function getZipFilenames($archivo){
    $zip = zip_open($archivo);
    $filenames = array();
    if($zip){
        while($zip_entry = zip_read($zip)){
            $name = zip_entry_name($zip_entry);
            $ext = getExtension($name);
            if(!isset($filenames[$ext])){
                $names = array();
                array_push($names, $name);
                $filenames[$ext] = $names;
            }
            else
                array_push($filenames[$ext], $name);
        }
    }
    return $filenames;
}