Add popTwoIntegers convenience func

pkg/vm/vm_ops_maths.go

@@ -1,19 +1,16 @@
 package vm
 
-import "github.com/CityOfZion/neo-go/pkg/vm/stack"
+import (
+	"github.com/CityOfZion/neo-go/pkg/vm/stack"
+)
 
 // Add adds two stack Items together.
 // Returns an error if either items cannot be casted to an integer
 // or if integers cannot be added together
 func Add(ctx *stack.Context, istack *stack.Invocation) error {
-	operandA, err := ctx.Estack.PopInt()
-	if err != nil {
-		return err
-	}
-	operandB, err := ctx.Estack.PopInt()
-	if err != nil {
-		return err
-	}
+
+	operandA, operandB, err := popTwoIntegers(ctx)
+
 	res, err := operandA.Add(operandB)
 	if err != nil {
 		return err
@@ -23,3 +20,33 @@ func Add(ctx *stack.Context, istack *stack.Invocation) error {
 
 	return nil
 }
+
+// Sub subtracts two stack Items.
+// Returns an error if either items cannot be casted to an integer
+// or if integers cannot be subtracted together
+func Sub(ctx *stack.Context, istack *stack.Invocation) error {
+
+	operandA, operandB, err := popTwoIntegers(ctx)
+
+	res, err := operandB.Sub(operandA)
+	if err != nil {
+		return err
+	}
+
+	ctx.Estack.Push(res)
+
+	return nil
+}
+
+func popTwoIntegers(ctx *stack.Context) (*stack.Int, *stack.Int, error) {
+	operandA, err := ctx.Estack.PopInt()
+	if err != nil {
+		return nil, nil, err
+	}
+	operandB, err := ctx.Estack.PopInt()
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return operandA, operandB, nil
+}