[Scummvm-cvs-logs] SF.net SVN: scummvm: [25614] scummvm/trunk/engines/parallaction/commands. cpp

[peres001 at users.sourceforge.net]

Revision: 25614
          http://scummvm.svn.sourceforge.net/scummvm/?rev=25614&view=rev
Author:   peres001
Date:     2007-02-15 13:43:56 -0800 (Thu, 15 Feb 2007)

Log Message:
-----------
fixed a bug in the original engine causing memory-protected systems to occasionally crash

Modified Paths:
--------------
    scummvm/trunk/engines/parallaction/commands.cpp

Modified: scummvm/trunk/engines/parallaction/commands.cpp
===================================================================
--- scummvm/trunk/engines/parallaction/commands.cpp	2007-02-15 21:42:57 UTC (rev 25613)
+++ scummvm/trunk/engines/parallaction/commands.cpp	2007-02-15 21:43:56 UTC (rev 25614)
@@ -295,11 +295,19 @@
 			break;
 
 		case CMD_ON:	// on
-			u->_zone->_flags &= ~kFlagsRemove;
-			u->_zone->_flags |= kFlagsActive;
-			if ((u->_zone->_type & 0xFFFF) == kZoneGet) {
-				addJob(&jobDisplayDroppedItem, u->_zone, kPriority17 );
-			}
+            // WORKAROUND: the original DOS-based engine didn't check u->_zone before dereferencing
+            // the pointer to get structure members, thus leading to crashes in systems with memory
+            // protection.
+            // As a side note, the overwritten address is the 5th entry in the DOS interrupt table
+            // (print screen handler): this suggests that a system would hang when the print screen
+            // key is pressed after playing Nippon Safes, provided that this code path is taken.
+            if (u->_zone != NULL) {
+                u->_zone->_flags &= ~kFlagsRemove;
+                u->_zone->_flags |= kFlagsActive;
+                if ((u->_zone->_type & 0xFFFF) == kZoneGet) {
+                    addJob(&jobDisplayDroppedItem, u->_zone, kPriority17 );
+                }
+            }
 			break;
 
 		case CMD_OFF:	// off


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