count.php

<?php


function benchmark(callable $block) {

    $array = array();
    for ($i = 0; $i < 10000; $i++) {
        $array[] = mt_rand(1,1000000);
    }

    $start = microtime(true);
    $block($array);
    $end = microtime(true);
    return $end - $start;
}

echo 'Count each time：' . benchmark(function($array) {
    $try = 1000;
    $j = 0;
    while ($j < $try) {
        for ($i = 1; $i < count($array); ++$i){}
        $j++;
    }

}) . PHP_EOL;

echo 'Count in variable：' . benchmark(function($array) {
    $try = 1000;
    $j = 0;
    while ($j < $try) {
        $count = count($array);
        for ($i = 1; $i < $count; $i++){}
        $j++;
    }
}) . PHP_EOL;

PHP 5.4 on Debian 6.0 64bits.

% php count.php
Count each time：1.4978311061859
Count in variable：0.41650009155273