You're right. I never use gettimeofday, and mistakenly assumed it returned millseconds not microseconds.

Now, beside being wrong, you are also inconsistent. In your first point, you accuse me of not dividing by the number of iterations, as if the value wouldn't be a number of sub-second units. Then in your second point you do think it's a number of sub-second units. You can't have it both ways.

I misunderstood your arcane way of doing floating point math and thought you were dividing by the (wrong) number of iterations. I misundertsood your code, for which I apologise, but there is no inconsistancy. Good enough reason to use a module rather than hand code the math.

I also noted "Without having analysed it too closely, you appear to have a precedence problem in your delta calculations.".

That said, even if we return to using your arcane floating point math and bizarre failure to break down the results on a per iteration basis, the results of your benchmark method, modified by the removal of your $a fopar, still shows that & 1 is consistantly faster than % 2.

#! perl -slw
use strict;
use Time::HiRes 'gettimeofday';

our $ITERS ||= 10_000_000;

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

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

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

printf "And: %.9f  Mod: %.9f\n", $d1, $d2;

__END__
c:\test>junk2 -ITERS=1e6
And: 0.258308000  Mod: 0.304192000

c:\test>junk2 -ITERS=1e6
And: 0.258755000  Mod: 0.272495000

c:\test>junk2 -ITERS=1e6
And: 0.259628000  Mod: 0.302872000

c:\test>junk2 -ITERS=10e6
And: 2.656250000  Mod: 2.828125000

c:\test>junk2 -ITERS=10e6
And: 2.671875000  Mod: 2.859375000

c:\test>junk2 -ITERS=10e6
And: 2.671875000  Mod: 2.859375000

c:\test>junk2 -ITERS=100e6
And: 26.187500000  Mod: 28.375000000

c:\test>junk2 -ITERS=100e6
And: 26.265625000  Mod: 28.328125000
[download]

And the more iterations you run (therebye reducing the obscuring affects of the invariant parts of the code under test), the more consistant it becomes.

Just as was shown by both my Benchmark method and lidden's external timer method.