Fix calculation when no power in support

gpbft/gpbft.go

@@ -701,7 +701,7 @@ func (i *instance) tryPrepare() error {
 	proposalKey := i.proposal.Key()
 	foundQuorum := prepared.HasStrongQuorumFor(proposalKey)
 	timedOut := atOrAfter(i.participant.host.Time(), i.phaseTimeout) && prepared.ReceivedFromStrongQuorum()
-	quorumNotPossible := !prepared.mayHaveStrongQuorumFor(proposalKey)
+	quorumNotPossible := !prepared.couldReachStrongQuorumFor(proposalKey)
 
 	if foundQuorum {
 		i.value = i.proposal
@@ -1087,22 +1087,19 @@ func (q *quorumState) HasStrongQuorumFor(key ChainKey) bool {
 	return ok && supportForChain.hasStrongQuorum
 }
 
-// mayHaveStrongQuorumFor checks whether the given chain can possibly reach
+// couldReachStrongQuorumFor checks whether the given chain can possibly reach
 // strong quorum.
-func (q *quorumState) mayHaveStrongQuorumFor(key ChainKey) bool {
-	supportForChain, found := q.chainSupport[key]
-	if !found {
-		// There is no support for given chain. Strong quorum is only possible if the
-		// aggregate power of voted participants dos not exceed ⅔ of total power.
-		return !q.ReceivedFromStrongQuorum()
+func (q *quorumState) couldReachStrongQuorumFor(key ChainKey) bool {
+	supportingPower := new(big.Int)
+	if supportForChain, found := q.chainSupport[key]; found {
+		supportingPower.Set(supportForChain.power)
 	}
-
 	// A strong quorum is only feasible when the total support for the given chain,
 	// combined with the aggregate power of not yet voted participants, exceeds ⅔ of
 	// total power.
-	nonSendersTotalPower := NewStoragePower(0).Sub(q.powerTable.Total, q.sendersTotalPower)
-	strongQuorumThreshold := NewStoragePower(0).Add(nonSendersTotalPower, supportForChain.power)
-	return IsStrongQuorum(strongQuorumThreshold, q.powerTable.Total)
+	unvotedPower := NewStoragePower(0).Sub(q.powerTable.Total, q.sendersTotalPower)
+	possibleSupport := NewStoragePower(0).Add(supportingPower, unvotedPower)
+	return IsStrongQuorum(possibleSupport, q.powerTable.Total)
 }
 
 type QuorumResult struct {