<?php

$flip = array('even' => 'odd', 'odd' => 'even');
$class = 'even';

$time_start = microtime(true);
for ($number = 0; $number < 100000; $number++) {
  $class = ($number % 2 == 1) ? 'even': 'odd';
}
$time_end = microtime(true);
$old_time = $time_end - $time_start;

$time_start = microtime(true);
for ($number = 0; $number < 100000; $number++) {
  $class = $flip[$class];
}
$time_end = microtime(true);
$new_time = $time_end - $time_start;

echo "Old time is $old_time seconds\n";
echo "New time is $new_time seconds\n";
?>

// Result
Old time is -0.272475 seconds
New time is -0.420923 seconds