sub sortQ3{
    local our @dst;
    ( my( $s, $e ), *dst ) = @_;
    my $t;
    my $m = $s-1;
    $dst[ $_ ] < $dst[ $e ]
        and $t = $dst[++$m], $dst[$m] = $dst[$_], $dst[$_] = $t
        for $s .. $e;

    $t = $dst[++$m], $dst[$m] = $dst[$e], $dst[$e] = $t;

    sortQ3( $s, $m-1, \@dst ) if $s  < $m-1;
    sortQ3( $m+1, $e, \@dst ) if $m+1< $e;
}