Use main

include/PSX/jabyengine.h

@@ -4,20 +4,33 @@
 
 namespace JabyEngine {
     struct NextRoutine {
-        typedef NextRoutine (*ExecutionFunction)();
+        static constexpr uintptr_t OverlayBit = (1 << ((sizeof(uintptr_t)*8) - 2));
+        typedef NextRoutine (*MainRoutine)();
 
         uintptr_t value;
 
-        static NextRoutine null() {
+        constexpr static NextRoutine null() {
             return {.value = 0};
         }
 
-        static NextRoutine from(ExecutionFunction function) {
+        static NextRoutine from(MainRoutine function) {
             return {.value = reinterpret_cast<uintptr_t>(function)};
         }
+
+        constexpr bool is_overlay() const {
+            return (this->value & OverlayBit);
+        }
+
+        constexpr bool is_absolute() const {
+            return !NextRoutine::is_overlay();
+        }
+
+        constexpr bool is_null() const {
+            return this->value == 0;
+        }
     };
 
-    typedef NextRoutine::ExecutionFunction ExecutionFunction;
+    typedef NextRoutine::MainRoutine MainRoutine;
 }
 
 #endif //!__JABYENGINE__H__