if (limit == -1L && source.exhausted()) return END_OF_DATA

    // Read the tag.
    val tagAndClass = source.readByte().toInt() and 0xff
    val tagClass = tagAndClass and 0b1100_0000
    val constructed = (tagAndClass and 0b0010_0000) == 0b0010_0000
    val tag =
      when (val tag0 = tagAndClass and 0b0001_1111) {
        0b0001_1111 -> readVariableLengthLong()
        else -> tag0.toLong()
      }