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(*
* Copyright 2003-2006 Savonet team
*
* This file is part of OCaml-mad.
*
* Ocaml-mad is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* Ocaml-mad 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. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Ocaml-mad; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*)
(**
* Decode message encoded using private bits.
*
* @author Romain Beauxis
*)
(* $Id$ *)
let src = ref ""
let usage = "usage: decode_msg source"
let last = ref (false, true, false)
let state () =
let x, _, _ = !last in
x
let started = ref false
let iob b = if b then 1 else 0
let get_bits mf char =
let frame = Mad.get_frame_format mf in
let cp = frame.Mad.copyright in
let oi = frame.Mad.original in
let pr = frame.Mad.private_bit in
let lcp, _, _ = !last in
last := (cp, oi, pr);
if cp = not lcp then begin
let char = (char lsl 1) + iob oi in
(true, (char lsl 1) + iob pr)
end
else (false, char)
let is_sync mf =
let frame = Mad.get_frame_format mf in
let cp = frame.Mad.copyright in
let oi = frame.Mad.original in
let pr = frame.Mad.private_bit in
let lcp, loi, lpr = !last in
last := (cp, oi, pr);
if !started && loi = not oi && lpr = not pr && cp = lcp then true
else begin
started := true;
false
end
let _ =
Arg.parse []
(let pnum = ref (-1) in
fun s ->
incr pnum;
match !pnum with
| 0 -> src := s
| _ ->
Printf.eprintf "Error: too many arguments\n";
exit 1)
usage;
if !src = "" then (
Printf.printf "%s\n" usage;
exit 1);
let synced = ref false in
let msg_char = ref 0 in
let bit_pos = ref 0 in
let mf = Mad.openfile !src in
(try
while true do
Mad.skip_frame mf;
begin
match !synced with
| false when is_sync mf -> synced := true
| false -> ()
| true ->
let incr, char = get_bits mf !msg_char in
msg_char := char;
if incr then bit_pos := !bit_pos + 2
end;
if !bit_pos > 7 then begin
Printf.printf "%C%!" (char_of_int !msg_char);
msg_char := 0;
bit_pos := 0;
synced := false
end
done;
assert false
with Mad.End_of_stream -> Mad.close mf);
Printf.printf "\n"
|
