$results = timethese(1000000,{
tin1 => '$output[int($_/3)] += $arr[$_] for 0..@arr-1;',
tin2 =>'$out[$_] = ($arr[(3*$_)]+$arr[(3*$_+1)]+$arr[(3*$_+2)]) for 0..(scalar(@arr)/3 - 1);',
tin3=>'for (0..$k) {
    $output[$_] = $arr[$b] + $arr[$b+1] + $arr[$b +2];
    $b += 3;
}
'});
Benchmark::cmpthese( $results );