<?php


$initial = 5;
$unit = 10;
$operation = '+';

function add($a, $b) { return $a + $b; }
function sub($a, $b) { return $a - $b; }

$operations = array('+' => 'add', '-' => 'sub');

$count = 100000;
$start = microtime(true);
for($i = 0; $i < $count; $i++)
    $operations[$operation]($initial, $unit);
$end = microtime(true);

echo "took " . number_format((($end - $start)/$count), 15) . " microseconds\n";

$start = microtime(true);
$str = "return $initial $operation $unit;";
for($i = 0; $i < $count; $i++)
    eval($str);
$end = microtime(true);

echo "took " . number_format((($end - $start)/$count), 15) . " microseconds\n";

?>