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: icatb_spm_existfile.m
    path of file: ./repos/bspm/thirdparty/MIALAB/GroupICATv4.0a/icatb/icatb_spm8_files
    
    the code of the file until where you have to start completion: function s = icatb_spm_existfile(filename)
% Check if a file exists on disk - a compiled routine

    
function s = icatb_spm_existfile(filename)
% Check if a file exists on disk - a compiled routine
% FORMAT S = SPM_EXISTFILE(FILENAME)
% FILENAME - filename (can also be a relative or full pathname to a file)
% S        - logical scalar, true if the file exists and false otherwise
%_______________________________________________________________________
%
% This compiled routine is equivalent to:
% >> s = exist(filename,'file') == 2;
% and was written for speed purposes. The differences in behaviour are:
%  * spm_existfile returns true for directory names
%  * spm_existfile does not look in MATLAB's search path
%  * spm_existfile returns false for an existing file that does not have
%    read permission
%_______________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging

% Guillaume Flandin
% $Id: spm_existfile.m 3100 2009-05-06 19:00:39Z guillaume $


%-This is merely the help file for the compiled routine
%error('spm_existfile.c not compiled - see Makefile')
persistent runonce
if isempty(runonce)
    warning('spm_existfile is not compiled for your platform.');
    runonce = 1;
end