rce.substring(sliceStart, end));
    if (firstPadding &gt;= 0) {
      &#47;&#47; There was padding in the source. Check that it is valid:
      &#47;&#47; * result length a multiple of four
      &#47;&#47; * one or two padding characters at the end.
      _checkPadding(source, firstPaddingSourceIndex, end, firstPadding,
          paddingCount, buffer.length);
    } else {
      &#47;&#47; Length of last chunk (1-4 chars) in the encoding.
      var endLength = ((buffer.length - 1) % 4) + 1;
      if (endLe