Index: src/town_cmd.cpp
===================================================================
--- src/town_cmd.cpp	(Revision 10980)
+++ src/town_cmd.cpp	(Arbeitskopie)
@@ -563,20 +563,23 @@
 	/* not used */
 }
 
+static TileIndex TileByDiagDirAndDist(TileIndex tile, int diag_dir, int dist) {
+	return (tile + dist * TileOffsByDiagDir((DiagDirection)diag_dir));
+}
 
-static const TileIndexDiffC _roadblock_tileadd[] = {
-	{ 0, -1},
-	{ 1,  0},
-	{ 0,  1},
-	{-1,  0},
+static TileIndex TileByDiagDir(TileIndex tile, int diag_dir) {
+	return TileByDiagDirAndDist(tile, diag_dir, 1);
+}
 
-	/* Store the first 3 elements again.
-	 * Lets us rotate without using &3. */
-	{ 0, -1},
-	{ 1,  0},
-	{ 0,  1}
-};
+static TileIndex TileByMirroredDiagDirAndDist(TileIndex tile, int mirrored_diag_dir, int dist) {
+	mirrored_diag_dir = 3 - (mirrored_diag_dir % 4);
+	return TileByDiagDirAndDist(tile, mirrored_diag_dir, dist);
+}
 
+static TileIndex TileByMirroredDiagDir(TileIndex tile, int mirrored_diag_dir) {
+	return TileByMirroredDiagDirAndDist(tile, mirrored_diag_dir, 1);
+}
+
 /**
  * Distance multiplyer
  * Defines the possible distances between 2 road tiles
@@ -647,12 +650,13 @@
  * @return true if one of the neighboring tiles at the
  *  given distance is a road tile else
  */
-static bool NeighborIsRoadTile(TileIndex tile, int dir, RoadBlockTitleDistance dist_multi)
+static bool IsNeighborRoadTile(TileIndex tile, int dir, RoadBlockTitleDistance dist_multi)
 {
-	return (HASBIT(GetTownRoadMask(TILE_ADD(tile, dist_multi * ToTileIndexDiff(_roadblock_tileadd[dir + 1]))), dir ^ 2) ||
-			HASBIT(GetTownRoadMask(TILE_ADD(tile, dist_multi * ToTileIndexDiff(_roadblock_tileadd[dir + 3]))), dir ^ 2) ||
-			HASBIT(GetTownRoadMask(TILE_ADD(tile, dist_multi * (ToTileIndexDiff(_roadblock_tileadd[dir + 1]) + ToTileIndexDiff(_roadblock_tileadd[dir + 2])))), dir) ||
-			HASBIT(GetTownRoadMask(TILE_ADD(tile, dist_multi * (ToTileIndexDiff(_roadblock_tileadd[dir + 3]) + ToTileIndexDiff(_roadblock_tileadd[dir + 2])))), dir));
+	const TileIndex dummy = TileByMirroredDiagDirAndDist(tile, dir + 2, dist_multi);
+	return (HASBIT(GetTownRoadMask(TileByMirroredDiagDirAndDist(tile, dir + 1, dist_multi)), dir ^ 2) ||
+			HASBIT(GetTownRoadMask(TileByMirroredDiagDirAndDist(tile, dir + 3, dist_multi)), dir ^ 2) ||
+			HASBIT(GetTownRoadMask(TileByMirroredDiagDirAndDist(dummy, dir + 1, dist_multi)), dir) ||
+			HASBIT(GetTownRoadMask(TileByMirroredDiagDirAndDist(dummy, dir + 3, dist_multi)), dir));
 }
 
 static bool IsRoadAllowedHere(TileIndex tile, int dir)
@@ -685,11 +689,11 @@
 				default: NOT_REACHED();
 
 				case TL_ORIGINAL: /* Disallow the road if any neighboring tile has a road (distance: 1) */
-					return !NeighborIsRoadTile(tile, dir, RB_TILE_DIST1);
+					return !IsNeighborRoadTile(tile, dir, RB_TILE_DIST1);
 
 				case TL_BETTER_ROADS: /* Disallow the road if any neighboring tile has a road (distance: 1 and 2). */
-					return !(NeighborIsRoadTile(tile, dir, RB_TILE_DIST1) ||
-							NeighborIsRoadTile(tile, dir, RB_TILE_DIST2));
+					return !(IsNeighborRoadTile(tile, dir, RB_TILE_DIST1) ||
+							IsNeighborRoadTile(tile, dir, RB_TILE_DIST2));
 			}
 		}
 
@@ -840,7 +844,7 @@
 
 	/* Check the tiles E,N,W and S of the current tile. */
 	for (uint i = 0; i < 4; i++) {
-		if (IsTileType(TILE_ADD(tile, ToTileIndexDiff(_roadblock_tileadd[i])), MP_HOUSE)) {
+		if (IsTileType(TileByMirroredDiagDir(tile, i), MP_HOUSE)) {
 			counter++;
 		}
 
@@ -921,7 +925,7 @@
 					} while (a == b);
 				}
 
-				if (!IsRoadAllowedHere(TILE_ADD(tile, ToTileIndexDiff(_roadblock_tileadd[a])), a)) {
+				if (!IsRoadAllowedHere(TileByMirroredDiagDir(tile, a), a)) {
 					/* A road is not allowed to continue the randomized road,
 					 *   return if the road we're trying to build is curved. */
 					if (a != (b ^ 2)) {
@@ -929,8 +933,8 @@
 					}
 
 					/* Return if neither side of the new road is a house */
-					if (!IsTileType(TILE_ADD(tile, ToTileIndexDiff(_roadblock_tileadd[a + 1])), MP_HOUSE) &&
-							!IsTileType(TILE_ADD(tile, ToTileIndexDiff(_roadblock_tileadd[a + 3])), MP_HOUSE)) {
+					if (!IsTileType(TileByMirroredDiagDir(tile, a + 1), MP_HOUSE) &&
+							!IsTileType(TileByMirroredDiagDir(tile, a + 3), MP_HOUSE)) {
 						return;
 					}
 
@@ -984,7 +988,7 @@
 		if (HASBIT(mask, i)) return;
 
 		/* This is the tile we will reach if we extend to this direction. */
-		tmptile = TILE_ADD(tile, ToTileIndexDiff(_roadblock_tileadd[i]));
+		tmptile = TileByMirroredDiagDir(tile, i);
 
 		/* Don't do it if it reaches to water. */
 		if (IsClearWaterTile(tmptile)) return;
@@ -998,7 +1002,7 @@
 
 			case TL_3X3_GRID: /* Use 2x2 grid afterwards! */
 				/* Fill gap if house has enougth neighbors */
-				tmptile2 = TILE_ADD(tmptile, ToTileIndexDiff(_roadblock_tileadd[i]));
+				tmptile2 = TileByMirroredDiagDir(tmptile, i);
 				if (NeighborsAreHouseTiles(tmptile2) && BuildTownHouse(t1, tmptile2)) {
 					_grow_town_result = -1;
 				}
@@ -1010,7 +1014,7 @@
 
 			case TL_BETTER_ROADS: /* Use original afterwards! */
 				/* Fill gap if house has enougth neighbors */
-				tmptile2 = TILE_ADD(tmptile, ToTileIndexDiff(_roadblock_tileadd[i]));
+				tmptile2 = TileByMirroredDiagDir(tmptile, i);
 				if (NeighborsAreHouseTiles(tmptile2) && BuildTownHouse(t1, tmptile2)) {
 					_grow_town_result = -1;
 				}
@@ -1143,7 +1147,7 @@
 		/* Select a random bit from the blockmask, walk a step
 		 * and continue the search from there. */
 		do block = Random() & 3; while (!HASBIT(mask, block));
-		tile += ToTileIndexDiff(_roadblock_tileadd[block]);
+		tile = TileByMirroredDiagDir(tile, block);
 
 		if (IsTileType(tile, MP_ROAD)) {
 			/* Don't allow building over roads of other cities */