Problems(?) and fixes

[benjub]

I noticed the following four potential problems (unless they are signs of my misunderstanding). I can make a PR for some/all of them if you agree.

1. ocaml-hashcons/hashcons.ml

   Line 73 in 9d6a785

   t.table <- newt.table;

   
   Shouldn't one also update t.totsize, by t.totsize <- newt.totsize?

2. ocaml-hashcons/hashcons.ml

   Lines 110 to 116 in 9d6a785

   	match Weak.get bucket i with
   	| Some v when v.node = d ->
   	begin match Weak.get bucket i with
   	| Some v -> v
   	| None -> loop (i+1)
   	end
   	| _ -> loop (i+1)

   
   It looks like there is a redundant call to Weak.get (maybe this is due to some limitations in early versions of Weak and its interactions with the GC?). These lines can probably be replaced by:

      match Weak.get bucket i with
      | Some v when v.node = d -> v
      | Some _ | None -> loop (succ i)

(the variant when v.hkey = hkey && v.node = d, which allows fast rejection, is probably unnecessary since the equality v.node = d is efficient: this is precisely the purpose of maximal hashconsing).

3. ocaml-hashcons/hashcons.ml

   Line 64 in 9d6a785

   let next_sz n = min (3*n/2 + 3) (Sys.max_array_length - 1)

   
   

   ocaml-hashcons/hashcons.ml

   Line 82 in 9d6a785

   let newsz = min (3 * sz / 2 + 3) (Sys.max_array_length - 1) in

Both values are capped at Sys.max_array_length - 1, but the first concerns array lengths, so can be capped at Sys.max_array_length, while the second concerns bucket sizes, so should be capped at Obj.Ephemeron.max_ephe_length (which is currently Sys.max_array_length - 2). Also, is the growth rate purposefully, or accidentally the same?

4. Most integer equality checks in the file use == (although some use =, with no clear pattern of when which is used). Why not use = everywhere? Or Int.equal?