VM: Implement INC, DEC opcode (#231)

[VM]

- Implemented INC, DEC opcode

pkg/vm/vm_ops.go

@@ -5,6 +5,8 @@ import "github.com/CityOfZion/neo-go/pkg/vm/stack"
 type stackInfo func(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rstack *stack.RandomAccess) (Vmstate, error)
 
 var opFunc = map[stack.Instruction]stackInfo{
+	stack.INC:         Inc,
+	stack.DEC:         Dec,
 	stack.ADD:         Add,
 	stack.SUB:         Sub,
 	stack.PUSHBYTES1:  PushNBytes,

pkg/vm/vm_ops_maths.go

@@ -1,6 +1,8 @@
 package vm
 
 import (
+	"math/big"
+
 	"github.com/CityOfZion/neo-go/pkg/vm/stack"
 )
 
@@ -42,6 +44,56 @@ func Sub(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rst
 	return NONE, nil
 }
 
+// Inc increments the stack Item's value by 1.
+// Returns an error if the item cannot be casted to an integer
+// or if 1 cannot be added to the item
+func Inc(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rstack *stack.RandomAccess) (Vmstate, error) {
+
+	i, err := ctx.Estack.PopInt()
+	if err != nil {
+		return FAULT, err
+	}
+
+	one, err := stack.NewInt(big.NewInt(1))
+	if err != nil {
+		return FAULT, err
+	}
+
+	res, err := i.Add(one)
+	if err != nil {
+		return FAULT, err
+	}
+
+	ctx.Estack.Push(res)
+
+	return NONE, nil
+}
+
+// Dec decrements the stack Item's value by 1.
+// Returns an error if the item cannot be casted to an integer
+// or if 1 cannot be subtracted to the item
+func Dec(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rstack *stack.RandomAccess) (Vmstate, error) {
+
+	i, err := ctx.Estack.PopInt()
+	if err != nil {
+		return FAULT, err
+	}
+
+	one, err := stack.NewInt(big.NewInt(1))
+	if err != nil {
+		return FAULT, err
+	}
+
+	res, err := i.Sub(one)
+	if err != nil {
+		return FAULT, err
+	}
+
+	ctx.Estack.Push(res)
+
+	return NONE, nil
+}
+
 func popTwoIntegers(ctx *stack.Context) (*stack.Int, *stack.Int, error) {
 	operandA, err := ctx.Estack.PopInt()
 	if err != nil {

pkg/vm/vm_ops_maths_test.go

@@ -8,6 +8,56 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func TestIncOp(t *testing.T) {
+
+	v := VM{}
+
+	a, err := stack.NewInt(big.NewInt(20))
+	if err != nil {
+		t.Fail()
+	}
+
+	ctx := stack.NewContext([]byte{})
+	ctx.Estack.Push(a)
+
+	v.executeOp(stack.INC, ctx)
+
+	// Stack should have one item
+	assert.Equal(t, 1, ctx.Estack.Len())
+
+	item, err := ctx.Estack.PopInt()
+	if err != nil {
+		t.Fail()
+	}
+
+	assert.Equal(t, int64(21), item.Value().Int64())
+}
+
+func TestDecOp(t *testing.T) {
+
+	v := VM{}
+
+	a, err := stack.NewInt(big.NewInt(20))
+	if err != nil {
+		t.Fail()
+	}
+
+	ctx := stack.NewContext([]byte{})
+	ctx.Estack.Push(a)
+
+	v.executeOp(stack.DEC, ctx)
+
+	// Stack should have one item
+	assert.Equal(t, 1, ctx.Estack.Len())
+
+	item, err := ctx.Estack.PopInt()
+	if err != nil {
+		t.Fail()
+	}
+
+	assert.Equal(t, int64(19), item.Value().Int64())
+}
+
 func TestAddOp(t *testing.T) {
 
 	v := VM{}