Empty Loop Micro-benchmarks. Useless except for curiosity.

loops.php

<?php

define('ITERATIONS', 10000000);
$var = 0;

$start = microtime(true);
$var = 0;
while ($var < ITERATIONS) {
  ++$var;
}
$stop = microtime(true);
printf("Loop type %8s took %f seconds\n", 'while', $stop - $start);

$start = microtime(true);
$var = 0;
do {
  ++$var;
} while ($var < ITERATIONS);
$stop = microtime(true);
printf("Loop type %8s took %f seconds\n", 'do-while', $stop - $start);

$start = microtime(true);
for ($var = 0; $var < ITERATIONS; ++$var) {
  //do nothing
}
$stop = microtime(true);
printf("Loop type %8s took %f seconds\n", 'for', $stop - $start);

Results: http://3v4l.org/FdPvW