php 求质素（素数） 的实现代码

<?php 
class timer 
{ 
var $time_start; 
var $time_end; function __construct() 
{ 
$this->time_start = 0; 
$this->time_end = 0; 
} 
function timer() 
{ 
$this->__construct(); 
} 
function start() 
{ 
list($usec,$sec) = explode(" ",microtime()); 
$this->time_start = (float)$usec + (float)$sec; 
} 
function stop() 
{ 
list($usec,$sec) = explode(" ",microtime()); 
$this->time_end = (float)$usec + (float)$sec; 
} 
function show($output = false) 
{ 
$total = $this->time_end - $this->time_start; 
if ($output) { 
echo $total," sec"; 
return true; 
} 
return $total." sec"; 
} 
} 
?> 
<?php 
echo 'check prime<br/>'; 
function IsPrime($i) 
{ 
if($i<2) 
{ 
return false; 
} 
//var $iterator; 
for($iterator = 2 ; $iterator <= sqrt($i) ; $iterator++) 
{ 
if($i % $iterator==0) 
{ 
return false; 
} 
} 
return true; 
} 
$sw=new timer(); 
$sw->start(); 
for($j=1;$j<100;$j++) 
{ 
if(IsPrime($j)) 
{ 
echo 'true<br/>'; 
} 
else 
{ 
echo 'false<br/>'; 
} 
} 
$sw->stop(); 
$sw->show(true); 
?>