For decompressing, i modified a function posted earlier (that way $string doesn't have a big size that may be beyond the memory limit if the gzipped file is big) :

function file_ungzip($fromFile, $toFile) {
    $zp = @gzopen($fromFile, "r");
    $fp = @fopen($toFile, "w");
    while(!@gzeof($zp)) {$string = @gzread($zp, 4096); @fwrite($fp, $string, strlen($string));}
    @gzclose($zp);
    @fclose($fp);
}