how to allow only gmail and yahoo user to register on my website how to ban other

function cust_restrict_mail_providers() {

    $authorized_providers = array(
        'gmail.com',
        'yahoo.com',
        'hotmail.com'
    );
    $current_provider = preg_replace('/^.*@(.*)$/i', '$1', Params::getParam('s_email'));

    if (!in_array($current_provider, $authorized_providers)) {
        osc_add_flash_error_message( _m('Your current email is not allowed'));
        osc_redirect_to(osc_register_account_url());
exit;
    }

where to add this code, please.

Bottom of function.php

@oneloveb
I needed that,
Thank you

@mocody
You're Welome