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$filter = [
   "LOGIC" => "OR",
   [
      "PERSONAL_BIRTHDAY_DATE" => $day->toString(new \Bitrix\Main\Context\Culture(array("FORMAT_DATETIME" => "m-d"))),
   ],
   [
      "DATE_REGISTER" => $day->toString(new \Bitrix\Main\Context\Culture(array("FORMAT_DATETIME" => "-m-d"))),
   ]

];

$dbUsers = CUser::getList(
    $by = 'CURRENT_BIRTHDAY', $order = 'ASC',
    $arFilter,
    array(
        'SELECT'     => $arRequiredFields,
        'NAV_PARAMS' => $arNavParams,
        'FIELDS'     => $arRequiredFields
    )
);

if($field == "CURRENT_BIRTHDAY")
{
    $cur_year = intval(date('Y'));
    $arSqlOrder[$field] = "IF(ISNULL(U.PERSONAL_BIRTHDAY), '9999-99-99', IF (
        DATE_FORMAT(U.PERSONAL_BIRTHDAY, '".$cur_year."-%m-%d') < DATE_FORMAT(DATE_ADD(".$DB->CurrentTimeFunction().", INTERVAL ".CTimeZone::GetOffset()." SECOND), '%Y-%m-%d'),
        DATE_FORMAT(U.PERSONAL_BIRTHDAY, '".($cur_year + 1)."-%m-%d'),
        DATE_FORMAT(U.PERSONAL_BIRTHDAY, '".$cur_year."-%m-%d')
    )) ".$dir;
}