X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=moebius2.git;a=blobdiff_plain;f=mgraph.c;h=23a10e352ffa69bc91f9a4c9185fd911e90dbfd1;hp=3233890a5100e87beea2cee3919bdec7ed25c994;hb=190a54bc07e4c1497938a31373543650d3f19c55;hpb=96318dec79e12d23d718139bca74f5d33cd52253

diff --git a/mgraph.c b/mgraph.c
index 3233890..23a10e3 100644
--- a/mgraph.c
+++ b/mgraph.c
@@ -1,35 +1,26 @@
-#include "mgraph.h"
+/*
+ * Graph topology
+ */
 
-static const unsigned dx[V6]= {   0,  +1,  -1,  +1,  -1,   0  },
-                      dy[V6]= { +Y1, +Y1,   0,   0, -Y1, -Y1  };
+#include "mgraph.h"
 
+static const unsigned dx[2][V6]= {{  +1,   0,  -1,  -1,  -1,   0  },
+				  {  +1,  +1,   0,  -1,   0,  +1  }},
+                      dy[V6]=     {   0, -Y1, -Y1,   0, +Y1, +Y1  };
 
 int edge_end2(unsigned v1, int e) {
-  /* The topology is equivalent to that of a square lattice with only
-   * half of the diagonals.  Ie, the result of shearing the triangular
-   * lattice to make the lines of constant x vertical.  This gives
-   * these six directions:
-   *
-   *                0  1
-   *                | /
-   *                |/
-   *             2--*--3
-   * 		   /|
-   * 		  / |
-   * 		 4  5
-   *
-   * This also handily makes vertical the numbering discontinuity,
-   * where the join happens.
-   */
   unsigned x, y;
 
   y= (v1 & YMASK) + dy[e];
-  if (y & ~YMASK) return -1;
+  if (y >= Y*Y1) return -1;
 
-  x= (v1 & XMASK) + dx[e];
+  x= (v1 & XMASK) + dx[(v1 >> YSHIFT) & 1][e];
   if (x & ~XMASK) {
+    //int orgy= y;
     y= (Y-1)*Y1 - y;
     x &= XMASK;;
+    //printf("%40s %02x -%d-> %02x  (was %02x) \n", "", v1, e, x|y, x|orgy);
   }
+  
   return x | y;
 }