add stop song effect! finally!

src/engine/engine.cpp

@@ -1458,7 +1458,7 @@ const char* DivEngine::getEffectDesc(unsigned char effect, int chan) {
     case 0xef:
       return "EFxx: Set global tuning (quirky!)";
     case 0xff:
-      return "FFxx: Stop song (not implemented yet)";
+      return "FFxx: Stop song";
     default:
       if (chan>=0 && chan<chans) {
         const char* ret=disCont[dispatchOfChan[chan]].dispatch->getEffectName(effect);

src/engine/playback.cpp

@@ -738,7 +738,15 @@ void DivEngine::processRow(int i, bool afterDelay) {
       case 0xef: // global pitch
         globalPitch+=(signed char)(effectVal-0x80);
         break;
-      case 0xff: // stop song TODO
+      case 0xff: // stop song
+        freelance=false;
+        playing=false;
+        extValuePresent=false;
+        stepPlay=0;
+        remainingLoops=-1;
+        sPreview.sample=-1;
+        sPreview.wave=-1;
+        sPreview.pos=0;
         break;
     }
   }