--- a/aircraft_cmd.c	Thu Jan 27 21:00:05 2005 +0000
+++ b/aircraft_cmd.c	Thu Jan 27 21:18:03 2005 +0000
@@ -161,7 +161,7 @@
 	const AircraftVehicleInfo *avi = AircraftVehInfo(p1);
 	Engine *e;
 
-	if (!(IsEngineBuildable(p1, VEH_Aircraft))) return CMD_ERROR;
+	if (!IsEngineBuildable(p1, VEH_Aircraft)) return CMD_ERROR;
 
 	SET_EXPENSES_TYPE(EXPENSES_NEW_VEHICLES);
 

--- a/engine.c	Thu Jan 27 21:00:05 2005 +0000
+++ b/engine.c	Thu Jan 27 21:18:03 2005 +0000
@@ -906,17 +906,20 @@
 	{ 'ENGS', LoadSave_ENGS, LoadSave_ENGS, CH_RIFF | CH_LAST},
 };
 
+
 /*
- * returns true if an engine is valid, and it is of the specified type, and buildable by the current player, false otherwise
+ * returns true if an engine is valid, of the specified type, and buildable by
+ * the current player, false otherwise
  *
  * engine = index of the engine to check
  * type   = the type the engine should be of (VEH_xxx)
  */
-bool IsEngineBuildable(int engine, byte type) {
-	Engine *e;
+bool IsEngineBuildable(uint engine, byte type)
+{
+	const Engine *e;
 
 	// check if it's an engine that is in the engine array
-	if (0 > engine || engine >= TOTAL_NUM_ENGINES ) return false;
+	if (engine >= TOTAL_NUM_ENGINES) return false;
 
 	e = DEREF_ENGINE(engine);
 
@@ -928,7 +931,3 @@
 
 	return true;
 }
-
-
-
-

--- a/engine.h	Thu Jan 27 21:00:05 2005 +0000
+++ b/engine.h	Thu Jan 27 21:18:03 2005 +0000
@@ -133,7 +133,7 @@
 void LoadCustomEngineNames(void);
 void DeleteCustomEngineNames(void);
 
-bool IsEngineBuildable(int engine, byte type);
+bool IsEngineBuildable(uint engine, byte type);
 
 enum {
 	NUM_NORMAL_RAIL_ENGINES = 54,

--- a/roadveh_cmd.c	Thu Jan 27 21:00:05 2005 +0000
+++ b/roadveh_cmd.c	Thu Jan 27 21:18:03 2005 +0000
@@ -115,7 +115,7 @@
 	uint tile = TILE_FROM_XY(x,y);
 	Engine *e;
 
-	if (!(IsEngineBuildable(p1, VEH_Road))) return CMD_ERROR;
+	if (!IsEngineBuildable(p1, VEH_Road)) return CMD_ERROR;
 
 	SET_EXPENSES_TYPE(EXPENSES_NEW_VEHICLES);
 

--- a/ship_cmd.c	Thu Jan 27 21:00:05 2005 +0000
+++ b/ship_cmd.c	Thu Jan 27 21:18:03 2005 +0000
@@ -816,7 +816,7 @@
 	uint tile = TILE_FROM_XY(x,y);
 	Engine *e;
 
-	if (!(IsEngineBuildable(p1, VEH_Ship))) return CMD_ERROR;
+	if (!IsEngineBuildable(p1, VEH_Ship)) return CMD_ERROR;
 
 	SET_EXPENSES_TYPE(EXPENSES_NEW_VEHICLES);
 

--- a/train_cmd.c	Thu Jan 27 21:00:05 2005 +0000
+++ b/train_cmd.c	Thu Jan 27 21:18:03 2005 +0000
@@ -525,7 +525,7 @@
 	Engine *e;
 	uint tile;
 
-	if (!(IsEngineBuildable(p1, VEH_Train))) return CMD_ERROR;
+	if (!IsEngineBuildable(p1, VEH_Train)) return CMD_ERROR;
 
 	_cmd_build_rail_veh_var1 = 0;