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# Source code for PIL.DcxImagePlugin

    #
    # The Python Imaging Library.
    # $Id$
    #
    # DCX file handling
    #
    # DCX is a container file format defined by Intel, commonly used
    # for fax applications.  Each DCX file consists of a directory
    # (a list of file offsets) followed by a set of (usually 1-bit)
    # PCX files.
    #
    # History:
    # 1995-09-09 fl   Created
    # 1996-03-20 fl   Properly derived from PcxImageFile.
    # 1998-07-15 fl   Renamed offset attribute to avoid name clash
    # 2002-07-30 fl   Fixed file handling
    #
    # Copyright (c) 1997-98 by Secret Labs AB.
    # Copyright (c) 1995-96 by Fredrik Lundh.
    #
    # See the README file for information on usage and redistribution.
    #
    from __future__ import annotations

    from . import Image
    from ._binary import i32le as i32
    from ._util import DeferredError
    from .PcxImagePlugin import PcxImageFile

    MAGIC = 0x3ADE68B1  # QUIZ: what's this value, then?

    def _accept(prefix: bytes) -> bool:
        return len(prefix) >= 4 and i32(prefix) == MAGIC

    ##
    # Image plugin for the Intel DCX format.

    class DcxImageFile(PcxImageFile):
        format = "DCX"
        format_description = "Intel DCX"
        _close_exclusive_fp_after_loading = False

        def _open(self) -> None:
            # Header
            assert self.fp is not None
            s = self.fp.read(4)
            if not _accept(s):
                msg = "not a DCX file"
                raise SyntaxError(msg)

            # Component directory
            self._offset = []
            for i in range(1024):
                offset = i32(self.fp.read(4))
                if not offset:
                    break
                self._offset.append(offset)

            self._fp = self.fp
            self.frame = -1
            self.n_frames = len(self._offset)
            self.is_animated = self.n_frames > 1
            self.seek(0)

        def seek(self, frame: int) -> None:
            if not self._seek_check(frame):
                return
            if isinstance(self._fp, DeferredError):
                raise self._fp.ex
            self.frame = frame
            self.fp = self._fp
            self.fp.seek(self._offset[frame])
            PcxImageFile._open(self)

        def tell(self) -> int:
            return self.frame

    Image.register_open(DcxImageFile.format, DcxImageFile, _accept)

    Image.register_extension(DcxImageFile.format, ".dcx")