Javadoc
Returns a message digest: for each member P the highest seqno received from P without a gap is added to
the digest. E.g. if the seqnos received from P are [+3 +4 +5 -6 +7 +8], then 5 will be returned. Also, the
highest seqno seen is added. The max of all highest seqnos seen will be used (in STABLE) to determine
whether the last seqno from a sender was received (see "Last Message Dropped" topic in DESIGN).