quick question about password hashing cost

[cloudll]

Hey guys, this is probably a silly question but just wanted to check.

 

This is from the PHP manual for password_needs_rehash

    if (password_needs_rehash($hash, PASSWORD_DEFAULT, $options)) {
        
        $newHash = password_hash($password, PASSWORD_DEFAULT, $options);

$options being the cost. I understand why the cost is being used for $newhash, but why is it being used for:

  if (password_needs_rehash($hash, PASSWORD_DEFAULT, $options)) {

Is that actually doing anything?

[QuickOldCar]

It's pretty much the purpose for that function, to compare if the options are the same for the hash.

 

Depends what is in the options, it could be a different cost or algorithm.

 

The reason it's there in the example is if you did change any options and to compare it the same.