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The documentation for mt_rand() says that it produces numbers four times faster than the standard rand(). So, being that I use random numbers in my code often, I decided to test this.

Note: There is a followup to this article that discusses the randomness of the numbers generated by the two functions on different operating systems.

The test code:

<?php
	
$max = 100000;
	

	
$timeparts = explode(' ',microtime());
	
$stime = $timeparts[1].substr($timeparts[0],1);
	
$i = 0;
	
while($i < $max) {
	
rand();
	
$i++;
	
}
	
$timeparts = explode(' ',microtime());
	
$etime = $timeparts[1].substr($timeparts[0],1);
	
$time = $etime-$stime;
	
echo "{$max} random numbers generated in {$time} seconds using rand();<br/>";
	

	
$timeparts = explode(' ',microtime());
	
$stime = $timeparts[1].substr($timeparts[0],1);
	
$i = 0;
	
while($i < $max) {
	
mt_rand();
	
$i++;
	
}
	
$timeparts = explode(' ',microtime());
	
$etime = $timeparts[1].substr($timeparts[0],1);
	
$time = $etime-$stime;
	
echo "{$max} random numbers generated in {$time} seconds using mt_rand();<br/>";
	
?>
	

The Results:

On my laptop running a slightly outdated version of PHP 4.4 (around 4.4.0 if I remember correctly), the results were not as I expected. Most of the time, rand() was faster than mt_rand() by about 0.02 seconds. Of course, this isn't a big performance difference, but it's not the four times faster that was promised.

Sample:
100000 random numbers generated in 0.127249002457 seconds using rand();
100000 random numbers generated in 0.140385866165 seconds using mt_rand();

On TechnoServ, the results were closer. Usually rand() won by 0.01 seconds or less. Once again, not the supposed "four times faster."

Sample:
100000 random numbers generated in 0.11243796348572 seconds using rand();
100000 random numbers generated in 0.11861705780029 seconds using mt_rand();

So, despite the PHP documentation, rand() and mt_rand() are about the same speed, rand is just slightly faster.