(svn r11011) -Fix [FS#1129]: GetFirstVehicleInChain did change the game state while being marked const.

-Codechange: do not brute force determine the first vehicle in the chain or previous vehicle, but do it by properly accounting the previous and first pointers when updating the next pointer. This gives a performance increase of about 15% when there are a lot of vehicles in the game.

1 files changed, 20 insertions, 28 deletions

diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
index 97c29a630..caf665cf0 100644
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -161,8 +161,8 @@ void TrainConsistChanged(Vehicle* v)
 	for (Vehicle *u = v; u != NULL; u = u->Next()) {
 		const RailVehicleInfo *rvi_u = RailVehInfo(u->engine_type);
 
-		/* Update the v->first cache. This is faster than having to brute force it later. */
-		if (u->first == NULL) u->first = v;
+		/* Check the v->first cache. */
+		assert(u->First() == v);
 
 		/* update the 'first engine' */
 		u->u.rail.first_engine = v == u ? INVALID_ENGINE : first_engine;
@@ -583,8 +583,8 @@ static CommandCost CmdBuildRailWagon(EngineID engine, TileIndex tile, uint32 fla
 			_new_vehicle_id = v->index;
 
 			VehiclePositionChanged(v);
-			TrainConsistChanged(GetFirstVehicleInChain(v));
-			UpdateTrainGroupID(GetFirstVehicleInChain(v));
+			TrainConsistChanged(v->First());
+			UpdateTrainGroupID(v->First());
 
 			InvalidateWindow(WC_VEHICLE_DEPOT, v->tile);
 			if (IsLocalPlayer()) {
@@ -620,6 +620,7 @@ static CommandCost EstimateTrainCost(EngineID engine, const RailVehicleInfo* rvi
 
 static void AddRearEngineToMultiheadedTrain(Vehicle* v, Vehicle* u, bool building)
 {
+	u = new (u) Train();
 	u->direction = v->direction;
 	u->owner = v->owner;
 	u->tile = v->tile;
@@ -628,7 +629,6 @@ static void AddRearEngineToMultiheadedTrain(Vehicle* v, Vehicle* u, bool buildin
 	u->z_pos = v->z_pos;
 	u->u.rail.track = TRACK_BIT_DEPOT;
 	u->vehstatus = v->vehstatus & ~VS_STOPPED;
-	u = new (u) Train();
 	u->subtype = 0;
 	SetMultiheaded(u);
 	u->spritenum = v->spritenum + 1;
@@ -841,7 +841,6 @@ static Vehicle *UnlinkWagon(Vehicle *v, Vehicle *first)
 	Vehicle *u;
 	for (u = first; GetNextVehicle(u) != v; u = GetNextVehicle(u)) {}
 	GetLastEnginePart(u)->SetNext(GetNextVehicle(v));
-	v->first = NULL; // we shouldn't point to the old first, since the vehicle isn't in that chain anymore
 	return first;
 }
 
@@ -872,11 +871,12 @@ static Vehicle *FindGoodVehiclePos(const Vehicle *src)
  */
 static void AddWagonToConsist(Vehicle *v, Vehicle *dest)
 {
-	UnlinkWagon(v, GetFirstVehicleInChain(v));
+	UnlinkWagon(v, v->First());
 	if (dest == NULL) return;
 
-	v->SetNext(dest->Next());
+	Vehicle *next = dest->Next();
 	dest->SetNext(v);
+	v->SetNext(next);
 	ClearFreeWagon(v);
 	ClearFrontEngine(v);
 }
@@ -933,19 +933,19 @@ CommandCost CmdMoveRailVehicle(TileIndex tile, uint32 flags, uint32 p1, uint32 p
 	}
 
 	/* if an articulated part is being handled, deal with its parent vehicle */
-	while (IsArticulatedPart(src)) src = GetPrevVehicleInChain(src);
+	while (IsArticulatedPart(src)) src = src->Previous();
 	if (dst != NULL) {
-		while (IsArticulatedPart(dst)) dst = GetPrevVehicleInChain(dst);
+		while (IsArticulatedPart(dst)) dst = dst->Previous();
 	}
 
 	/* don't move the same vehicle.. */
 	if (src == dst) return CommandCost();
 
 	/* locate the head of the two chains */
-	Vehicle *src_head = GetFirstVehicleInChain(src);
+	Vehicle *src_head = src->First();
 	Vehicle *dst_head;
 	if (dst != NULL) {
-		dst_head = GetFirstVehicleInChain(dst);
+		dst_head = dst->First();
 		if (dst_head->tile != src_head->tile) return CMD_ERROR;
 		/* Now deal with articulated part of destination wagon */
 		dst = GetLastEnginePart(dst);
@@ -1022,10 +1022,6 @@ CommandCost CmdMoveRailVehicle(TileIndex tile, uint32 flags, uint32 p1, uint32 p
 
 	/* do it? */
 	if (flags & DC_EXEC) {
-		/* clear the ->first cache */
-		for (Vehicle *u = src_head; u != NULL; u = u->Next()) u->first = NULL;
-		for (Vehicle *u = dst_head; u != NULL; u = u->Next()) u->first = NULL;
-
 		/* If we move the front Engine and if the second vehicle is not an engine
 		   add the whole vehicle to the DEFAULT_GROUP */
 		if (IsFrontEngine(src) && !IsDefaultGroupID(src->group_id)) {
@@ -1101,13 +1097,12 @@ CommandCost CmdMoveRailVehicle(TileIndex tile, uint32 flags, uint32 p1, uint32 p
 			}
 			dst->SetNext(src);
 		}
+
 		if (src->u.rail.other_multiheaded_part != NULL) {
 			if (src->u.rail.other_multiheaded_part == src_head) {
 				src_head = src_head->Next();
 			}
 			AddWagonToConsist(src->u.rail.other_multiheaded_part, src);
-			/* previous line set the front engine to the old front. We need to clear that */
-			src->u.rail.other_multiheaded_part->first = NULL;
 		}
 
 		/* If there is an engine behind first_engine we moved away, it should become new first_engine
@@ -1218,8 +1213,8 @@ CommandCost CmdSellRailWagon(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 
 	SET_EXPENSES_TYPE(EXPENSES_NEW_VEHICLES);
 
-	while (IsArticulatedPart(v)) v = GetPrevVehicleInChain(v);
-	Vehicle *first = GetFirstVehicleInChain(v);
+	while (IsArticulatedPart(v)) v = v->Previous();
+	Vehicle *first = v->First();
 
 	/* make sure the vehicle is stopped in the depot */
 	if (CheckTrainStoppedInDepot(first) < 0) {
@@ -1262,9 +1257,6 @@ CommandCost CmdSellRailWagon(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 			if ((flags & DC_EXEC) && v == first) {
 				Vehicle *new_f = GetNextVehicle(first);
 
-				/* 2.1 If the first wagon is sold, update the first-> pointers to NULL */
-				for (Vehicle *tmp = first; tmp != NULL; tmp = tmp->Next()) tmp->first = NULL;
-
 				/* 2.2 If there are wagons present after the deleted front engine, check
 				 * if the second wagon (which will be first) is an engine. If it is one,
 				 * promote it as a new train, retaining the unitnumber, orders */
@@ -1633,7 +1625,7 @@ CommandCost CmdReverseTrainDirection(TileIndex tile, uint32 flags, uint32 p1, ui
 			return_cmd_error(STR_ONLY_TURN_SINGLE_UNIT);
 		}
 
-		Vehicle *front = GetFirstVehicleInChain(v);
+		Vehicle *front = v->First();
 		/* make sure the vehicle is stopped in the depot */
 		if (CheckTrainStoppedInDepot(front) < 0) {
 			return_cmd_error(STR_881A_TRAINS_CAN_ONLY_BE_ALTERED);
@@ -1777,7 +1769,7 @@ CommandCost CmdRefitRailVehicle(TileIndex tile, uint32 flags, uint32 p1, uint32
 	_returned_refit_capacity = num;
 
 	/* Update the train's cached variables */
-	if (flags & DC_EXEC) TrainConsistChanged(GetFirstVehicleInChain(GetVehicle(p1)));
+	if (flags & DC_EXEC) TrainConsistChanged(GetVehicle(p1)->First());
 
 	return cost;
 }
@@ -2718,7 +2710,7 @@ static void *FindTrainCollideEnum(Vehicle *v, void *data)
 			myabs(v->x_pos - tcc->v->x_pos) < 6 &&
 			myabs(v->y_pos - tcc->v->y_pos) < 6 ) {
 
-		Vehicle *coll = GetFirstVehicleInChain(v);
+		Vehicle *coll = v->First();
 
 		/* it can't collide with its own wagons */
 		if (tcc->v == coll ||
@@ -2807,7 +2799,7 @@ static void TrainController(Vehicle *v, bool update_image)
 	Vehicle *prev;
 
 	/* For every vehicle after and including the given vehicle */
-	for (prev = GetPrevVehicleInChain(v); v != NULL; prev = v, v = v->Next()) {
+	for (prev = v->Previous(); v != NULL; prev = v, v = v->Next()) {
 		DiagDirection enterdir = DIAGDIR_BEGIN;
 		bool update_signals = false;
 		BeginVehicleMove(v);
@@ -2945,7 +2937,7 @@ static void TrainController(Vehicle *v, bool update_image)
 					v->tile = gp.new_tile;
 
 					if (GetTileRailType(gp.new_tile) != GetTileRailType(gp.old_tile)) {
-						TrainPowerChanged(GetFirstVehicleInChain(v));
+						TrainPowerChanged(v->First());
 					}
 
 					v->u.rail.track = chosen_track;