--- a/tile.h	Sun Mar 05 11:18:34 2006 +0000
+++ b/tile.h	Sun Mar 05 12:22:20 2006 +0000
@@ -44,6 +44,12 @@
 	INVALID_DIAGDIR = 0xFF,
 } DiagDirection;
 
+static inline DiagDirection ReverseDiagDir(DiagDirection d)
+{
+	return 2 ^ d;
+}
+
+
 /* the 2 axis */
 typedef enum Axis {
 	AXIS_X = 0,