VM: Implemented SIGN, NEGATE opcode (#232)

* Implemented SIGN, NEGATE opcode

pkg/vm/vm_ops.go

@@ -7,6 +7,8 @@ type stackInfo func(op stack.Instruction, ctx *stack.Context, istack *stack.Invo
 var opFunc = map[stack.Instruction]stackInfo{
 	stack.INC:         Inc,
 	stack.DEC:         Dec,
+	stack.SIGN:        Sign,
+	stack.NEGATE:      Negate,
 	stack.ADD:         Add,
 	stack.SUB:         Sub,
 	stack.PUSHBYTES1:  PushNBytes,

pkg/vm/vm_ops_maths.go

@@ -46,7 +46,7 @@ func Sub(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rst
 
 // 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
+// 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()
@@ -71,7 +71,7 @@ func Inc(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rst
 
 // 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
+// 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()
@@ -94,6 +94,47 @@ func Dec(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rst
 	return NONE, nil
 }
 
+// Sign puts the sign of the top stack Item on top of the stack.
+// If value is negative, put -1;
+// If positive, put 1;
+// If value is zero, put 0.
+func Sign(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
+	}
+
+	s := int64(i.Value().Sign())
+	sign, err := stack.NewInt(big.NewInt(s))
+	if err != nil {
+		return FAULT, err
+	}
+
+	ctx.Estack.Push(sign)
+
+	return NONE, nil
+}
+
+// Negate flips the sign of the stack Item.
+func Negate(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
+	}
+
+	a := big.NewInt(0).Neg(i.Value())
+	b, err := stack.NewInt(a)
+	if err != nil {
+		return FAULT, err
+	}
+
+	ctx.Estack.Push(b)
+
+	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

@@ -117,3 +117,53 @@ func TestSubOp(t *testing.T) {
 	assert.Equal(t, int64(-10), item.Value().Int64())
 
 }
+
+func TestSignOp(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.SIGN, 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(-1), item.Value().Int64())
+}
+
+func TestNegateOp(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.NEGATE, 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(20), item.Value().Int64())
+}