tin4=> sub {
  my $b = 0;
  $output[$_] = $arr[$b++] + $arr[$b++] + $arr[$b++]
    for 0..@arr/3;
},
tin5=> sub {
  my $b = -1;
  $output[$_] = $arr[++$b] + $arr[++$b] + $arr[++$b]
    for 0..@arr/3;
},