You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: read_trigger.m
    path of file: ./repos/bspm/thirdparty/spm12/external/fieldtrip/fileio/private
    
    the code of the file until where you have to start completion: function [event] = read_trigger(filename, varargin)

% READ_TRIGGER extracts the events from a continuous trigger channel
% This function is a helper function to read_event and can be used for all
% dataformats that have one or multiple continuously sampled TTL channels
% in the data.
%
% This is a helper function for FT_READ_EVENT. Please look at the code of
% this function for further details.
%
% TODO
%  - merge read_ctf_trigger into this function (requires trigshift and bitmasking option)
%  - merge biosemi code into this function (requires bitmasking option)

% Copyright (C) 2008-2015, Robert Oostenveld
%
% This file is part of FieldTrip, see http://www.fieldtriptoolbox.org
% for the documentation and details.
%
%    FieldTrip 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 3 of the License, or
%    (at your option) any later version.
%
%    FieldTrip 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

    
function [event] = read_trigger(filename, varargin)

% READ_TRIGGER extracts the events from a continuous trigger channel
% This function is a helper function to read_event and can be used for all
% dataformats that have one or multiple continuously sampled TTL channels
% in the data.
%
% This is a helper function for FT_READ_EVENT. Please look at the code of
% this function for further details.
%
% TODO
%  - merge read_ctf_trigger into this function (requires trigshift and bitmasking option)
%  - merge biosemi code into this function (requires bitmasking option)

% Copyright (C) 2008-2015, Robert Oostenveld
%
% This file is part of FieldTrip, see http://www.fieldtriptoolbox.org
% for the documentation and details.
%
%    FieldTrip 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 3 of the License, or
%    (at your option) any later version.
%
%    FieldTrip 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 FieldTrip. If not, see <http://www.gnu.org/licenses/>.
%
% $Id$

% get the optional input arguments
hdr          = ft_getopt(varargin, 'header'             );
dataformat   = ft_getopt(varargin, 'dataformat'         );
begsample    = ft_getopt(varargin, 'begsample'          );
end