(svn r3777) Add some functions to handle tunnels

tunnel_map.c

@@ -0,0 +1,25 @@
+/* $Id$ */
+
+#include "stdafx.h"
+#include "openttd.h"
+#include "tile.h"
+#include "tunnel_map.h"
+
+TileIndex GetOtherTunnelEnd(TileIndex tile)
+{
+	DiagDirection dir = GetTunnelDirection(tile);
+	TileIndexDiff delta = TileOffsByDir(dir);
+	uint z = GetTileZ(tile);
+
+	dir = ReverseDiagDir(dir);
+	do {
+		tile += delta;
+	} while (
+		!IsTileType(tile, MP_TUNNELBRIDGE) ||
+		GB(_m[tile].m5, 4, 4) != 0 ||
+		GetTunnelDirection(tile) != dir ||
+		GetTileZ(tile) != z
+	);
+
+	return tile;
+}