How can I do this faster?

Question

this is my code:

$valid = true;
$len = strlen($packet->username);
if($len > 16 or $len < 3){
    $valid = false;
}
for($i = 0; $i < $len and $valid; ++$i){
    $c = ord($packet->username{$i});
    if(($c >= ord("a") and $c <= ord("z")) or
        ($c >= ord("A") and $c <= ord("Z")) or
        ($c >= ord("0") and $c <= ord("9")) or $c === ord("_") ){
        continue;
    }
    $valid = false;
    break;
}
if(!$valid or $this->iusername === "rcon" or $this->iusername === "console"){
    $this->close("", "§ePlease make sure your username is longer then §a3§e characters\n§eand only uses numbers and letters§7.");
    return;
}

It checks usernames to make sure it is valid. This code is too slow, and it loops $len times which causes seconds wasted doing nothing on my main thread. Anyone know any solutions to make this faster & possibly remove the loop?

Answer 1

use this:

$username = 'admin';

$valid = preg_match('/^[\w\d]{3,16}$/',$username);

if(!$valid){
    echo 'Bad character in your username !';
}

$invalidUsername = array(
    'admin',
    'root',
    'localhost'
);

if(in_array($username, $invalidUsername)) {
    echo "Username is not valid !";
}

return true;

Answer 2

Simple regex:

$valid = (preg_match('/[^A-Z0-9_]/i', $username) === 0);

Check for anything that ISN'T alphabetical/numerical/underscore. If nothing is found (0 matches), then the username is valid. Otherwise it's invalid.