Potential rounding issues (and updating comments) (#742)

* Update commets
* Update TimeOfRound

Signed-off-by: Kirk Baird <baird.k@outlook.com>
Co-authored-by: Will <will@cypherpunk.email>

chain/time.go

@@ -19,14 +19,17 @@ func TimeOfRound(period time.Duration, genesis int64, round uint64) int64 {
 	if round == 0 {
 		return genesis
 	}
+	if period < 0 {
+		return TimeOfRoundErrorValue
+	}
 
-	periodBits := math.Log2(float64(period))
-	if round > (math.MaxUint64 >> int(periodBits)) {
+	periodBits := math.Log2(float64(period.Seconds()) + 1)  // require x >=1 in log2(x)
+	if round >= (math.MaxUint64 >> (int(periodBits) + 2)) { // +1 for mul overflow, +1 for casting int64
 		return TimeOfRoundErrorValue
 	}
+	// - 1 because genesis time is for 1st round already
 	delta := (round - 1) * uint64(period.Seconds())
 
-	// - 1 because genesis time is for 1st round already
 	val := genesis + int64(delta)
 	if val > math.MaxInt64-maxTimeBuffer {
 		return TimeOfRoundErrorValue

chain/time_test.go

@@ -20,9 +20,19 @@ func TestTimeOverflow(t *testing.T) {
 		t.Fatal("future rounds should not allow previous times.")
 	}
 
-	overflowRound := TimeOfRound(period, start, math.MaxInt64)
-	if overflowRound < smallRound {
-		t.Fatal("future rounds should not allow previous times.")
+	overflowRound := TimeOfRound(period, start, math.MaxUint64 >> 3)
+	if overflowRound != TimeOfRoundErrorValue {
+		t.Fatal("overflow shoud return error.")
+	}
+
+	overflowRound2 := TimeOfRound(period + 2 * time.Second, start, (math.MaxUint64 >> 3) - 1)
+	if overflowRound2 != TimeOfRoundErrorValue {
+		t.Fatal("overflow shoud return error.")
+	}
+
+	negativePeriod := TimeOfRound(-1, start, math.MaxUint64)
+	if negativePeriod != TimeOfRoundErrorValue {
+		t.Fatal("negative period shoud return error.")
 	}
 }
 

net/control.go

@@ -19,7 +19,7 @@ type ControlListener struct {
 	lis   net.Listener
 }
 
-// NewTCPGrpcControlListener registers the pairing between a ControlServer and a grpx server
+// NewTCPGrpcControlListener registers the pairing between a ControlServer and a grpc server
 func NewTCPGrpcControlListener(s control.ControlServer, controlAddr string) ControlListener {
 	lis, err := net.Listen(controlListenAddr(controlAddr))
 	if err != nil {