One more change to the extraction method to avoid extracting the

substrate more than once for the same subcell, since the substrate
extraction method scans the entire plane area;  this was making
large standard cell layouts extract very slowly, as every component
cell was causing the substrate search to be repeated.

database/database.h.in

@@ -498,6 +498,11 @@ typedef struct celluse
  */  
 #define CU_SELECT_NET	0x02
 #define CU_SELECT_CHUNK	0x04
+/* CU_SUB_EXTRACTED is a temporary flag indicating that the substrate
+ *		    of the use has been extracted and the extraction
+ *		    does not need to be repeated for this use.
+ */
+#define CU_SUB_EXTRACTED 0x08
 
 /* Character prefix used to denote a locked cell use in a .mag file */
 #define CULOCKCHAR	'*'