vm: implement the NZ opcode

pkg/vm/vm.go

@@ -499,8 +499,8 @@ func (v *VM) execute(ctx *Context, op Instruction) {
 		v.estack.PushVal(!x)
 
 	case NZ:
-		panic("todo NZ")
-		// x := v.estack.Pop().BigInt()
+		x := v.estack.Pop().BigInt()
+		v.estack.PushVal(x.Cmp(big.NewInt(0)) != 0)
 
 	// Object operations.
 	case NEWARRAY:

pkg/vm/vm_test.go

@@ -231,6 +231,24 @@ func TestSimpleCall(t *testing.T) {
 	assert.Equal(t, result, int(vm.estack.Pop().BigInt().Int64()))
 }
 
+func TestNZtrue(t *testing.T) {
+	prog := makeProgram(NZ)
+	vm := load(prog)
+	vm.estack.PushVal(1)
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, true, vm.estack.Pop().Bool())
+}
+
+func TestNZfalse(t *testing.T) {
+	prog := makeProgram(NZ)
+	vm := load(prog)
+	vm.estack.PushVal(0)
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, false, vm.estack.Pop().Bool())
+}
+
 func makeProgram(opcodes ...Instruction) []byte {
 	prog := make([]byte, len(opcodes)+1) // RET
 	for i := 0; i < len(opcodes); i++ {