedURI);
        StringBuilder resultStr = new StringBuilder();
        for (int i = 0; i < encodedURIStr.Length; i++){
          char ch = encodedURIStr[i];
          if (ch != '%')
            resultStr.Append(ch);
          else{
            int start = i;
            if (i+2 >= encodedURIStr.Length)
              throw new JScriptException(JSError.URIDecodeError);
            byte b = HexValue(encodedURIStr[i+1], encodedURIStr[i+2]);
            i += 2;

            char ch1;
            if ((b & 0x80) == 0)
              ch1 = (char)b;
            else{
              int n;
              for (n = 1; ((b << n) & 0x80) != 0; n++) ;
              if (n == 1 || n > 4 || i + (n-1) * 3 >= encodedURIStr.Length)
                throw new JScriptException(JSError.URIDecodeError);
              int value = (int)b & 0xFF >> (n+1);
              for (; n > 1; n--){
                if (encodedURIStr[i+1] != '%')
                  throw new JScriptException(JSError.URIDecodeError);
                b = HexValue(encodedURIStr[i+2], encodedURIStr[i+3]);
                i += 3;
                // The two leading bits should be 10 for a valid UTF-8 encoding.
                if ((b & 0xC0) != 0x80)
                  throw new JScriptException(JSError.URIDecodeError);
                value = value << 6 | (int)(b & 0x3F);
              }
              if (value >= 0xD800 && value < 0xE000)
                throw new JScriptException(JSError.URIDecodeError);
              if (value < 0x10000)
                ch1 = (char)value;
              else{
                if (value > 0x10FFFF)
                  throw new JScriptException(JSError.URIDecodeError);
                resultStr.Append((char)((value - 0x10000 >> 10 & 0x3FF) + 0xD800));
                resultStr.Append((char)((value - 0x10000       & 0x3FF) + 0xDC00));
                continue;
              }
            }

            if (GlobalObject.InURISet(ch1, flags))
              resultStr.Append(encodedURIStr, start, i-start+1);
            else
              resultStr.Append(ch1);
          }
        }

        return resultStr.ToString();
      }