Your benchmark still has a flaw; it's using the same variable to increment. So one case is incrementing from 0, the other from where the first one left off. It may not make a difference, but how can you be sure.

Of course, the biggest flaw is the use the Benchmark module itself. How can use trust a module that sometimes reports negative times? 

#!/usr/bin/perl

use strict;
use warnings;
use Time::HiRes 'gettimeofday';

my $ITERATIONS = 10_000_000;

my $counter1  = 0;
my $counter2  = 0;

my ($s1, $m1) = gettimeofday;
for (1 .. $ITERATIONS) {$a = ++$counter1 & 1}
my ($s2, $m2) = gettimeofday;
for (1 .. $ITERATIONS) {$a = ++$counter2 % 2}
my ($s3, $m3) = gettimeofday;

my $d1 = $s2 - $s1 + ($m2 - $m1) / 1_000_000;
my $d2 = $s3 - $s2 + ($m3 - $m2) / 1_000_000;

printf "And: %.6f  Mod: %.6f\n", $d1, $d2;

__END__
And: 2.954181  Mod: 3.093696
And: 3.320696  Mod: 3.321606
And: 3.096083  Mod: 3.218991
And: 2.977993  Mod: 3.113543
And: 2.954634  Mod: 3.100933
And: 2.836724  Mod: 3.168724
And: 2.880770  Mod: 3.472917
And: 3.117684  Mod: 3.552177
And: 3.668317  Mod: 3.616199
And: 3.126708  Mod: 3.126385

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In reply to Re^2: &1 is no faster than %2 when checking for oddness. (Careful what you benchmark) by Anonymous Monk
in thread &1 is no faster than %2 when checking for oddness. Oh well. by diotalevi

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