fun readInt(
        firstByte: Int,
        prefixMask: Int,
      ): Int {
        val prefix = firstByte and prefixMask
        if (prefix < prefixMask) {
          return prefix // This was a single byte value.
        }

        // This is a multibyte value. Read 7 bits at a time.
        var result = prefixMask
        var shift = 0
        while (true) {
          val b = readByte()