(svn r9425) -Codechange/Fix (FS#689): Housekeeping in the convert rail functions: Changed the order of error checks to generate more meaningful error messages, added some doxygen comments and replaced bitshifting by proper mathematical operations

src/rail_cmd.cpp

@@ -849,15 +849,24 @@ int32 CmdRemoveSignalTrack(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 
 typedef int32 DoConvertRailProc(TileIndex tile, RailType totype, bool exec);
 
+/**
+ * Switches the rail type.
+ * Railtypes are stored on a per-tile basis, not on a per-track basis, so
+ * all the tracks in the given tile will be converted.
+ * @param tile        The tile on which the railtype is to be convert.
+ * @param totype      The railtype we want to convert to
+ * @param exec        Switches between test and execute mode
+ * @return            The cost and state of the operation
+ * @retval CMD_ERROR  An error occured during the operation.
+ */
 static int32 DoConvertRail(TileIndex tile, RailType totype, bool exec)
 {
 	if (!CheckTileOwnership(tile)) return CMD_ERROR;
 
-	if (!EnsureNoVehicle(tile) && (!IsCompatibleRail(GetRailType(tile), totype) || IsPlainRailTile(tile))) return CMD_ERROR;
-
-	// tile is already of requested type?
 	if (GetRailType(tile) == totype) return CMD_ERROR;
 
+	if (!EnsureNoVehicle(tile) && (!IsCompatibleRail(GetRailType(tile), totype) || IsPlainRailTile(tile))) return CMD_ERROR;
+
 	// 'hidden' elrails can't be downgraded to normal rail when elrails are disabled
 	if (_patches.disable_elrails && totype == RAILTYPE_RAIL && GetRailType(tile) == RAILTYPE_ELECTRIC) return CMD_ERROR;
 

src/road_cmd.cpp

@@ -367,6 +367,14 @@ do_clear:;
 	return cost;
 }
 
+/**
+ * Switches the rail type on a level crossing.
+ * @param tile        The tile on which the railtype is to be convert.
+ * @param totype      The railtype we want to convert to
+ * @param exec        Switches between test and execute mode
+ * @return            The cost and state of the operation
+ * @retval CMD_ERROR  An error occured during the operation.
+ */
 int32 DoConvertStreetRail(TileIndex tile, RailType totype, bool exec)
 {
 	// not a railroad crossing?
@@ -386,7 +394,7 @@ int32 DoConvertStreetRail(TileIndex tile, RailType totype, bool exec)
 		YapfNotifyTrackLayoutChange(tile, FindFirstTrack(GetCrossingRailBits(tile)));
 	}
 
-	return _price.build_rail >> 1;
+	return _price.build_rail / 2;
 }
 
 

src/station_cmd.cpp

@@ -1120,6 +1120,14 @@ static int32 RemoveRailroadStation(Station *st, TileIndex tile, uint32 flags)
 	return cost;
 }
 
+/**
+ * Switches the rail type at a railway station tile.
+ * @param tile        The tile on which the railtype is to be convert.
+ * @param totype      The railtype we want to convert to
+ * @param exec        Switches between test and execute mode
+ * @return            The cost and state of the operation
+ * @retval CMD_ERROR  An error occured during the operation.
+ */
 int32 DoConvertStationRail(TileIndex tile, RailType totype, bool exec)
 {
 	const Station* st = GetStationByTile(tile);
@@ -1140,7 +1148,7 @@ int32 DoConvertStationRail(TileIndex tile, RailType totype, bool exec)
 		YapfNotifyTrackLayoutChange(tile, GetRailStationTrack(tile));
 	}
 
-	return _price.build_rail >> 1;
+	return _price.build_rail / 2;
 }
 
 /**

src/tunnelbridge_cmd.cpp

@@ -696,6 +696,16 @@ static int32 ClearTile_TunnelBridge(TileIndex tile, byte flags)
 	return CMD_ERROR;
 }
 
+/**
+ * Switches the rail type for a tunnel or a bridgehead. As the railtype
+ * on the bridge are determined by the one of the bridgehead, this
+ * functions converts the railtype on the entire bridge.
+ * @param tile        The tile on which the railtype is to be convert.
+ * @param totype      The railtype we want to convert to
+ * @param exec        Switches between test and execute mode
+ * @return            The cost and state of the operation
+ * @retval CMD_ERROR  An error occured during the operation.
+ */
 int32 DoConvertTunnelBridgeRail(TileIndex tile, RailType totype, bool exec)
 {
 	TileIndex endtile;
@@ -724,7 +734,7 @@ int32 DoConvertTunnelBridgeRail(TileIndex tile, RailType totype, bool exec)
 			YapfNotifyTrackLayoutChange(tile, track);
 			YapfNotifyTrackLayoutChange(endtile, track);
 		}
-		return (length + 1) * (_price.build_rail >> 1);
+		return (length + 1) * (_price.build_rail / 2);
 	} else if (IsBridge(tile) && GetBridgeTransportType(tile) == TRANSPORT_RAIL) {
 
 		if (!CheckTileOwnership(tile)) return CMD_ERROR;
@@ -758,7 +768,7 @@ int32 DoConvertTunnelBridgeRail(TileIndex tile, RailType totype, bool exec)
 			}
 		}
 
-		return (DistanceManhattan(tile, endtile) + 1) * (_price.build_rail >> 1);
+		return (DistanceManhattan(tile, endtile) + 1) * (_price.build_rail / 2);
 	} else {
 		return CMD_ERROR;
 	}