diff --git a/src/lib_stdlib/hashPtree.ml b/src/lib_stdlib/hashPtree.ml
new file mode 100644
index 000000000..3de6865f5
--- /dev/null
+++ b/src/lib_stdlib/hashPtree.ml
@@ -0,0 +1,1051 @@
+(**************************************************************************)
+(*                                                                        *)
+(*    Copyright (c) 2014 - 2017.                                          *)
+(*    Dynamic Ledger Solutions, Inc. <contact@tezos.com>                  *)
+(*                                                                        *)
+(*    All rights reserved. No warranty, explicit or implicit, provided.   *)
+(*                                                                        *)
+(**************************************************************************)
+
+module Ptree_sig = struct
+  module type Value = sig
+
+    type t
+    val equal : t -> t -> bool
+    val hash : t -> int
+
+  end
+
+  type prefix_order =
+    | Equal
+    | Shorter
+    | Longer
+    | Different
+
+  module type Prefix = sig
+    type key    (* bit sequence *)
+    type prefix (* prefix of a bit sequence *)
+    type mask   (* integer length of a bit sequence *)
+
+    val equal_key : key -> key -> bool
+    val equal_mask : mask -> mask -> bool
+    val equal_prefix : prefix -> prefix -> bool
+
+    val hash_key : key -> int
+    val hash_mask : mask -> int
+    val hash_prefix : prefix -> int
+
+    val full_length_mask : mask
+
+    val strictly_shorter_mask : mask -> mask -> bool
+
+    val key_prefix : key -> prefix
+    (* Full lenght prefix *)
+    val prefix_key : prefix -> mask -> key
+    (* Some key matching the prefix with the given mask *)
+
+    val match_prefix : key:key -> prefix:prefix -> mask:mask -> bool
+    (* Does the prefix of length [mask] of [key] equals to [prefix] *)
+
+    val select_bit : prefix:prefix -> mask:mask -> bool
+    (* Get the bit of [prefix] at position [mask] assumes that [mask] is
+       less than the length of prefix *)
+
+    val common_mask : prefix -> prefix -> mask
+    (* The length of the common part of given prefixes *)
+
+    val apply_mask : prefix -> mask -> prefix
+    (* Cut the prefix to the given length *)
+
+    val compare_prefix : mask -> prefix -> mask -> prefix -> prefix_order
+    (* [compare_prefix m1 p1 m2 p2]:
+       let p1' (resp p2') be the sub-prefix of length m1 of p1 (resp m2 of p2)
+       The result is
+         Equal if p1' equal p2'
+         Shorter if p1' is a prefix of p2'
+         Longer if p2' is a prefix of p1'
+         Different if those not ordered
+    *)
+  end
+
+  module type S = sig
+
+    type key
+    type prefix
+    type mask
+    type value
+
+    type not_empty = TNot_empty
+    type empty     = TEmpty
+
+    type _ t = private
+      | Leaf : {
+          mutable id: int; (* Mutable to get a good sharing semantics *)
+          mask : mask;
+          key : key;
+          value : value;
+        } -> not_empty t
+      | Node : {
+          mutable id : int;
+          mask : mask;
+          prefix : prefix;
+          true_ : not_empty t;
+          false_ : not_empty t;
+        } -> not_empty t
+      | Empty : empty t
+
+    val leaf : key:key -> mask:mask -> value -> not_empty t
+    val node : prefix:prefix -> mask:mask -> true_:not_empty t -> false_:not_empty t -> not_empty t
+    val empty : empty t
+
+    val equal : 'a t -> 'b t -> bool
+
+    val fast_partial_equal : 'a t -> 'b t -> bool
+    (* if [fast_partial_equal x y] is true, then [equal x y] is true,
+       but if fast_partial_equal returns false, nothing can be
+       asserted. *)
+
+    val id : not_empty t -> int
+  end
+end
+
+module Shared_tree : sig
+
+  module Hash_consed_tree(P:Ptree_sig.Prefix)(V:Ptree_sig.Value) : Ptree_sig.S
+    with type value = V.t
+     and type key = P.key
+     and type prefix = P.prefix
+     and type mask = P.mask
+
+  module Simple_tree(P:Ptree_sig.Prefix)(V:sig type t val equal : t -> t -> bool  end) : Ptree_sig.S
+    with type value = V.t
+     and type key = P.key
+     and type prefix = P.prefix
+     and type mask = P.mask
+
+end = struct
+  open Ptree_sig
+
+(*
+  type int2 = { mutable i1 : int; mutable i2 : int }
+  let h2 = { i1 = 0; i2 = 0 }
+  let hash2int x1 x2 =
+    h2.i1 <- x1; h2.i2 <- x2;
+    Hashtbl.hash h2
+*)
+  type int3 = { mutable i1 : int; mutable i2 : int; mutable i3 : int }
+  let h3 = { i1 = 0; i2 = 0; i3 = 0 }
+  let hash3int x1 x2 x3 =
+    h3.i1 <- x1; h3.i2 <- x2; h3.i3 <- x3;
+    Hashtbl.hash h3
+
+  type int4 = { mutable i1 : int; mutable i2 : int; mutable i3 : int; mutable i4 : int }
+  let h4 = { i1 = 0; i2 = 0; i3 = 0; i4 = 0 }
+  let hash4int x1 x2 x3 x4 =
+    h4.i1 <- x1; h4.i2 <- x2; h4.i3 <- x3; h4.i4 <- x4;
+    Hashtbl.hash h4
+
+
+  module Hash_consed_tree(P:Prefix)(V:Value) : S
+    with type value = V.t
+     and type key = P.key
+     and type prefix = P.prefix
+     and type mask = P.mask
+  = struct
+
+    type key = P.key
+    type mask = P.mask
+    type prefix = P.prefix
+    type value = V.t
+
+    type not_empty = TNot_empty
+    type empty     = TEmpty
+
+    type _ t =
+      | Leaf : {
+          mutable id: int; (* Mutable to get a good sharing semantics *)
+          mask : mask;
+          key : key;
+          value : value;
+        } -> not_empty t
+      | Node : {
+          mutable id : int;
+          mask : mask;
+          prefix : prefix;
+          true_ : not_empty t;
+          false_ : not_empty t;
+        } -> not_empty t
+      | Empty : empty t
+
+    let id : not_empty t -> int = function
+      | Leaf { id ; _ } -> id
+      | Node { id ; _ } -> id
+
+    let set_id (n : not_empty t) id = match n with
+      | Leaf r -> r.id <- id
+      | Node r -> r.id <- id
+
+    (*let mask : not_empty t -> mask = function
+      | Leaf { mask ; _ } -> mask
+      | Node { mask ; _ } -> mask
+    *)
+    (* let prefix_table = WeakPrefixTbl.create 20 *)
+
+    module Tree :
+      Hashtbl.HashedType with type t = not_empty t
+    = struct
+
+      type nonrec t = not_empty t
+
+      let equal (t1 : t) (t2 : t) = match t1, t2 with
+        | Leaf _, Node _ | Node _, Leaf _-> false
+        | Leaf { key = p1; value = v1; mask = m1 ; _ },
+          Leaf { key = p2; value = v2; mask = m2 ; _ } ->
+            P.equal_key p1 p2 && P.equal_mask m1 m2 && V.equal v1 v2
+        | Node { prefix = p1; mask = m1; true_ = t1; false_ = f1 ; _ },
+          Node { prefix = p2; mask = m2; true_ = t2; false_ = f2 ; _ } ->
+            (* Assumes that only the head can be unshared: this means
+               that structural equality implies physical one on children *)
+            P.equal_prefix p1 p2 &&
+            P.equal_mask m1 m2 && t1 == t2 && f1 == f2
+
+      let hash : t -> int = function
+        | Leaf { key; value; mask ; _ } ->
+            hash3int (P.hash_key key) (V.hash value) (P.hash_mask mask)
+        | Node { mask; prefix; true_; false_ ; _ } ->
+            hash4int
+              (P.hash_mask mask) (P.hash_prefix prefix)
+              (id true_) (id false_)
+
+    end
+
+    module WeakTreeTbl = Weak.Make(Tree)
+
+    (* Or move that to a state ? *)
+    let weak_tree_tbl = WeakTreeTbl.create 10
+
+    let next =
+      let r = ref 0 in
+      fun () -> incr r; !r
+
+    let leaf ~key ~mask value =
+      let l = Leaf { id = 0; key; value; mask } in
+      match WeakTreeTbl.find weak_tree_tbl l with
+      | exception Not_found ->
+          set_id l (next ());
+          WeakTreeTbl.add weak_tree_tbl l;
+          l
+      | l -> l
+
+    let node ~prefix ~mask ~true_ ~false_ =
+      let l = Node { id = 0; mask; prefix; true_; false_ } in
+      match WeakTreeTbl.find weak_tree_tbl l with
+      | exception Not_found ->
+          set_id l (next ());
+          WeakTreeTbl.add weak_tree_tbl l;
+          l
+      | l -> l
+
+    let empty = Empty
+
+    (* Is there a better way to do ? *)
+    let equal (x:'a t) (y:'b t) =
+      (Obj.magic x) == (Obj.magic y)
+
+    let fast_partial_equal = equal
+
+  end [@@inline]
+
+  module Simple_tree(P:Ptree_sig.Prefix)(V:sig type t val equal : t -> t -> bool end) : S
+    with type value = V.t
+     and type key = P.key
+     and type prefix = P.prefix
+     and type mask = P.mask
+  = struct
+
+    type key = P.key
+    type mask = P.mask
+    type prefix = P.prefix
+    type value = V.t
+
+    type not_empty = TNot_empty
+    type empty     = TEmpty
+
+    type _ t =
+      | Leaf : {
+          mutable id: int; (* Mutable to get a good sharing semantics *)
+          mask : mask;
+          key : key;
+          value : value;
+        } -> not_empty t
+      | Node : {
+          mutable id : int;
+          mask : mask;
+          prefix : prefix;
+          true_ : not_empty t;
+          false_ : not_empty t;
+        } -> not_empty t
+      | Empty : empty t
+
+    let id : not_empty t -> int = function
+      | Leaf { id ; _ } -> id
+      | Node { id ; _ } -> id
+
+    (*let set_id (n : not_empty t) id = match n with
+      | Leaf r -> r.id <- id
+      | Node r -> r.id <- id
+
+      let mask : not_empty t -> mask = function
+      | Leaf { mask ; _ } -> mask
+      | Node { mask ; _ } -> mask
+    *)
+    let leaf ~key ~mask value =
+      Leaf { id = 0; key; value; mask }
+
+    let node ~prefix ~mask ~true_ ~false_ =
+      Node { id = 0; mask; prefix; true_; false_ }
+
+    let empty = Empty
+
+    let rec equal_not_empty (x:not_empty t) (y:not_empty t) =
+      x == y ||
+      match x, y with
+      | Leaf l1, Leaf l2 ->
+          P.equal_key l1.key l2.key &&
+          V.equal l1.value l2.value
+      | Node n1, Node n2 ->
+          P.equal_prefix n1.prefix n2.prefix &&
+          P.equal_mask n1.mask n2.mask &&
+          equal_not_empty n1.true_ n2.true_ &&
+          equal_not_empty n1.false_ n2.false_
+      | Node _, Leaf _ | Leaf _, Node _ -> false
+
+    let equal : type a b. a t -> b t -> bool = fun x y ->
+      match x, y with
+      | Empty, Empty -> true
+      | Leaf _, Leaf _ ->
+          equal_not_empty x y
+      | Node _, Node _ ->
+          equal_not_empty x y
+      | _, _ ->
+          false
+
+    let fast_partial_equal (x:'a t) (y:'b t) =
+      (Obj.magic x) == (Obj.magic y)
+
+  end [@@inline]
+
+end
+
+module type Value = sig
+  type t
+  val equal : t -> t -> bool
+  val hash : t -> int
+end
+
+module type Bits = sig
+  type t
+
+  val lnot : t -> t
+  val (land) : t -> t -> t
+  val (lxor) : t -> t -> t
+  val (lor) : t -> t -> t
+  val (lsr) : t -> int -> t
+  val (lsl) : t -> int -> t
+  val pred : t -> t
+
+  val less_than : t -> t -> bool
+
+  val highest_bit : t -> t
+  val equal : t -> t -> bool
+  val hash : t -> int
+  val zero : t
+  val one : t
+
+  val size : int
+end
+
+module type Size = sig
+  val size : int
+end
+
+module Bits(S:Size) = struct
+  type t = Z.t
+  let size = S.size
+  let higher_bit = Z.shift_left Z.one size
+  let mask = Z.pred higher_bit
+
+  let mark n = Z.logor higher_bit n
+  let unmark n = Z.logxor higher_bit n
+
+  let one = mark Z.one
+  let zero = higher_bit
+  let hash = Z.hash
+  let equal = Z.equal
+  let less_than = Z.lt
+
+  let highest_bit_unmarked n =
+    if Z.equal Z.zero n then
+      Z.zero
+    else
+      Z.(Z.one lsl (Pervasives.pred (numbits n)))
+
+  let highest_bit n = mark (highest_bit_unmarked (unmark n))
+
+  let lnot x = Z.logor (Z.lognot x) higher_bit
+  let (land) = Z.logand
+  let (lxor) a b = Z.logor (Z.logxor a b) higher_bit
+  let (lor) = Z.logor
+  let (lsr) a n =
+    Z.logor
+      (Z.shift_right_trunc (Z.logxor a higher_bit) n)
+      higher_bit
+  let (lsl) a n =
+    Z.logor
+      (Z.logand (Z.shift_left a n) mask)
+      higher_bit
+
+  let pred = Z.pred
+
+  let of_z n = mark n
+  let to_z n = unmark n
+end
+
+module BE_gen_prefix(Bits:Bits) : Ptree_sig.Prefix
+  with type key = Bits.t
+   and type prefix = Bits.t
+   and type mask = Bits.t
+= struct
+  type key = Bits.t
+  type mask = Bits.t (* Only a single bit set *)
+  type prefix = Bits.t
+
+  let equal_key = Bits.equal
+  let equal_mask = Bits.equal
+  let equal_prefix = Bits.equal
+
+  let hash_key x = Bits.hash x
+  let hash_mask x = Bits.hash x
+  let hash_prefix x = Bits.hash x
+
+  open Bits
+
+  let full_length_mask = Bits.one
+
+  let strictly_shorter_mask (m1:mask) m2 =
+    Bits.less_than m2 m1
+
+  let select_bit ~prefix ~mask =
+    not (Bits.equal (prefix land mask) Bits.zero)
+
+  let apply_mask prefix mask =
+    prefix land (lnot (pred mask))
+
+  let match_prefix ~key ~prefix ~mask =
+    equal_prefix (apply_mask key mask) prefix
+
+  let common_mask p0 p1 =
+    (Bits.highest_bit (* [@inlined] *)) (p0 lxor p1)
+
+  let key_prefix x = x
+  let prefix_key p _m = p
+
+  let smaller_set_mask m1 m2 =
+    (lnot (pred m1))
+    land
+    (lnot (pred m2))
+
+  let compare_prefix m1 p1 m2 p2 =
+    let min_mask = smaller_set_mask m1 m2 in
+    let applied_p1 = p1 land min_mask in
+    let applied_p2 = p2 land min_mask in
+    if applied_p1 = applied_p2 then
+      if m1 > m2 then Ptree_sig.Shorter
+      else if m1 < m2 then Ptree_sig.Longer
+      else Ptree_sig.Equal
+    else
+      Ptree_sig.Different
+end
+
+
+module LE_prefix : Ptree_sig.Prefix
+  with type key = int
+   and type prefix = int
+   and type mask = int
+= struct
+  type key = int
+  type mask = int (* Only a single bit set *)
+  type prefix = int
+
+  let equal_key = (==)
+  let equal_mask = (==)
+  let equal_prefix = (==)
+
+  let hash_key x = x
+  let hash_mask x = x
+  let hash_prefix x = x
+
+  let full_length_mask = (-1) lxor ((-1) lsr 1)
+
+  let strictly_shorter_mask (m1:mask) m2 =
+    m1 < m2
+
+  let select_bit ~prefix ~mask = (prefix land mask) != 0
+
+  let apply_mask prefix mask = prefix land (mask-1)
+  let match_prefix ~key ~prefix ~mask =
+    (apply_mask key mask) == prefix
+
+  let lowest_bit x = x land (-x)
+  let common_mask p0 p1 = lowest_bit (p0 lxor p1)
+
+  let key_prefix x = x
+  let prefix_key p _m = p
+
+  let smaller_set_mask m1 m2 = (m1-1) land (m2-1)
+
+  let compare_prefix m1 p1 m2 p2 =
+    let min_mask = smaller_set_mask m1 m2 in
+    let applied_p1 = p1 land min_mask in
+    let applied_p2 = p2 land min_mask in
+    if applied_p1 = applied_p2 then
+      if m1 < m2 then Ptree_sig.Shorter
+      else if m1 > m2 then Ptree_sig.Longer
+      else Ptree_sig.Equal
+    else
+      Ptree_sig.Different
+end
+
+module BE_prefix : Ptree_sig.Prefix
+  with type key = int
+   and type prefix = int
+   and type mask = int
+= struct
+  type key = int
+  type mask = int (* Only a single bit set *)
+  type prefix = int
+
+  let equal_key = (==)
+  let equal_mask = (==)
+  let equal_prefix = (==)
+
+  let hash_key x = x
+  let hash_mask x = x
+  let hash_prefix x = x
+
+  let full_length_mask = 1
+
+  let strictly_shorter_mask (m1:mask) m2 =
+    m1 > m2
+
+  let select_bit ~prefix ~mask = (prefix land mask) != 0
+
+  module Nativeint_infix = struct
+    let (lor) = Nativeint.logor
+    (*let (lsl) = Nativeint.shift_left*)
+    let (lsr) = Nativeint.shift_right_logical
+    (*let (asr) = Nativeint.shift_right*)
+    let (land) = Nativeint.logand
+    let (lnot) = Nativeint.lognot
+    let (lxor) = Nativeint.logxor
+    let (-) = Nativeint.sub
+  end
+
+  let apply_mask prefix mask =
+    let open Nativeint_infix in
+    let prefix = Nativeint.of_int prefix in
+    let mask = Nativeint.of_int mask in
+    Nativeint.to_int
+      (
+        prefix land
+        (lnot (mask - 1n))
+      )
+
+  let match_prefix ~key ~prefix ~mask =
+    (apply_mask key mask) == prefix
+
+  let highest_bit x =
+    Nativeint_infix.(
+      let x = x lor (x lsr 1) in
+      let x = x lor (x lsr 2) in
+      let x = x lor (x lsr 4) in
+      let x = x lor (x lsr 8) in
+      let x = x lor (x lsr 16) in
+      let x =
+        if Sys.word_size > 32 then
+          x lor (x lsr 32)
+        else
+          x
+      in
+      Nativeint.to_int (x - (x lsr 1))
+    )
+
+  let common_mask p0 p1 =
+    let open Nativeint_infix in
+    let p0 = Nativeint.of_int p0 in
+    let p1 = Nativeint.of_int p1 in
+    highest_bit (p0 lxor p1)
+
+  let key_prefix x = x
+  let prefix_key p _m = p
+
+  let smaller_set_mask m1 m2 =
+    let open Nativeint_infix in
+    (lnot (m1 - 1n))
+    land
+    (lnot (m2 - 1n))
+
+  let compare_prefix m1 p1 m2 p2 =
+    let open Nativeint_infix in
+    let m1 = Nativeint.of_int m1 in
+    let m2 = Nativeint.of_int m2 in
+    let p1 = Nativeint.of_int p1 in
+    let p2 = Nativeint.of_int p2 in
+    let min_mask = smaller_set_mask m1 m2 in
+    let applied_p1 = p1 land min_mask in
+    let applied_p2 = p2 land min_mask in
+    if applied_p1 = applied_p2 then
+      if m1 > m2 then Ptree_sig.Shorter
+      else if m1 < m2 then Ptree_sig.Longer
+      else Ptree_sig.Equal
+    else
+      Ptree_sig.Different
+end
+
+module Make(P:Ptree_sig.Prefix)(V:Value) = struct
+
+  module T = Shared_tree.Hash_consed_tree(P)(V)
+
+  type t = E : 'a T.t -> t [@@ocaml.unboxed]
+  type key = T.key
+  type value = T.value
+  type mask = T.mask
+(*
+  let (=) = `Do_not_use_polymorphic_equality
+  let (<=) = `Do_not_use_polymorphic_comparison
+  let (>=) = `Do_not_use_polymorphic_comparison
+  let (<) = `Do_not_use_polymorphic_comparison
+  let (>) = `Do_not_use_polymorphic_comparison
+  let compare = `Do_not_use_polymorphic_comparison
+   *)
+  let equal (E t1) (E t2) = T.equal t1 t2
+
+  let select_key_bit k m =
+    P.select_bit ~prefix:(P.key_prefix k) ~mask:m
+
+  let matching_key k1 k2 mask =
+    let p1 = P.apply_mask (P.key_prefix k1) mask in
+    let p2 = P.apply_mask (P.key_prefix k2) mask in
+    P.equal_prefix p1 p2
+
+  let rec mem : type k. key -> k T.t -> bool = fun k -> function
+    | T.Empty ->
+        false
+    | T.Leaf { key; mask ; _} ->
+        matching_key key k mask
+    | T.Node { prefix = _; mask; true_; false_ ; _ } ->
+        mem k
+          (if select_key_bit k mask then true_ else false_)
+
+  let rec mem_exact : type k. key -> k T.t -> bool = fun k -> function
+    | T.Empty ->
+        false
+    | T.Leaf { key; mask ; _ } ->
+        P.equal_key k key && P.equal_mask mask P.full_length_mask
+    | T.Node { prefix = _; mask; true_; false_ ; _ } ->
+        mem_exact k
+          (if select_key_bit k mask then true_ else false_)
+
+  let rec find_ne k (t: T.not_empty T.t) = match t with
+    | T.Leaf { key; value; mask ; _ } ->
+        if matching_key key k mask then
+          Some value
+        else
+          None
+    | T.Node { prefix = _; mask; true_; false_ ; _ } ->
+        find_ne k
+          (if select_key_bit k mask then true_ else false_)
+
+  let find : type k. key -> k T.t -> value option = fun k -> function
+    | T.Empty ->
+        None
+    | T.Leaf _ as t ->
+        find_ne k t
+    | T.Node _ as t ->
+        find_ne k t
+
+  let singleton ~key ~value ~mask =
+    T.leaf ~key value ~mask
+
+  let join ~mask p0 t0 p1 t1 =
+    (* assumes p0 <> p1 *)
+    let c_mask = P.common_mask p0 p1 in
+    let mask = if P.strictly_shorter_mask c_mask mask then c_mask else mask in
+    let prefix = P.apply_mask p1 mask in
+    let true_, false_ =
+      if P.select_bit ~prefix:p0 ~mask then
+        t0, t1
+      else
+        t1, t0
+    in
+    T.node ~prefix ~mask ~true_ ~false_
+
+  let rebuild_ne_branch node prefix mask ~node_true ~node_false ~true_ ~false_ =
+    if T.fast_partial_equal node_true true_ &&
+       T.fast_partial_equal node_false false_ then
+      node
+    else
+      T.node ~prefix ~mask ~true_ ~false_
+
+  let rec add_ne combine ~key ~value ?(mask=P.full_length_mask) t =
+    match t with
+    | T.Leaf leaf ->
+        if P.equal_key key leaf.key && P.equal_mask leaf.mask P.full_length_mask then
+          if value == leaf.value then
+            t
+          else
+            T.leaf ~key (combine value leaf.value) ~mask
+        else if
+          P.strictly_shorter_mask leaf.mask mask &&
+          P.match_prefix ~key ~prefix:(P.key_prefix leaf.key) ~mask:leaf.mask then
+          (* The previous leaf shadows the new one: no modification *)
+          t
+        else if
+          P.strictly_shorter_mask mask leaf.mask &&
+          P.match_prefix ~key:leaf.key ~prefix:(P.key_prefix key) ~mask then
+          (* The new leaf shadows the previous one: replace *)
+          T.leaf ~key (combine value leaf.value) ~mask
+        else
+          join ~mask
+            (P.key_prefix key) (T.leaf ~key value ~mask)
+            (P.key_prefix leaf.key) t
+    | T.Node node ->
+        if P.match_prefix ~key ~prefix:node.prefix ~mask:node.mask then
+          let true_, false_ =
+            if select_key_bit key node.mask then
+              add_ne combine ~key ~value ~mask node.true_, node.false_
+            else
+              node.true_, add_ne combine ~key ~value ~mask node.false_
+          in
+          rebuild_ne_branch t node.prefix node.mask
+            ~node_false:node.false_ ~node_true:node.true_
+            ~true_ ~false_
+        else
+          join ~mask
+            (P.key_prefix key) (T.leaf ~key value ~mask)
+            node.prefix t
+
+  let add : type k.
+    (value -> value -> value) -> key:key -> value:value ->
+    ?mask:P.mask -> k T.t ->
+    T.not_empty T.t = fun combine ~key ~value ?(mask=P.full_length_mask) ->
+    function
+    | T.Empty ->
+        singleton ~key ~value ~mask
+
+    (* Should be merged by matcher *)
+    | T.Leaf _ as t ->
+        add_ne combine ~key ~value ~mask t
+    | T.Node _ as t ->
+        add_ne combine ~key ~value ~mask t
+
+  let empty = E T.empty
+
+  let rebuild_branch
+      node prefix mask ~node_true ~node_false
+      ~true_:(E true_) ~false_:(E false_) =
+    match true_, false_ with
+    | T.Empty, T.Empty ->
+        empty
+    | T.Empty, t ->
+        E t
+    | t, T.Empty ->
+        E t
+    | T.Leaf _ as true_, (T.Leaf _ as false_) ->
+        E (rebuild_ne_branch node prefix mask ~node_true ~node_false ~true_ ~false_)
+    | T.Leaf _ as true_, (T.Node _ as false_) ->
+        E (rebuild_ne_branch node prefix mask ~node_true ~node_false ~true_ ~false_)
+    | T.Node _ as true_, (T.Leaf _ as false_) ->
+        E (rebuild_ne_branch node prefix mask ~node_true ~node_false ~true_ ~false_)
+    | T.Node _ as true_, (T.Node _ as false_) ->
+        E (rebuild_ne_branch node prefix mask ~node_true ~node_false ~true_ ~false_)
+
+  let rec remove_ne : key -> T.not_empty T.t -> t =
+    fun key t ->
+      match t with
+      | T.Leaf leaf ->
+          if matching_key leaf.key key leaf.mask then
+            E T.empty
+          else
+            E t
+      | T.Node node ->
+          if P.match_prefix ~key ~prefix:node.prefix ~mask:node.mask then
+            let true_, false_ =
+              if select_key_bit key node.mask then
+                remove_ne key node.true_, E node.false_
+              else
+                E node.true_, remove_ne key node.false_
+            in
+            rebuild_branch t node.prefix node.mask
+              ~node_true:node.true_ ~node_false:node.false_ ~true_ ~false_
+          else
+            E t
+
+  let remove key (E t) =
+    match t with
+    | T.Empty ->
+        empty
+    | T.Leaf _ as t ->
+        remove_ne key t
+    | T.Node _ as t ->
+        remove_ne key t
+
+  let rec remove_prefix_ne : key -> mask -> T.not_empty T.t -> t =
+    fun key mask t ->
+      match t with
+      | T.Leaf leaf ->
+          if matching_key key leaf.key mask then
+            E T.empty
+          else
+            E t
+      | T.Node node ->
+          match P.compare_prefix mask (P.key_prefix key) node.mask node.prefix with
+          | Different ->
+              E t
+          | Equal ->
+              E T.empty
+          | Shorter ->
+              E T.empty
+          | Longer ->
+              let true_, false_ =
+                if select_key_bit key node.mask then
+                  remove_prefix_ne key mask node.true_, E node.false_
+                else
+                  E node.true_, remove_prefix_ne key mask node.false_
+              in
+              rebuild_branch t node.prefix node.mask
+                ~node_true:node.true_ ~node_false:node.false_ ~true_ ~false_
+
+  let remove_prefix key mask (E t) =
+    match t with
+    | T.Empty ->
+        empty
+    | T.Leaf _ as t ->
+        remove_prefix_ne key mask t
+    | T.Node _ as t ->
+        remove_prefix_ne key mask t
+
+  let rec remove_ne_exact : key -> T.not_empty T.t -> t =
+    fun key t ->
+      match t with
+      | T.Leaf leaf ->
+          if P.equal_key leaf.key key && P.equal_mask leaf.mask P.full_length_mask then
+            E T.empty
+          else
+            E t
+      | T.Node node ->
+          if P.match_prefix ~key ~prefix:node.prefix ~mask:node.mask then
+            let true_, false_ =
+              if select_key_bit key node.mask then
+                remove_ne_exact key node.true_, E node.false_
+              else
+                E node.true_, remove_ne_exact key node.false_
+            in
+            rebuild_branch t node.prefix node.mask
+              ~node_true:node.true_ ~node_false:node.false_ ~true_ ~false_
+          else
+            E t
+
+  let remove_exact key (E t) =
+    match t with
+    | T.Empty ->
+        empty
+    | T.Leaf _ as t ->
+        remove_ne_exact key t
+    | T.Node _ as t ->
+        remove_ne_exact key t
+
+  let rec replace_subtree_ne ~key ~id value t =
+    match t with
+    | T.Leaf leaf ->
+        if leaf.id == id then
+          T.leaf ~key:leaf.key ~mask:leaf.mask value
+        else
+          t
+    | T.Node node ->
+        if node.id == id then
+          T.leaf ~key:(P.prefix_key node.prefix node.mask) ~mask:node.mask value
+        else
+        if P.match_prefix ~key ~prefix:node.prefix ~mask:node.mask then
+          let true_, false_ =
+            if select_key_bit key node.mask then
+              replace_subtree_ne ~key ~id value node.true_, node.false_
+            else
+              node.true_, replace_subtree_ne ~key ~id value node.false_
+          in
+          rebuild_ne_branch t node.prefix node.mask
+            ~node_true:node.true_ ~node_false:node.false_ ~true_ ~false_
+        else
+          t
+
+  let replace_subtree ~replaced:(E replaced) value t =
+    let replace_subtree_aux ~key ~id value (E t) =
+      match t with
+      | T.Empty ->
+          empty
+      | T.Leaf _ as t ->
+          E (replace_subtree_ne ~key ~id value t)
+      | T.Node _ as t ->
+          E (replace_subtree_ne ~key ~id value t)
+    in
+    match replaced with
+    | T.Empty ->
+        t
+    | T.Leaf leaf ->
+        replace_subtree_aux ~key:leaf.key ~id:leaf.id value t
+    | T.Node node ->
+        replace_subtree_aux
+          ~key:(P.prefix_key node.prefix node.mask)
+          ~id:node.id value t
+
+
+  let rec fold_ne : (key -> mask -> value -> 'a -> 'a) -> T.not_empty T.t -> 'a -> 'a =
+    fun f t acc ->
+      match t with
+      | T.Leaf {key; mask; value; _} ->
+          f key mask value acc
+      | T.Node node ->
+          let acc = fold_ne f node.false_ acc in
+          fold_ne f node.true_ acc
+
+  let fold f (E t) acc =
+    match t with
+    | T.Empty ->
+        acc
+    | T.Leaf _ as t ->
+        fold_ne f t acc
+    | T.Node _ as t ->
+        fold_ne f t acc
+
+  module T_id = struct
+    type t = T.not_empty T.t
+
+    let hash = T.id
+    let equal t1 t2 = T.id t1 == T.id t2
+  end
+  module Map_cache = Ephemeron.K1.Make(T_id)
+
+  module type Map_Reduce = sig
+    type result
+    val default : result
+    val map : t -> key -> T.value -> result
+    val reduce : t -> result -> result -> result
+  end
+  module Map_Reduce(M:Map_Reduce) = struct
+    let cache : M.result Map_cache.t = Map_cache.create 10
+
+    let rec map_reduce_ne t =
+      match Map_cache.find cache t with
+      | v -> v
+      | exception Not_found ->
+          let v =
+            match t with
+            | T.Leaf leaf ->
+                M.map (E t) leaf.key leaf.value
+            | T.Node node ->
+                let v_true = map_reduce_ne node.true_ in
+                let v_false = map_reduce_ne node.false_ in
+                M.reduce (E t) v_true v_false
+          in
+          Map_cache.add cache t v;
+          v
+
+    let run (E t) = match t with
+      | T.Empty ->
+          M.default
+      | T.Leaf _ as t ->
+          map_reduce_ne t
+      | T.Node _ as t ->
+          map_reduce_ne t
+
+    let rec filter_ne f t =
+      let result = map_reduce_ne t in
+      if f result then
+        E t
+      else
+        match t with
+        | T.Leaf _ ->
+            empty
+        | T.Node node ->
+            let true_ = filter_ne f node.true_ in
+            let false_ = filter_ne f node.false_ in
+            rebuild_branch t node.prefix node.mask
+              ~node_true:node.true_ ~node_false:node.false_ ~true_ ~false_
+
+    let filter f (E t) = match t with
+      | T.Empty ->
+          empty
+      | T.Leaf _ as t ->
+          filter_ne f t
+      | T.Node _ as t ->
+          filter_ne f t
+
+  end
+
+  (* Packing in the existential *)
+
+  let mem key (E t) =
+    mem key t
+
+  let mem_exact key (E t) =
+    mem_exact key t
+
+  let find key (E t) =
+    find key t
+
+  let singleton ~key ~value ~mask =
+    E (singleton ~key ~value ~mask)
+
+  let add combine ~key ~value ?mask (E t) =
+    E (add combine ~key ~value ?mask t)
+
+end [@@inline]
+
+module type S = sig
+  type key
+  type value
+  type mask
+  type t
+
+  val equal : t -> t -> bool
+
+  val empty : t
+  val singleton : key:key -> value:value -> mask:mask -> t
+  val add : (value -> value -> value) -> key:key -> value:value ->
+    ?mask:mask -> t -> t
+  val remove : key -> t -> t
+  val remove_exact : key -> t -> t
+  val remove_prefix : key -> mask -> t -> t
+  val mem : key -> t -> bool
+  val mem_exact : key -> t -> bool
+  val find : key -> t -> value option
+  val replace_subtree : replaced:t -> value -> t -> t
+  val fold : (key -> mask -> value -> 'a -> 'a) -> t -> 'a -> 'a
+
+  module type Map_Reduce = sig
+    type result
+    val default : result
+    val map : t -> key -> value -> result
+    val reduce : t -> result -> result -> result
+  end
+  module Map_Reduce(M:Map_Reduce) : sig
+    val run : t -> M.result
+    val filter : (M.result -> bool) -> t -> t
+  end
+
+end
+
+module Make_LE(V:Value) = Make(LE_prefix)(V)
+module Make_BE(V:Value) = Make(BE_prefix)(V)
+module Make_BE_gen(V:Value)(B:Bits) = Make(BE_gen_prefix(B))(V)
+module Make_BE_sized(V:Value)(S:Size) = Make(BE_gen_prefix(Bits(S)))(V)
diff --git a/src/lib_stdlib/hashPtree.mli b/src/lib_stdlib/hashPtree.mli
new file mode 100644
index 000000000..a15968155
--- /dev/null
+++ b/src/lib_stdlib/hashPtree.mli
@@ -0,0 +1,129 @@
+(**************************************************************************)
+(*                                                                        *)
+(*    Copyright (c) 2014 - 2017.                                          *)
+(*    Dynamic Ledger Solutions, Inc. <contact@tezos.com>                  *)
+(*                                                                        *)
+(*    All rights reserved. No warranty, explicit or implicit, provided.   *)
+(*                                                                        *)
+(**************************************************************************)
+
+(* Hash Consed Patricia Trees *)
+
+module type Value = sig
+  type t
+  val equal : t -> t -> bool
+  val hash : t -> int
+end
+
+module type Bits = sig
+  type t
+
+  val lnot : t -> t
+  val (land) : t -> t -> t
+  val (lxor) : t -> t -> t
+  val (lor) : t -> t -> t
+  val (lsr) : t -> int -> t
+  val (lsl) : t -> int -> t
+  val pred : t -> t
+
+  val less_than : t -> t -> bool
+
+  val highest_bit : t -> t
+  val equal : t -> t -> bool
+  val hash : t -> int
+  val zero : t
+  val one : t
+
+  val size : int
+end
+
+module type Size = sig
+  val size : int
+end
+
+module Bits(S:Size) : sig
+  include Bits
+  val of_z : Z.t -> t
+  val to_z : t -> Z.t
+end
+
+module type S = sig
+  type key
+  type value
+  type mask
+  type t
+
+  val equal : t -> t -> bool
+
+  val empty : t
+  val singleton : key:key -> value:value -> mask:mask -> t
+
+  (** [add combine ~key ~value ?mask t]
+      Add a new key in the tree. If mask is specified, then we consider the whole
+      subtree stemming from key.
+
+      Assumes that forall x, [combine x x = x]
+  *)
+  val add : (value -> value -> value) -> key:key -> value:value ->
+    ?mask:mask -> t -> t
+
+  (** [remove key t] Remove the entire subtree speficied by the mask associated with
+      key in the tree. Otherwise remove only the key *)
+  val remove : key -> t -> t
+
+  (** [remove_exact key t] Remove the largest subtree
+      stemming from key. Otherwise remove only the key *)
+  val remove_exact : key -> t -> t
+
+  val remove_prefix : key -> mask -> t -> t
+
+  (** [mem key t] return true if the entire subtree speficied by the mask associated with
+      key is in the tree *)
+  val mem : key -> t -> bool
+
+  (** [mem_exact key t] return true if the largest subtree stemming from key is in the tree *)
+  val mem_exact : key -> t -> bool
+
+  val find : key -> t -> value option
+
+  (** [let new_tree = replace_subtree ~replaced value tree]
+      If replaced is a subtree of tree (for instance provided
+      by Map_reduce.reduce)
+      let n and m be the smallest integers such that for all
+      keys part of replaced, n is smaller and n + 2^m is strictly larger.
+      Then new_tree is the map such that for each key, n <= key < n + 2^m,
+      [find key new_tree] is [Some value] *)
+  val replace_subtree : replaced:t -> value -> t -> t
+
+  val fold : (key -> mask -> value -> 'a -> 'a) -> t -> 'a -> 'a
+
+  module type Map_Reduce = sig
+    type result
+    val default : result
+    val map : t -> key -> value -> result
+    val reduce : t -> result -> result -> result
+  end
+  module Map_Reduce(M:Map_Reduce) : sig
+    (** run has a constant amortized complexity *)
+    val run : t -> M.result
+
+    (** [filter f t] assumes that the composition of [f] and [reduce]
+        is monotonic i.e.
+        for any [t], if [f (reduce t x y) = true] then [f x = true]
+        and [f y = true].
+
+        For efficiency reason, you should also ensure that
+        if [f (reduce t x y) = false] then either [f x = false] or
+        [f y = false].
+        It is not required for correctness, but is needed to get a
+        constant amortized complexity.
+    *)
+    val filter : (M.result -> bool) -> t -> t
+  end
+
+end
+
+module Make_LE(V:Value) : S with type key = int and type value = V.t and type mask = int
+module Make_BE(V:Value) : S with type key = int and type value = V.t and type mask = int
+module Make_BE_gen(V:Value)(B:Bits) : S with type key = B.t and type value = V.t and type mask = B.t
+module Make_BE_sized(V:Value)(S:Size) : S with type key = Bits(S).t and type value = V.t and type mask = Bits(S).t
diff --git a/src/lib_stdlib/jbuild b/src/lib_stdlib/jbuild
index c32e851e0..dc15fb13d 100644
--- a/src/lib_stdlib/jbuild
+++ b/src/lib_stdlib/jbuild
@@ -7,6 +7,7 @@
               cstruct
               stringext
               hex
+              zarith
               lwt
               lwt.log))
   (flags (:standard -safe-string))))