[#63] Fix threshold number calculation

`x*2/3` is not equal to `x/3*2` with integers.
The only correct way to calculate threshold is
the first one.

Signed-off-by: Alex Vanin <[email protected]>

common/ir.go

@@ -48,7 +48,7 @@ func AlphabetAddress() []byte {
 // Multiaddress returns default multi signature account address for N keys.
 // If committee set to true, then it is `M = N/2+1` committee account.
 func Multiaddress(n []interop.PublicKey, committee bool) []byte {
-	threshold := len(n)/3*2 + 1
+	threshold := len(n)*2/3 + 1
 	if committee {
 		threshold = len(n)/2 + 1
 	}

neofs/neofs_contract.go

@@ -144,7 +144,7 @@ func InnerRingCandidateRemove(key interop.PublicKey) bool {
 
 	if !runtime.CheckWitness(key) {
 		alphabet := getNodes(ctx, alphabetKey)
-		threshold := len(alphabet)/3*2 + 1
+		threshold := len(alphabet)*2/3 + 1
 
 		nodeKey := common.InnerRingInvoker(alphabet)
 		if len(nodeKey) == 0 {
@@ -286,7 +286,7 @@ func Withdraw(user []byte, amount int) bool {
 func Cheque(id []byte, user interop.Hash160, amount int, lockAcc []byte) bool {
 	ctx := storage.GetContext()
 	alphabet := getNodes(ctx, alphabetKey)
-	threshold := len(alphabet)/3*2 + 1
+	threshold := len(alphabet)*2/3 + 1
 
 	cashedCheques := getCashedCheques(ctx)
 	hashID := crypto.Sha256(id)
@@ -369,7 +369,7 @@ func AlphabetUpdate(chequeID []byte, args []interop.PublicKey) bool {
 	}
 
 	alphabet := getNodes(ctx, alphabetKey)
-	threshold := len(alphabet)/3*2 + 1
+	threshold := len(alphabet)*2/3 + 1
 
 	key := common.InnerRingInvoker(alphabet)
 	if len(key) == 0 {
@@ -426,7 +426,7 @@ func SetConfig(id, key, val []byte) bool {
 
 	// check if it is alphabet invocation
 	alphabet := getNodes(ctx, alphabetKey)
-	threshold := len(alphabet)/3*2 + 1
+	threshold := len(alphabet)*2/3 + 1
 
 	nodeKey := common.InnerRingInvoker(alphabet)
 	if len(nodeKey) == 0 {