
      var value = inverseAlphabet[char];
      if (value &gt;= 0) {
        char = alphabet.codeUnitAt(value);
        if (char == originalChar) continue;
      } else if (value == _Base64Decoder._padding) {
        &#47;&#47; We have ruled out percent, so char is &#39;=&#39;.
        if (firstPadding &lt; 0) {
          &#47;&#47; Mark position in normalized output where padding occurs.
          firstPadding = (buffer?.length ?? 0) + (sliceEnd - sliceStart);
          firstPaddingSourceIndex = sliceEnd;
