Index: trunk/src/layer.c
===================================================================
--- trunk/src/layer.c	(revision 14724)
+++ trunk/src/layer.c	(revision 14725)
@@ -724,6 +724,25 @@
 	return lay;
 }
 
+unsigned long pcb_layer_hash_bound(pcb_layer_t *ly)
+{
+	unsigned long hash;
+
+	assert(ly->is_bound);
+
+	hash  = (unsigned long)arclist_length(&ly->Arc);
+	hash ^= (unsigned long)linelist_length(&ly->Line);
+	hash ^= (unsigned long)textlist_length(&ly->Text);
+	hash ^= (unsigned long)polylist_length(&ly->Polygon);
+	hash ^= (unsigned long)ly->comb ^ (unsigned long)ly->meta.bound.type;
+
+	if (ly->meta.bound.type & PCB_LYT_INTERN)
+		hash ^= ly->meta.bound.stack_offs;
+
+	return hash;
+}
+
+
 int pcb_layer_type_map(pcb_layer_type_t type, void *ctx, void (*cb)(void *ctx, pcb_layer_type_t bit, const char *name, int class, const char *class_name))
 {
 	const pcb_layer_type_name_t *n;
Index: trunk/src/layer.h
===================================================================
--- trunk/src/layer.h	(revision 14724)
+++ trunk/src/layer.h	(revision 14725)
@@ -263,6 +263,10 @@
 /* Allocate a new bound layer within data, set it up, but do not do the binding */
 pcb_layer_t *pcb_layer_new_bound(pcb_data_t *data, pcb_layer_type_t type, const char *name);
 
+/* Calculate a hash of a bound layer (ingoring its name) */
+unsigned long pcb_layer_hash_bound(pcb_layer_t *ly);
+
+
 /* Modify tree pointers in dst to point to src's; allocates trees for src if they are not yet allocated */
 void pcb_layer_link_trees(pcb_layer_t *dst, pcb_layer_t *src);
 
Index: trunk/src/obj_subc_hash.c
===================================================================
--- trunk/src/obj_subc_hash.c	(revision 14724)
+++ trunk/src/obj_subc_hash.c	(revision 14725)
@@ -42,13 +42,15 @@
 
 unsigned int pcb_subc_hash(const pcb_subc_t *sc)
 {
-	unsigned int hash = 0;
+	unsigned int hash;
 	int lid;
 	pcb_host_trans_t tr;
 
 	pcb_subc_get_host_trans(sc, &tr);
 
-	for(lid = 0; lid < sc->data->LayerN; lid++) {
+	/* hash layers and layer objects */
+	hash = sc->data->LayerN;
+	for(lid = 0; lid 3< sc->data->LayerN; lid++) {
 		pcb_layer_t *ly = &sc->data->Layer[lid];
 		gdl_iterator_t it;
 		pcb_line_t *l;
@@ -56,7 +58,7 @@
 		pcb_text_t *t;
 		pcb_poly_t *p;
 
-#warning TODO: hash layers
+		hash ^= pcb_layer_hash_bound(ly);
 
 		linelist_foreach(&ly->Arc, &it, a)
 			hash ^= pcb_arc_hash(&tr, a);
@@ -71,6 +73,8 @@
 			hash ^= pcb_poly_hash(&tr, p);
 	}
 
+	/* hash global objects */
+
 	return hash;
 }