Add THROWIFNOT Opcode

pkg/vm/vm_ops_exceptions.go

@@ -0,0 +1,33 @@
+package vm
+
+import (
+	"errors"
+
+	"github.com/CityOfZion/neo-go/pkg/vm/stack"
+)
+
+// vm exceptions
+
+// THROWIFNOT faults if the item on the top of the stack
+// does not evaluate to true
+// For specific logic on how a number of bytearray is evaluated can be seen
+// from the boolean conversion methods on the stack items
+func THROWIFNOT(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation) (Vmstate, error) {
+
+	// Pop item from top of stack
+	item, err := ctx.Estack.Pop()
+	if err != nil {
+		return FAULT, err
+	}
+	// Convert to a boolean
+	ok, err := item.Boolean()
+	if err != nil {
+		return FAULT, err
+	}
+
+	// If false, throw
+	if !ok.Value() {
+		return FAULT, errors.New("Item on top of stack evaluates to false")
+	}
+	return NONE, nil
+}