MD5 Regex vs No regex

<?php

$isValidMd5Regex = function($md5=''){
  return preg_match('/^[a-f0-9]{32}$/', $md5);
};

$isValidMd5NoRegex = function ($md5=''){
  return strlen($md5) == 32 && ctype_xdigit($md5);
};

$list=[];

for($i=0;$i<10000;$i++){
  $j=32;
  if($i%2 == 0) $j=rand(1,128);
  $s='';
  for($k=0;$k<$j;$k++){
    if($j==32){
      $s.=chr(rand(0x61,0x7a));
    } else {
      $s.=chr(rand(0x21,0x7e));
    }
  }
  array_push($list,$s);
}

function check($func){
  global $list;
  $c = count($list);
  $start = microtime(true);
  for($i=0;$i<10000;$i++){
    for($j=0;$j<$c;$j++){
      $func($list[$j]);
    }
  }
  $end = microtime(true);
  $time = $end - $start;

  echo "Completed in $time\n";
}

check($isValidMd5Regex);
check($isValidMd5NoRegex);

?>

Completed in 8.948627948761
Completed in 5.0699028968811