+ let h_union = Hashtbl.create 511 in
+ let pt_cup s1 s2 =
+ (* special case, since this is a union we want hash(s1,s2) = hash(s2,s1) *)
+ let x = Ptset.hash s1
+ and y = Ptset.hash s2 in
+ let h = if x < y then HASHINT2(x,y) else HASHINT2(y,x) in
+ try
+ Hashtbl.find h_union h
+ with
+ | Not_found -> let s = Ptset.union s1 s2
+ in
+ Hashtbl.add h_union h s;s
+ in
+ let h_add = Hashtbl.create 511 in
+ let pt_add t s =
+ let k = HASHINT2(Tag.hash t,Ptset.hash s) in
+ try
+ Hashtbl.find h_add k
+ with
+ | Not_found -> let r = Ptset.add t s in
+ Hashtbl.add h_add k r;r
+ in