vm: do nothing if SHL/SHR by 0

pkg/vm/vm.go

@@ -505,11 +505,17 @@ func (v *VM) execute(ctx *Context, op Instruction) {
 
 	case SHL:
 		b := v.estack.Pop().BigInt()
+		if b.Int64() == 0 {
+			return
+		}
 		a := v.estack.Pop().BigInt()
 		v.estack.PushVal(new(big.Int).Lsh(a, uint(b.Int64())))
 
 	case SHR:
 		b := v.estack.Pop().BigInt()
+		if b.Int64() == 0 {
+			return
+		}
 		a := v.estack.Pop().BigInt()
 		v.estack.PushVal(new(big.Int).Rsh(a, uint(b.Int64())))
 

pkg/vm/vm_test.go

@@ -283,6 +283,50 @@ func TestSub(t *testing.T) {
 	assert.Equal(t, int64(2), vm.estack.Pop().BigInt().Int64())
 }
 
+func TestSHRGood(t *testing.T) {
+	prog := makeProgram(SHR)
+	vm := load(prog)
+	vm.estack.PushVal(4)
+	vm.estack.PushVal(2)
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 1, vm.estack.Len())
+	assert.Equal(t, makeStackItem(1), vm.estack.Pop().value)
+}
+
+func TestSHRZero(t *testing.T) {
+	prog := makeProgram(SHR)
+	vm := load(prog)
+	vm.estack.PushVal([]byte{0, 1})
+	vm.estack.PushVal(0)
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 1, vm.estack.Len())
+	assert.Equal(t, makeStackItem([]byte{0, 1}), vm.estack.Pop().value)
+}
+
+func TestSHLGood(t *testing.T) {
+	prog := makeProgram(SHL)
+	vm := load(prog)
+	vm.estack.PushVal(4)
+	vm.estack.PushVal(2)
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 1, vm.estack.Len())
+	assert.Equal(t, makeStackItem(16), vm.estack.Pop().value)
+}
+
+func TestSHLZero(t *testing.T) {
+	prog := makeProgram(SHL)
+	vm := load(prog)
+	vm.estack.PushVal([]byte{0, 1})
+	vm.estack.PushVal(0)
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 1, vm.estack.Len())
+	assert.Equal(t, makeStackItem([]byte{0, 1}), vm.estack.Pop().value)
+}
+
 func TestLT(t *testing.T) {
 	prog := makeProgram(LT)
 	vm := load(prog)