	if ($CACHE) {
	    my $prog = read_file($tmpfn);
	    my $len = -s $tmpfn;
	    $cache{$len}{$prog} = $delta_result;
	    if ($len < $old_len) {
		foreach my $k (keys %cache) {
		    if ($k > ($len + $CACHE_PRUNE_SIZE)) {
			$cache{$k} = ();
		    }
		}
	    }
	    $old_len = $len;
	
}
