Add SUB Opcode

pkg/vm/vm_ops.go

@@ -4,4 +4,5 @@ import "github.com/CityOfZion/neo-go/pkg/vm/stack"
 
 var opFunc = map[stack.Instruction]func(ctx *stack.Context, istack *stack.Invocation) error{
 	stack.ADD: Add,
+	stack.SUB: Sub,
 }

pkg/vm/vm_ops_maths_test.go

@@ -37,3 +37,33 @@ func TestAddOp(t *testing.T) {
 	assert.Equal(t, int64(43), item.Value().Int64())
 
 }
+
+func TestSubOp(t *testing.T) {
+
+	v := VM{}
+
+	a, err := stack.NewInt(big.NewInt(30))
+	if err != nil {
+		t.Fail()
+	}
+	b, err := stack.NewInt(big.NewInt(40))
+	if err != nil {
+		t.Fail()
+	}
+
+	ctx := stack.NewContext([]byte{})
+	ctx.Estack.Push(a).Push(b)
+
+	v.ExecuteOp(stack.SUB, 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(-10), item.Value().Int64())
+
+}