fix #362: Fix skipping of "repeat zero times" loops

Author: adazem009

src/engine/virtualmachine_p.cpp

@@ -264,8 +264,15 @@ unsigned int *VirtualMachinePrivate::run(unsigned int *pos, bool reset)
     FREE_REGS(1);
     if (loopCount <= 0) {
         loopEnd = pos;
-        while (*loopEnd != OP_LOOP_END)
+        unsigned int loopCounter = 1;
+        while ((*loopEnd != OP_LOOP_END) || (loopCounter > 0)) {
             loopEnd += instruction_arg_count[*loopEnd++];
+
+            if ((*loopEnd == OP_FOREVER_LOOP) || (*loopEnd == OP_REPEAT_LOOP) || (*loopEnd == OP_UNTIL_LOOP))
+                loopCounter++;
+            else if (*loopEnd == OP_LOOP_END)
+                loopCounter--;
+        }
         pos = loopEnd;
     } else {
         Loop l;
@@ -313,6 +320,7 @@ do_repeat_loop_index1 : {
     return pos;
 
 do_loop_end : {
+    assert(!loops.empty());
     Loop &l = loops.back();
     if (l.isRepeatLoop) {
         if ((l.index == -1) || (++l.index < l.max))

test/virtual_machine/virtual_machine_test.cpp

@@ -1602,3 +1602,17 @@ TEST(VirtualMachineTest, Reset)
     vm.reset();
     ASSERT_FALSE(vm.atEnd());
 }
+
+TEST(VirtualMachineTest, NoCrashWhenRepeatingZeroTimes)
+{
+    // Regtest for #362
+    static unsigned int bytecode[] = { OP_START, OP_CONST, 0, OP_REPEAT_LOOP, OP_UNTIL_LOOP, OP_NULL, OP_BEGIN_UNTIL_LOOP, OP_LOOP_END, OP_LOOP_END, OP_HALT };
+    static Value constValues[] = { 0 };
+
+    EngineMock engineMock;
+    VirtualMachine vm(nullptr, &engineMock, nullptr);
+    vm.setBytecode(bytecode);
+    vm.setConstValues(constValues);
+    vm.run();
+    ASSERT_EQ(vm.registerCount(), 0);
+}