PHP Duff's device
Duffs device is implimentation of loop unrolling. You can speed up the script execution by running the loop N/n times but run in the loop (unrolling) the same command multiple times.
<?php
$iterations = 16;
$val = 0;
$n = $iterations / 8;
while ($n--)
{
$val++;
$val++;
$val++;
$val++;
$val++;
$val++;
$val++;
$val++;
}