Source file my_hash_cons.ml

(**************************************************************************)
(*                                                                        *)
(*  Copyright (C) Jean-Christophe Filliatre                               *)
(*                                                                        *)
(*  Anders Miltner edited it a bit, and is very confused by licenses...   *)
(*  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.) *)

open Util

(* This is to open core for deriving, but keep closed eleswhere*)
module HashConsContainer = struct
  open Core
  type +'a hash_consed =
    {
      hkey : int;
      tag  : int;
      node : 'a;
    }

  let pp_hash_consed
      (npper:'a pper)
      (f:Format.formatter)
      (x:'a hash_consed)
    : unit =
    npper f x.node

  let hash_fold_hash_consed
      (_:'a hash_folder)
      (s:Base__Hash.state)
      (x:'a hash_consed)
    : Base__Hash.state =
    Base__Hash.fold_int s x.tag

  let equal_hash_consed
      (_:'a -> 'a -> bool)
      (x1:'a hash_consed)
      (x2:'a hash_consed)
    : bool =
    x1.tag = x2.tag

  let compare_hash_consed
      (_:'a -> 'a -> int)
      (x1:'a hash_consed)
      (x2:'a hash_consed)
    : int =
    compare x1.tag x2.tag

  let hash_consed_of_sexp
      (_:Ppx_sexp_conv_lib.Sexp.t -> 'a)
      (_:Ppx_sexp_conv_lib.Sexp.t)
    : 'a hash_consed =
    failwith "reimplement using create"

  let sexp_of_hash_consed
      (f:'a -> Ppx_sexp_conv_lib.Sexp.t)
      (x:'a hash_consed)
    : Ppx_sexp_conv_lib.Sexp.t =
    f x.node
end
include HashConsContainer

(* Functorial interface *)
module HashConsTable = struct
  let gentag =
    let r = ref 0 in
    fun () -> incr r; !r

  type 'a t = {
    mutable table : 'a hash_consed Weak.t array;
    mutable totsize : int;             (* sum of the bucket sizes *)
    mutable limit : int;               (* max ratio totsize/table length *)
  }

  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
    let emptybucket = Weak.create 0 in
    { table = Array.make sz emptybucket;
      totsize = 0;
      limit = 3; }

  let clear t =
    let emptybucket = Weak.create 0 in
    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 iter f t =
    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 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)

  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 *)
      fold (fun d () -> add newt d) t ();
      t.table <- newt.table;
      t.limit <- t.limit + 2;
    end

  and add t d =
    let index = d.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 hashcons hfun cmpfun t d =
    let hkey = hfun d land max_int in
    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 hnode = { hkey = hkey; tag = gentag (); node = d } in
        add t hnode;
        hnode
      end else begin
        match Weak.get_copy bucket i with
        | Some v when is_equal (cmpfun v.node d) ->
	        begin match Weak.get bucket i with
            | Some v -> v
            | None -> loop (i+1)
         end
        | Some _ ->
          loop (i+1)
        | _ -> loop (i+1)
      end
    in
    loop 0

  let stats t =
    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

module HashConsOf(D:Data) =
struct
  type t = t_node hash_consed
  and t_node = D.t
  [@@deriving show, hash]

  let compare_t_node = D.compare

  let table = HashConsTable.create 100
  let hashcons = HashConsTable.hashcons hash_t_node compare_t_node table

  let uid
      (x:t)
    : int =
    x.tag
end

module Hmap = struct
end

module Hset = struct
  (*s Sets of integers implemented as Patricia trees, following Chris
      Okasaki and Andrew Gill's paper {\em Fast Mergeable Integer Maps}
      ({\tt\small http://www.cs.columbia.edu/\~{}cdo/papers.html\#ml98maps}).
      Patricia trees provide faster operations than standard library's
      module [Set], and especially very fast [union], [subset], [inter]
      and [diff] operations. *)

  (*s The idea behind Patricia trees is to build a {\em trie} on the
      binary digits of the elements, and to compact the representation
      by branching only one the relevant bits (i.e. the ones for which
      there is at least on element in each subtree). We implement here
      {\em little-endian} Patricia trees: bits are processed from
      least-significant to most-significant. The trie is implemented by
      the following type [t]. [Empty] stands for the empty trie, and
      [Leaf k] for the singleton [k]. (Note that [k] is the actual
      element.) [Branch (m,p,l,r)] represents a branching, where [p] is
      the prefix (from the root of the trie) and [m] is the branching
      bit (a power of 2). [l] and [r] contain the subsets for which the
      branching bit is respectively 0 and 1. Invariant: the trees [l]
      and [r] are not empty. *)

  (*i*)
  type 'a elt = 'a hash_consed
  (*i*)

  type 'a t =
    | Empty
    | Leaf of 'a hash_consed
    | Branch of int * int * 'a t * 'a t

  (*s Example: the representation of the set $\{1,4,5\}$ is
      $$\mathtt{Branch~(0,~1,~Leaf~4,~Branch~(1,~4,~Leaf~1,~Leaf~5))}$$
      The first branching bit is the bit 0 (and the corresponding prefix
      is [0b0], not of use here), with $\{4\}$ on the left and $\{1,5\}$ on the
      right. Then the right subtree branches on bit 2 (and so has a branching
      value of $2^2 = 4$), with prefix [0b01 = 1]. *)

  (*s Empty set and singletons. *)

  let empty = Empty

  let is_empty = function Empty -> true | _ -> false

  let singleton k = Leaf k

  (*s Testing the occurrence of a value is similar to the search in a
      binary search tree, where the branching bit is used to select the
      appropriate subtree. *)

  let zero_bit k m = (k land m) == 0

  let rec mem k = function
    | Empty -> false
    | Leaf j -> k.tag == j.tag
    | Branch (_, m, l, r) -> mem k (if zero_bit k.tag m then l else r)

  (*s The following operation [join] will be used in both insertion and
      union. Given two non-empty trees [t0] and [t1] with longest common
      prefixes [p0] and [p1] respectively, which are supposed to
      disagree, it creates the union of [t0] and [t1]. For this, it
      computes the first bit [m] where [p0] and [p1] disagree and create
      a branching node on that bit. Depending on the value of that bit
      in [p0], [t0] will be the left subtree and [t1] the right one, or
      the converse. Computing the first branching bit of [p0] and [p1]
      uses a nice property of twos-complement representation of integers. *)

  let lowest_bit x = x land (-x)

  let branching_bit p0 p1 = lowest_bit (p0 lxor p1)

  let mask p m = p land (m-1)

  (*s When comparing branching bits, one has to be careful with the sign bit *)
  let unsigned_lt n m = n >= 0 && (m < 0 || n < m)

  let join (p0,t0,p1,t1) =
    let m = branching_bit p0 p1 in
    if zero_bit p0 m then
      Branch (mask p0 m, m, t0, t1)
    else
      Branch (mask p0 m, m, t1, t0)

  (*s Then the insertion of value [k] in set [t] is easily implemented
      using [join].  Insertion in a singleton is just the identity or a
      call to [join], depending on the value of [k].  When inserting in
      a branching tree, we first check if the value to insert [k]
      matches the prefix [p]: if not, [join] will take care of creating
      the above branching; if so, we just insert [k] in the appropriate
      subtree, depending of the branching bit. *)

  let match_prefix k p m = (mask k m) == p

  let add k t =
    let rec ins = function
      | Empty -> Leaf k
      | Leaf j as t ->
	if j.tag == k.tag then t else join (k.tag, Leaf k, j.tag, t)
      | Branch (p,m,t0,t1) as t ->
	if match_prefix k.tag p m then
	  if zero_bit k.tag m then
	    Branch (p, m, ins t0, t1)
	  else
	    Branch (p, m, t0, ins t1)
	else
	  join (k.tag, Leaf k, p, t)
    in
    ins t

  (*s The code to remove an element is basically similar to the code of
      insertion. But since we have to maintain the invariant that both
      subtrees of a [Branch] node are non-empty, we use here the
      ``smart constructor'' [branch] instead of [Branch]. *)

  let branch = function
    | (_,_,Empty,t) -> t
    | (_,_,t,Empty) -> t
    | (p,m,t0,t1)   -> Branch (p,m,t0,t1)

  let remove k t =
    let rec rmv = function
      | Empty -> Empty
      | Leaf j as t -> if k.tag == j.tag then Empty else t
      | Branch (p,m,t0,t1) as t ->
	if match_prefix k.tag p m then
	  if zero_bit k.tag m then
	    branch (p, m, rmv t0, t1)
	  else
	    branch (p, m, t0, rmv t1)
	else
	  t
    in
    rmv t

  (*s One nice property of Patricia trees is to support a fast union
      operation (and also fast subset, difference and intersection
      operations). When merging two branching trees we examine the
      following four cases: (1) the trees have exactly the same
      prefix; (2/3) one prefix contains the other one; and (4) the
      prefixes disagree. In cases (1), (2) and (3) the recursion is
      immediate; in case (4) the function [join] creates the appropriate
      branching. *)

  let rec merge = function
    | Empty, t  -> t
    | t, Empty  -> t
    | Leaf k, t -> add k t
    | t, Leaf k -> add k t
    | (Branch (p,m,s0,s1) as s), (Branch (q,n,t0,t1) as t) ->
      if m == n && match_prefix q p m then
	(* The trees have the same prefix. Merge the subtrees. *)
	Branch (p, m, merge (s0,t0), merge (s1,t1))
      else if unsigned_lt m n && match_prefix q p m then
	(* [q] contains [p]. Merge [t] with a subtree of [s]. *)
	if zero_bit q m then
	  Branch (p, m, merge (s0,t), s1)
        else
	  Branch (p, m, s0, merge (s1,t))
      else if unsigned_lt n m && match_prefix p q n then
	(* [p] contains [q]. Merge [s] with a subtree of [t]. *)
	if zero_bit p n then
	  Branch (q, n, merge (s,t0), t1)
	else
	  Branch (q, n, t0, merge (s,t1))
      else
	(* The prefixes disagree. *)
	join (p, s, q, t)

  let union s t = merge (s,t)

  (*s When checking if [s1] is a subset of [s2] only two of the above
      four cases are relevant: when the prefixes are the same and when the
      prefix of [s1] contains the one of [s2], and then the recursion is
      obvious. In the other two cases, the result is [false]. *)

  let rec subset s1 s2 = match (s1,s2) with
    | Empty, _ -> true
    | _, Empty -> false
    | Leaf k1, _ -> mem k1 s2
    | Branch _, Leaf _ -> false
    | Branch (p1,m1,l1,r1), Branch (p2,m2,l2,r2) ->
      if m1 == m2 && p1 == p2 then
	subset l1 l2 && subset r1 r2
      else if unsigned_lt m2 m1 && match_prefix p1 p2 m2 then
	if zero_bit p1 m2 then
	  subset l1 l2 && subset r1 l2
	else
	  subset l1 r2 && subset r1 r2
      else
	false

  (*s To compute the intersection and the difference of two sets, we
      still examine the same four cases as in [merge]. The recursion is
      then obvious. *)

  let rec inter s1 s2 = match (s1,s2) with
    | Empty, _ -> Empty
    | _, Empty -> Empty
    | Leaf k1, _ -> if mem k1 s2 then s1 else Empty
    | _, Leaf k2 -> if mem k2 s1 then s2 else Empty
    | Branch (p1,m1,l1,r1), Branch (p2,m2,l2,r2) ->
      if m1 == m2 && p1 == p2 then
	merge (inter l1 l2, inter r1 r2)
      else if unsigned_lt m1 m2 && match_prefix p2 p1 m1 then
	inter (if zero_bit p2 m1 then l1 else r1) s2
      else if unsigned_lt m2 m1 && match_prefix p1 p2 m2 then
	inter s1 (if zero_bit p1 m2 then l2 else r2)
      else
	Empty

  let rec diff s1 s2 = match (s1,s2) with
    | Empty, _ -> Empty
    | _, Empty -> s1
    | Leaf k1, _ -> if mem k1 s2 then Empty else s1
    | _, Leaf k2 -> remove k2 s1
    | Branch (p1,m1,l1,r1), Branch (p2,m2,l2,r2) ->
      if m1 == m2 && p1 == p2 then
	merge (diff l1 l2, diff r1 r2)
      else if unsigned_lt m1 m2 && match_prefix p2 p1 m1 then
	if zero_bit p2 m1 then
	  merge (diff l1 s2, r1)
	else
	  merge (l1, diff r1 s2)
      else if unsigned_lt m2 m1 && match_prefix p1 p2 m2 then
	if zero_bit p1 m2 then diff s1 l2 else diff s1 r2
      else
	s1

  (*s All the following operations ([cardinal], [iter], [fold], [for_all],
      [exists], [filter], [partition], [choose], [elements]) are
      implemented as for any other kind of binary trees. *)

  let rec cardinal = function
    | Empty -> 0
    | Leaf _ -> 1
    | Branch (_,_,t0,t1) -> cardinal t0 + cardinal t1

  let rec iter f = function
    | Empty -> ()
    | Leaf k -> f k
    | Branch (_,_,t0,t1) -> iter f t0; iter f t1

  let rec fold f s accu = match s with
    | Empty -> accu
    | Leaf k -> f k accu
    | Branch (_,_,t0,t1) -> fold f t0 (fold f t1 accu)

  let rec for_all p = function
    | Empty -> true
    | Leaf k -> p k
    | Branch (_,_,t0,t1) -> for_all p t0 && for_all p t1

  let rec exists p = function
    | Empty -> false
    | Leaf k -> p k
    | Branch (_,_,t0,t1) -> exists p t0 || exists p t1

  let rec filter pr = function
    | Empty -> Empty
    | Leaf k as t -> if pr k then t else Empty
    | Branch (p,m,t0,t1) -> branch (p, m, filter pr t0, filter pr t1)

  let partition p s =
    let rec part (t,f as acc) = function
      | Empty -> acc
      | Leaf k -> if p k then (add k t, f) else (t, add k f)
      | Branch (_,_,t0,t1) -> part (part acc t0) t1
    in
    part (Empty, Empty) s

  let rec choose = function
    | Empty -> raise Not_found
    | Leaf k -> k
    | Branch (_, _,t0,_) -> choose t0   (* we know that [t0] is non-empty *)

  let elements s =
    let rec elements_aux acc = function
      | Empty -> acc
      | Leaf k -> k :: acc
      | Branch (_,_,l,r) -> elements_aux (elements_aux acc l) r
    in
    elements_aux [] s

  (*s There is no way to give an efficient implementation of [min_elt]
      and [max_elt], as with binary search trees.  The following
      implementation is a traversal of all elements, barely more
      efficient than [fold min t (choose t)] (resp. [fold max t (choose
      t)]). Note that we use the fact that there is no constructor
      [Empty] under [Branch] and therefore always a minimal
      (resp. maximal) element there. *)

  let rec min_elt = function
    | Empty -> raise Not_found
    | Leaf k -> k
    | Branch (_,_,s,t) -> min (min_elt s) (min_elt t)

  let rec max_elt = function
    | Empty -> raise Not_found
    | Leaf k -> k
    | Branch (_,_,s,t) -> max (max_elt s) (max_elt t)

  (*s Another nice property of Patricia trees is to be independent of the
      order of insertion. As a consequence, two Patricia trees have the
      same elements if and only if they are structurally equal. *)

  let equal = (=)

  let compare = compare

  (*i*)
  let make l = List.fold_right add l empty
  (*i*)

  (*s Additional functions w.r.t to [Set.S]. *)

  let rec intersect s1 s2 = match (s1,s2) with
    | Empty, _ -> false
    | _, Empty -> false
    | Leaf k1, _ -> mem k1 s2
    | _, Leaf k2 -> mem k2 s1
    | Branch (p1,m1,l1,r1), Branch (p2,m2,l2,r2) ->
      if m1 == m2 && p1 == p2 then
        intersect l1 l2 || intersect r1 r2
      else if unsigned_lt m1 m2 && match_prefix p2 p1 m1 then
        intersect (if zero_bit p2 m1 then l1 else r1) s2
      else if unsigned_lt m2 m1 && match_prefix p1 p2 m2 then
        intersect s1 (if zero_bit p1 m2 then l2 else r2)
      else
        false
end