Function efficiency of strtotime in php

 $start = array_sum(explode(' ', microtime()));
 for($i=0;$i<10000;++$i) {
 strtotime("- 1 day");
 }

 $end = array_sum(explode(' ', microtime()));

 echo $end - $start ;
 echo '';

 $start = array_sum(explode(' ', microtime()));

 for($i=0;$i<10000;++$i) {
 time() - 86400;
 }

 $end = array_sum(explode (' ', microtime()));

 echo $end - $start ;
?>

The output result is as follows: 1.13611793518 0.00332498550415

The efficiency difference is 400 times, which is indeed a big difference and deserves attention.