improve timeout loops for millis() rollover

Author: sandeepmistry

src/GSMPIN.cpp

@@ -35,7 +35,7 @@ int GSMPIN::isPIN()
 {
   String response;
 
-  for (unsigned long start = millis(); millis() < (start + 1000);) {
+  for (unsigned long start = millis(); (millis() - start) < 1000;) {
     MODEM.send("AT+CPIN?");
 
     if (MODEM.waitForResponse(10000, &response) == 1) {
@@ -124,7 +124,7 @@ void GSMPIN::switchPIN(String pin)
 
 int GSMPIN::checkReg()
 {
-  for (unsigned long start = millis(); millis() < (start + 10000L);) {
+  for (unsigned long start = millis(); (millis() - start) < 10000L;) {
     MODEM.send("AT+CREG?");
 
     String response = "";

src/GSMVoiceCall.cpp

@@ -63,7 +63,7 @@ int GSMVoiceCall::voiceCall(const char* to, unsigned long timeout)
     }
 
     _callStatus = CALLING;
-    for (unsigned long start = millis(); (timeout == 0) || (millis() < (start + timeout));) {
+    for (unsigned long start = millis(); (timeout == 0) || ((millis() - start) < timeout);) {
       if (getvoiceCallStatus() != CALLING) {
         break;
       }

src/Modem.cpp

@@ -103,7 +103,7 @@ void ModemClass::debug()
 
 int ModemClass::autosense(int timeout)
 {
-  for (unsigned long start = millis(); millis() < (start + timeout);) {
+  for (unsigned long start = millis(); (millis() - start) < timeout;) {
     if (noop() == 1) {
       return 1;
     }
@@ -186,7 +186,7 @@ void ModemClass::sendf(const char *fmt, ...)
 int ModemClass::waitForResponse(unsigned long timeout, String* responseDataStorage)
 {
   _responseDataStorage = responseDataStorage;
-  for (unsigned long start = millis(); millis() < (start + timeout);) {
+  for (unsigned long start = millis(); (millis() - start) < timeout;) {
     int r = ready();
 
     if (r != 0) {