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(**************************************************************************)
(*                                                                        *)
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(*  Copyright (C) Francois Bobot, Jean-Christophe Filliatre,              *)
(*  Johannes Kanig and Andrei Paskevich.                                  *)
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(*                                                                        *)
(*  This software is free software; you can redistribute it and/or        *)
(*  modify it under the terms of the GNU Library General Public           *)
(*  License version 2.1, with the special exception on linking            *)
(*  described in file LICENSE.                                            *)
(*                                                                        *)
(*  This software is distributed in the hope that it will be useful,      *)
(*  but WITHOUT ANY WARRANTY; without even the implied warranty of        *)
(*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.                  *)
(*                                                                        *)
(**************************************************************************)

(*s Hash tables for hash-consing. (Some code is borrowed from the ocaml
    standard library, which is copyright 1996 INRIA.) *)

let gentag =
  let r = ref 0 in
  fun () -> incr r; !r

module type HashedType =
  sig
    type t
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    val equal : t -> t -> bool
    val hash : t -> int
    val tag : int -> t -> t
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  end

module type S =
  sig
    type t
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    val hashcons : t -> t
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    val iter : (t -> unit) -> unit
    val stats : unit -> int * int * int * int * int * int
  end

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module Make(H : HashedType) : (S with type t = H.t) = 
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struct

  type t = H.t

  type table = {
    mutable table : t Weak.t array;
    mutable totsize : int;             (* sum of the bucket sizes *)
    mutable limit : int;               (* max ratio totsize/table length *)
  }

  let emptybucket = Weak.create 0

  let create sz =
    let sz = if sz < 7 then 7 else sz in
    let sz = if sz > Sys.max_array_length then Sys.max_array_length else sz in
    {
      table = Array.create sz emptybucket;
      totsize = 0;
      limit = 3;
    }

  let clear t =
    for i = 0 to Array.length t.table - 1 do
      t.table.(i) <- emptybucket
    done;
    t.totsize <- 0;
    t.limit <- 3
  
  let fold f t init =
    let rec fold_bucket i b accu =
      if i >= Weak.length b then accu else
      match Weak.get b i with
      | Some v -> fold_bucket (i+1) b (f v accu)
      | None -> fold_bucket (i+1) b accu
    in
    Array.fold_right (fold_bucket 0) t.table init

  let count t =
    let rec count_bucket i b accu =
      if i >= Weak.length b then accu else
      count_bucket (i+1) b (accu + (if Weak.check b i then 1 else 0))
    in
    Array.fold_right (count_bucket 0) t.table 0

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

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  let hash n = (H.hash n) land 0x3fffffff

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  let rec resize t =
    let oldlen = Array.length t.table in
    let newlen = next_sz oldlen in
    if newlen > oldlen then begin
      let newt = create newlen in
      newt.limit <- t.limit + 100;          (* prevent resizing of newt *)
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      fold (fun d () -> add newt d (hash d)) t ();
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      t.table <- newt.table;
      t.limit <- t.limit + 2;
    end

  and add t d hkey =
    let index = hkey mod (Array.length t.table) in
    let bucket = t.table.(index) in
    let sz = Weak.length bucket in
    let rec loop i =
      if i >= sz then begin
        let newsz = min (sz + 3) (Sys.max_array_length - 1) in
        if newsz <= sz then 
	  failwith "Hashcons.Make: hash bucket cannot grow more";
        let newbucket = Weak.create newsz in
        Weak.blit bucket 0 newbucket 0 sz;
        Weak.set newbucket i (Some d);
        t.table.(index) <- newbucket;
        t.totsize <- t.totsize + (newsz - sz);
        if t.totsize > t.limit * Array.length t.table then resize t;
      end else begin
        if Weak.check bucket i
        then loop (i+1)
        else Weak.set bucket i (Some d)
      end
    in
    loop 0

  let t = create 5003

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  let hashcons d =
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    let hkey = hash d in
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    let index = hkey mod (Array.length t.table) in
    let bucket = t.table.(index) in
    let sz = Weak.length bucket in
    let rec loop i =
      if i >= sz then begin
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	let hnode = H.tag (gentag ()) d in
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	add t hnode hkey;
	hnode
      end else begin
        match Weak.get_copy bucket i with
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        | Some v when H.equal v d -> 
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	    begin match Weak.get bucket i with
              | Some v -> v
              | None -> loop (i+1)
            end
        | _ -> loop (i+1)
      end
    in
    loop 0
  
  let iter f =
    let rec iter_bucket i b =
      if i >= Weak.length b then () else
      match Weak.get b i with
      | Some v -> f v; iter_bucket (i+1) b
      | None -> iter_bucket (i+1) b
    in
    Array.iter (iter_bucket 0) t.table

  let stats () =
    let len = Array.length t.table in
    let lens = Array.map Weak.length t.table in
    Array.sort compare lens;
    let totlen = Array.fold_left ( + ) 0 lens in
    (len, count t, totlen, lens.(0), lens.(len/2), lens.(len-1))
  
end
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let combine acc n = n * 65599 + acc
let combine2 acc n1 n2 = combine acc (combine n1 n2)
let combine3 acc n1 n2 n3 = combine acc (combine n1 (combine n2 n3))
let combine_list f = List.fold_left (fun acc x -> combine acc (f x))