🚸 Fix G4 Dwell overflow

Author: TBAMax

Marlin/src/core/millis_t.h

@@ -30,5 +30,8 @@ typedef uint32_t millis_t;
 #define MS_TO_SEC(N) millis_t((N)/1000UL)
 #define MS_TO_SEC_PRECISE(N) (float(N)/1000.0f)
 
-#define PENDING(NOW,SOON) ((int32_t)(NOW-(SOON))<0)
+#define FUTURE(START,DURA) (millis_t(millis()-(START))<(DURA))
+#define PAST(START,DURA) (!FUTURE(START,DURA))
+
+#define PENDING(NOW,SOON) (int32_t((NOW)-(SOON))<0)
 #define ELAPSED(NOW,SOON) (!PENDING(NOW,SOON))

Marlin/src/gcode/gcode.cpp

@@ -242,11 +242,11 @@ void GcodeSuite::get_destination_from_command() {
 }
 
 /**
- * Dwell waits immediately. It does not synchronize. Use M400 instead of G4
+ * Dwell waits immediately. It does not synchronize.
  */
-void GcodeSuite::dwell(millis_t time) {
-  time += millis();
-  while (PENDING(millis(), time)) idle();
+void GcodeSuite::dwell(const millis_t time) {
+  const millis_t startMillis = millis();
+  while (FUTURE(startMillis, time)) idle();
 }
 
 /**

Marlin/src/gcode/gcode.h

@@ -503,7 +503,7 @@ class GcodeSuite {
     #define KEEPALIVE_STATE(N) NOOP
   #endif
 
-  static void dwell(millis_t time);
+  static void dwell(const millis_t time);
 
 private: