function getZipFilenames($archivo){
    $zip = new ZipArchive;
    $filenames = array();
    if($zip->open($archivo)){
        for($i=0; $i<$zip->numFiles; $i++){
            $zip_entry= $zip->statIndex($i);
            $name = $zip_entry['name'];
            $ext = getExtension($name);
            if(!isset($filenames[$ext])){
                $names = array();
                array_push($names, $name);
                $filenames[$ext] = $names;
            }
            else
                array_push($filenames[$ext], $name);
        }
    }
    return $filenames;
}