vm: fail if ROT has not enough arguments

pkg/vm/vm.go

@@ -388,13 +388,11 @@ func (v *VM) execute(ctx *Context, op Instruction) {
 		v.estack.InsertAt(a, n)
 
 	case ROT:
-		c := v.estack.Pop()
-		b := v.estack.Pop()
-		a := v.estack.Pop()
-
-		v.estack.Push(b)
-		v.estack.Push(c)
-		v.estack.Push(a)
+		e := v.estack.RemoveAt(2)
+		if e == nil {
+			panic("no top-level element found")
+		}
+		v.estack.Push(e)
 
 	case DEPTH:
 		v.estack.PushVal(v.estack.Len())

pkg/vm/vm_test.go

@@ -659,6 +659,29 @@ func TestPICKgood(t *testing.T) {
 	assert.Equal(t, int64(result), vm.estack.Pop().BigInt().Int64())
 }
 
+func TestROTBad(t *testing.T) {
+	prog := makeProgram(ROT)
+	vm := load(prog)
+	vm.estack.PushVal(1)
+	vm.estack.PushVal(2)
+	vm.Run()
+	assert.Equal(t, true, vm.state.HasFlag(faultState))
+}
+
+func TestROTGood(t *testing.T) {
+	prog := makeProgram(ROT)
+	vm := load(prog)
+	vm.estack.PushVal(1)
+	vm.estack.PushVal(2)
+	vm.estack.PushVal(3)
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 3, vm.estack.Len())
+	assert.Equal(t, makeStackItem(1), vm.estack.Pop().value)
+	assert.Equal(t, makeStackItem(3), vm.estack.Pop().value)
+	assert.Equal(t, makeStackItem(2), vm.estack.Pop().value)
+}
+
 func TestXTUCKbadNoitem(t *testing.T) {
 	prog := makeProgram(XTUCK)
 	vm := load(prog)