Restrict global and function references to memory size

vm/state.go

@@ -2,6 +2,8 @@ package vm
 
 import "fmt"
 
+const GlobalMemorySize = 16
+
 type State struct {
 	running bool
 	err     error
@@ -18,7 +20,7 @@ type State struct {
 func NewState(prog *Program) (*State, error) {
 	return &State{
 		program:      prog,
-		globalMemory: NewMemory(16),
+		globalMemory: NewMemory(GlobalMemorySize),
 	}, nil
 }