use integer;
[...]
sub trivial_loop {
    my $from = shift;
    my $to;
    my $i;
    my $count = length $from;

    for ($i = 0; $i < $count; $i++) { $to = substr $from, $i, 1 }
}

sub duff {
    my $from = shift;  # real life would use reference here, this is a demo
    my $to;            # dummy: simulate write to serial i/o port
    my $i = 0;

    my ($n, $count);
    $count = length $from;

    $n = ($count + 7) / 8; # use integer in effect

    goto l. ($count % 8);           # number-only labels don't work :-(
    l0: do {    $to = (substr $from, $i++, 1);
    l7:         $to = (substr $from, $i++, 1);
    l6:         $to = (substr $from, $i++, 1);
    l5:         $to = (substr $from, $i++, 1);
    l4:         $to = (substr $from, $i++, 1);
    l3:         $to = (substr $from, $i++, 1);
    l2:         $to = (substr $from, $i++, 1);
    l1:         $to = (substr $from, $i++, 1);
        } while (--$n>0);
}