X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=moebius2.git;a=blobdiff_plain;f=mgraph.h;h=85f1a3c8d0ef621e8417a2715c1af014df187e91;hp=a5eb61127f6e6cc3fbbf0493d5b53c0fe565d3a1;hb=f5c44e57feae26a81c416d9d7cc69f0accbac8b6;hpb=75293637fe7efbce3f2e873cc792da3bff577fef

diff --git a/mgraph.h b/mgraph.h
index a5eb611..85f1a3c 100644
--- a/mgraph.h
+++ b/mgraph.h
@@ -87,6 +87,7 @@
 #define Y1 (1 << YSHIFT)
 
 #define V6 6
+#define V3 3
 
 #define FOR_VERTEX(v) \
   for ((v)=0; (v)<N; (v)++)
@@ -101,6 +102,8 @@ int edge_end2(unsigned v1, int e);
  * returns  eprime   s.t.  v1==EDGE_END2(v2,eprime) */
 int edge_reverse(int v1, int e);
 
+#define EDGE_OPPOSITE(e) (((e)+V3) % V6)
+
 #define RIM_VERTEX_P(v) (((v) & ~XMASK) == 0 || ((v) & ~XMASK) == (Y-1)*Y1)
 
 #define FOR_VEDGE_X(v1,e,v2,init,otherwise)	\