テストコードの効率

begin($start);
レポート($start);

function begin(&$start) {
 $tmp = gettimeofday();
 $start = $tmp[usec];
}

function report($start) {
 $tmp = gettimeofday();
 $now = $tmp[usec];
 echo "時間がかかる: ";
 echo $now - $start;
 echo "";
}

function getRandNum($length = 8) ) {
 $salt = substr(uniqid(rand()), -$length);
 return $salt;
}

$start = 0;
begin($start);
$str="";
while (strlen($str){
 $str.=getRandNum(1);
}
report($start);