Index: town_cmd.c
===================================================================
--- town_cmd.c	(revision 3328)
+++ town_cmd.c	(working copy)
@@ -49,6 +49,8 @@
  * are then scaled based on that. */
 #define TOWN_GROWTH_FREQUENCY 23
 
+#define BUILDINDSTAGE_COMPLETED 0x03
+
 enum {
 	TOWN_HAS_CHURCH     = 0x02,
 	TOWN_HAS_STADIUM    = 0x04
@@ -87,6 +89,32 @@
 };
 
 
+static byte NewHouseIDFromMap( TileIndex tile )
+{
+	return _m[tile].m4;  /*Standard ID*/
+}
+
+static byte BuildingStage(TileIndex tile)
+{
+	return GB(_m[tile].m3, 6,2);
+}
+
+static void IncBuildingStage( TileIndex tile )
+{
+	AB(_m[tile].m3, 6, 2, 1); /*increase construction stage of one more step*/
+}
+
+static inline Town *GetTownByTile(TileIndex tile)
+{
+	return GetTown(_m[tile].m2 );
+}
+
+static bool HouseLiftIsMoving( TileIndex tile )
+{
+	return HASBIT(_m[tile].m5,7);
+}
+
+
 static void DrawTile_Town(TileInfo *ti)
 {
 	const DrawTownTileStruct *dcts;
@@ -96,8 +124,8 @@
 	/* Retrieve pointer to the draw town tile struct */
 	{
 		/* this "randomizes" on the (up to) 4 variants of a building */
-		byte gfx   = _m[ti->tile].m4;
-		byte stage = GB(_m[ti->tile].m3, 6, 2);
+		byte gfx = NewHouseIDFromMap(ti->tile);//pointer to house type*/
+		byte stage = BuildingStage(ti->tile);
 		uint variant;
 		variant  = ti->x >> 4;
 		variant ^= ti->x >> 6;
@@ -165,7 +193,7 @@
 	// Not exactly sure when this happens, but probably when a house changes.
 	// Before this was just a return...so it'd leak animated tiles..
 	// That bug seems to have been here since day 1??
-	if (!(_housetype_extra_flags[_m[tile].m4] & 0x20)) {
+	if (!(_housetype_extra_flags[NewHouseIDFromMap(tile)] & 0x20)) {
 		DeleteAnimatedTile(tile);
 		return;
 	}
@@ -254,22 +282,26 @@
 {
 	assert(IsTileType(tile, MP_HOUSE));
 
-	if (_m[tile].m5 & 0x80) return;
+	if (HouseLiftIsMoving(tile)) return;  //house with a moving lift is indeed finished
 
 	AB(_m[tile].m5, 0, 3, 1);
 	if (GB(_m[tile].m5, 0, 3) != 0) return;
+	/*m5 bits 2..0:
+	Construction counter, for buildings under construction. Incremented on every
+	periodic tile processing. On wraparound, the stage of construction in m3 is increased*/
 
-	_m[tile].m3 = _m[tile].m3 + 0x40;
+	IncBuildingStage( tile );  /*increase construction stage of one more step*/
 
-	if ((_m[tile].m3 & 0xC0) == 0xC0) {
-		ChangePopulation(GetTown(_m[tile].m2), _housetype_population[_m[tile].m4]);
+	if (BuildingStage(tile) == BUILDINDSTAGE_COMPLETED) {  //House is completed
+		/*Now, construction is completed.  Can add population of building to the town*/
+		ChangePopulation(GetTownByTile(tile), _housetype_population[NewHouseIDFromMap(tile)]);
 	}
 	MarkTileDirtyByTile(tile);
 }
 
 static void MakeTownHouseBigger(TileIndex tile)
 {
-	uint flags = _house_more_flags[_m[tile].m4];
+	uint flags = _house_more_flags[NewHouseIDFromMap(tile)];
 	if (flags & 8) MakeSingleHouseBigger(TILE_ADDXY(tile, 0, 0));
 	if (flags & 4) MakeSingleHouseBigger(TILE_ADDXY(tile, 0, 1));
 	if (flags & 2) MakeSingleHouseBigger(TILE_ADDXY(tile, 1, 0));
@@ -282,20 +314,22 @@
 	Town *t;
 	uint32 r;
 
-	if ((_m[tile].m3 & 0xC0) != 0xC0) {
+
+	if (BuildingStage(tile) != BUILDINDSTAGE_COMPLETED) {
+		/*Construction is not completed. See if we can go further in construction*/
 		MakeTownHouseBigger(tile);
 		return;
 	}
 
-	house = _m[tile].m4;
+	house = NewHouseIDFromMap(tile);
 	if (_housetype_extra_flags[house] & 0x20 &&
-			!(_m[tile].m5 & 0x80) &&
+			!HouseLiftIsMoving( tile ) &&
 			CHANCE16(1, 2) &&
 			AddAnimatedTile(tile)) {
 		_m[tile].m5 = (_m[tile].m5 & 0x40) | 0x80;
 	}
 
-	t = GetTown(_m[tile].m2);
+	t = GetTownByTile(tile);
 
 	r = Random();
 
@@ -348,12 +382,12 @@
 	if (!EnsureNoVehicle(tile)) return CMD_ERROR;
 	if (flags&DC_AUTO && !(flags&DC_AI_BUILDING)) return_cmd_error(STR_2004_BUILDING_MUST_BE_DEMOLISHED);
 
-	house = _m[tile].m4;
+	house = NewHouseIDFromMap(tile);
 	cost = _price.remove_house * _housetype_remove_cost[house] >> 8;
 
 	rating = _housetype_remove_ratingmod[house];
 	_cleared_town_rating += rating;
-	_cleared_town = t = GetTown(_m[tile].m2);
+	_cleared_town = t = GetTownByTile(tile);
 
 	if (_current_player < MAX_PLAYERS) {
 		if (rating > t->ratings[_current_player] && !(flags & DC_NO_TOWN_RATING) && !_cheats.magic_bulldozer.value) {
@@ -372,7 +406,7 @@
 
 static void GetAcceptedCargo_Town(TileIndex tile, AcceptedCargo ac)
 {
-	byte type = _m[tile].m4;
+	byte type = NewHouseIDFromMap(tile);
 
 	ac[CT_PASSENGERS] = _housetype_cargo_passengers[type];
 	ac[CT_MAIL]       = _housetype_cargo_mail[type];
@@ -382,8 +416,8 @@
 
 static void GetTileDesc_Town(TileIndex tile, TileDesc *td)
 {
-	td->str = _town_tile_names[_m[tile].m4];
-	if ((_m[tile].m3 & 0xC0) != 0xC0) {
+	td->str = _town_tile_names[NewHouseIDFromMap(tile)];
+	if ((BuildingStage(tile) != BUILDINDSTAGE_COMPLETED)) {
 		SetDParamX(td->dparam, 0, td->str);
 		td->str = STR_2058_UNDER_CONSTRUCTION;
 	}
@@ -733,7 +767,7 @@
 
 		if (IsTileType(tile, MP_STREET)) {
 			/* Don't allow building over roads of other cities */
-			if (IsTileOwner(tile, OWNER_TOWN) && GetTown(_m[tile].m2) != t)
+			if (IsTileOwner(tile, OWNER_TOWN) && GetTownByTile(tile) != t)
 				_grow_town_result = -1;
 			else if (_game_mode == GM_EDITOR) {
 				/* If we are in the SE, and this road-piece has no town owner yet, it just found an
@@ -1377,7 +1411,7 @@
 
 static void ClearTownHouse(Town *t, TileIndex tile)
 {
-	uint house = _m[tile].m4;
+	uint house = NewHouseIDFromMap(tile);
 	uint eflags;
 
 	assert(IsTileType(tile, MP_HOUSE));
@@ -1399,9 +1433,8 @@
 		}
 	}
 
-	// Remove population from the town if the
-	// house is finished.
-	if ((~_m[tile].m3 & 0xC0) == 0) {
+	// Remove population from the town if the house is finished.
+	if (BuildingStage(tile) == BUILDINDSTAGE_COMPLETED) {
 		ChangePopulation(t, -_housetype_population[house]);
 	}
 
@@ -1484,7 +1517,7 @@
 	for (tile = 0; tile < MapSize(); ++tile) {
 		switch (GetTileType(tile)) {
 			case MP_HOUSE:
-				if (GetTown(_m[tile].m2) == t)
+				if (GetTownByTile(tile) == t)
 					DoCommandByTile(tile, 0, 0, DC_EXEC, CMD_LANDSCAPE_CLEAR);
 				break;
 
@@ -1833,7 +1866,7 @@
 				IsTileType(tile, MP_STREET) &&
 				(IsLevelCrossing(tile) ? _m[tile].m3 : GetTileOwner(tile)) == OWNER_TOWN
 			))
-		return GetTown(_m[tile].m2);
+		return GetTownByTile(tile);
 
 	FOR_ALL_TOWNS(t) {
 		if (t->xy != 0) {