Changed the fix from the last commit by solving the problem in a

different way.  Added a routine to remove all layers of a contact
from all planes except the contact's base plane before finding
and processing contacts.  This causes ExtFindRegions() to find
and process only one tile on one plane per contact, so there are
no redundant contact entries.  Also, any overlapping stacked
contacts are resolved, which avoids the very common error of
contacts not being processed at the correct size because they
are being processed per tile for chopped-up areas.

resis/ResMain.c

@@ -867,6 +867,61 @@ resExpandDevFunc(tile, cx)
     return 1;
 }
 
+/*
+ *-------------------------------------------------------------------------
+ *
+ * ResShaveContacts ---
+ *
+ *	Remove the top layer off of every contact in the design, leaving
+ *	only the bottom layer.  This also resolves issues with stacked
+ *	contacts by leaving clean contact areas where stacked types
+ *	overlap.  Contacts are removed from the plane above the search
+ *	plane, so the removal does not corrupt the current plane search.
+ *
+ * Results:
+ *	Return 0 to keep the search going.
+ *
+ *-------------------------------------------------------------------------
+ */
+
+int
+ResShaveContacts(tile, def)
+    Tile *tile;
+    CellDef *def;
+{
+    TileType ttype;
+    TileTypeBitMask *rmask;
+    Rect area;
+    Plane *plane;
+    int pNum;
+    int pMask;
+
+    /* To do:  Handle split tiles, although this is unlikely for
+     * contact types.
+     */
+    ttype = TiGetType(tile);
+
+    if (DBIsContact(ttype))
+    {
+	/* Remove the contact type from the plane above */
+	TiToRect(tile, &area);
+	pMask = DBTypePlaneMaskTbl[ttype];
+	for (pNum = PL_TECHDEPBASE; pNum < DBNumPlanes; pNum++)
+	    if (PlaneMaskHasPlane(pMask, pNum))
+		break;
+
+	for (++pNum; pNum < DBNumPlanes; pNum++)
+	    if (PlaneMaskHasPlane(pMask, pNum))
+	    {
+		plane = def->cd_planes[pNum];
+		DBPaintPlane(plane, &area, DBStdEraseTbl(ttype, pNum),
+			(PaintUndoInfo *)NULL);
+	    }
+    }
+
+    return 0;
+}
+
 /*
  *-------------------------------------------------------------------------
  *
@@ -1028,6 +1083,21 @@ ResExtractNet(node, goodies, cellname)
 
     ExtResetTiles(scx.scx_use->cu_def, extUnInit);
 
+    /* To avoid issues with overlapping stacked contact types and	*/
+    /* double-counting contacts on multiple planes, erase the top	*/
+    /* contact layers of all contacts.  ExtFindRegions() will still	*/
+    /* find the connectivity above but will only process one tile per	*/
+    /* contact.	  This temporarily creates an improper database, but	*/
+    /* the contacts are all immediately erased by ResDissolveContacts().*/
+
+    for (pNum = PL_TECHDEPBASE; pNum < DBNumPlanes; pNum++)
+    {
+	Plane *plane = ResUse->cu_def->cd_planes[pNum];
+	DBSrPaintArea(plane->pl_hint, plane, &(ResUse->cu_def->cd_bbox),
+		&DBAllButSpaceAndDRCBits, ResShaveContacts,
+		(ClientData)ResUse->cu_def);
+    }
+
     /* Find all contacts in design and note their position */
 
     /* NOTE:  ExtFindRegions() will call ResFirst or ResEach for BOTH	*/

resis/ResMakeRes.c

@@ -895,14 +895,7 @@ ResDoContacts(contact, nodes, resList)
 		resistor->rr_cl = squaresy;
 		resistor->rr_width = squaresx;
 
-		/* NOTE: ExtFindRegions() finds tiles on the top AND	*/
-		/* bottom planes of the contact.  So there are two	*/
-		/* tile entries per contact, in parallel.  To prevent	*/
-		/* double-counting, double the resistance of each	*/
-		/* entry;  this is (probably?) easier than limiting the	*/
-		/* entries to a single plane per contact.		*/
-
-		resistor->rr_value = 2.0 *
+		resistor->rr_value =
 		    	(float)ExtCurStyle->exts_viaResist[contact->cp_type] /
 			(float)(squaresx * squaresy);
 #ifdef ARIEL