GENmodel, GENinstance, change layout, #4/4, complete the change

currently each and every device specific instance and model structure
  duplicates the memory layout of a struct GENmodel / GENinstance

further the first structure elements behind a GENinstance header
  are reinterpreted as a sort of a generic "node" array.

This business is very error prone, and makes it difficult to
  extend struct GENmodel / struct GENinstance.

This patch makes this business much more bearable.

src/include/ngspice/gendefs.h

@@ -21,10 +21,19 @@ struct GENinstance {
                                      * current model*/
     IFuid GENname;  /* pointer to character string naming this instance */
     int GENstate;   /* state index number */
-    int GENnode[7]; /* node numbers to which this instance is connected to */
-                    /* carefull, thats overlayed into the actual device structs */
+
+    /* The actual device instance structs have to place their node elements
+     *   right after the the end of struct GENinstance
+     *   where they will be accessed by generic GENnode()[]
+     * A notable exception is the XSPICE MIF device
+     */
 };
 
+static inline int *
+GENnode(struct GENinstance *inst) {
+    return (int*)(inst + 1);
+}
+
 
 /* per model data */
 

src/include/ngspice/mifdefs.h

@@ -44,6 +44,7 @@ NON-STANDARD FEATURES
 
 
 #include  "ngspice/mifcmdat.h"
+#include  "ngspice/gendefs.h"
 #include "ngspice/ifsim.h"
 
 

src/include/ngspice/numgen.h

@@ -22,11 +22,6 @@ typedef struct sGENnumModel {	/* model structure for a numerical device */
 
     struct GENmodel gen;
 
-#define GENmodType gen.GENmodType
-#define GENnextModel(inst) ((struct sGENnumModel *)((inst)->gen.GENnextModel))
-#define GENinstances(inst) ((GENinstance *)((inst)->gen.GENinstances))
-#define GENmodName gen.GENmodName
-
     MESHcard *GENxMeshes;	/* list of xmesh cards */
     MESHcard *GENyMeshes;	/* list of ymesh cards */
     DOMNcard *GENdomains;	/* list of domain cards */