(***********************************************************************)
(*                                                                     *)
(*                                OCaml                                *)
(*                                                                     *)
(*            Xavier Leroy, projet Cristal, INRIA Rocquencourt         *)
(*                                                                     *)
(*  Copyright 1996 Institut National de Recherche en Informatique et   *)
(*  en Automatique.  All rights reserved.  This file is distributed    *)
(*  under the terms of the GNU Library General Public License, with    *)
(*  the special exception on linking described in file ../LICENSE.     *)
(*                                                                     *)
(***********************************************************************)

(* Operations on internal representations of values *)

type t

external repr : 'a -> t = "%identity"
external obj : t -> 'a = "%identity"
external magic : 'a -> 'b = "%identity"
external is_block : t -> bool = "caml_obj_is_block"
external is_int : t -> bool = "%obj_is_int"
external tag : t -> int = "caml_obj_tag"
external set_tag : t -> int -> unit = "caml_obj_set_tag"
external size : t -> int = "%obj_size"
external field : t -> int -> t = "%obj_field"
external set_field : t -> int -> t -> unit = "%obj_set_field"
let double_field x i = Array.get (obj x : float array) i
let set_double_field x i v = Array.set (obj x : float array) i v
external new_block : int -> int -> t = "caml_obj_block"
external dup : t -> t = "caml_obj_dup"
external truncate : t -> int -> unit = "caml_obj_truncate"
external add_offset : t -> Int32.t -> t = "caml_obj_add_offset"

let marshal (obj : t) =
  Marshal.to_bytes obj []
let unmarshal str pos =
  (Marshal.from_bytes str pos, pos + Marshal.total_size str pos)

let lazy_tag = 246
let closure_tag = 247
let object_tag = 248
let infix_tag = 249
let forward_tag = 250

let no_scan_tag = 251

let abstract_tag = 251
let string_tag = 252
let double_tag = 253
let double_array_tag = 254
let custom_tag = 255
let final_tag = custom_tag


let int_tag = 1000
let out_of_heap_tag = 1001
let unaligned_tag = 1002

let extension_slot x =
  let x = repr x in
  let slot =
    if (is_block x) && (tag x) <> object_tag && (size x) >= 1 then field x 0
    else x
  in
  let name =
    if (is_block slot) && (tag slot) = object_tag then field slot 0
    else raise Not_found
  in
    if (tag name) = string_tag then slot
    else raise Not_found

let extension_name x =
  try
    let slot = extension_slot x in
      (obj (field slot 0) : string)
  with Not_found -> invalid_arg "Obj.extension_name"

let extension_id x =
  try
    let slot = extension_slot x in
      (obj (field slot 1) : int)
  with Not_found -> invalid_arg "Obj.extension_id"

let extension_slot x =
  try
    extension_slot x
  with Not_found -> invalid_arg "Obj.extension_slot"
