Restrict global and function references to memory size

vm/stackframe.go

@@ -1,5 +1,7 @@
 package vm
 
+const FunctionMemorySize = 16
+
 type stackFrame struct {
 	previousFunctionIndex    int64
 	previousInstructionIndex int64
@@ -10,6 +12,6 @@ func newStackFrame(state *State) *stackFrame {
 	return &stackFrame{
 		previousFunctionIndex:    state.functionIndex,
 		previousInstructionIndex: state.instructionIndex,
-		functionMemory:           NewMemory(16),
+		functionMemory:           NewMemory(FunctionMemorySize),
 	}
 }

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
 }