clearly the massive differences between tin2 and tin3 must at least alert you that something is wrong with the benchmark... Frankly I have no idea what goes on once you start eval-ing strings in the Benchmark module, but from the presented examples, something seems suspicious.

Here is a benchmark by me 

use Benchmark qw(cmpthese);

my @arr = map {rand} 0..900000;
my @output = map {rand} 0..300000;;

Benchmark::cmpthese(10,{
tin1 => sub { 
  $output[int($_/3)] += $arr[$_] for 0..@arr-1; 
},
tin2 => sub {
  $output[$_] =  $arr[3*$_] + $arr[3*$_+1] + $arr[3*$_+2]
    for 0..@arr/3;
},
tin3=> sub {
  my $b = 0;
  for (0..@arr /3) {
    $output[$_] = $arr[$b] + $arr[$b+1] + $arr[$b +2];
    $b += 3;
  }
}
});

[download]
With result 
$ perl ../../../perlmonks/bench-trip.pl
       Rate tin1 tin2 tin3
tin1 1.81/s   -- -41% -46%
tin2 3.08/s  70%   --  -9%
tin3 3.39/s  87%  10%   --

[download]

In reply to Re^3: Summing Up Array Elements By Group by ivancho
in thread Summing Up Array Elements By Group by neversaint

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