sub _r_max {
    my $h = shift;
    return $h unless @_;
    $_[0] = $h if $h > $_[0];
    &_r_max;
}
sub r_max{ _r_max( @{[ @_ ]} ) }

__END__
C:\test>junk3 -N=100
           Rate      amp unrolled    r_max
amp      4755/s       --     -35%     -50%
unrolled 7275/s      53%       --     -24%
r_max    9522/s     100%      31%       --

C:\test>junk3 -N=2000
          Rate      amp unrolled    r_max
amp      183/s       --     -50%     -51%
unrolled 363/s      98%       --      -2%
r_max    372/s     103%       2%       --