Validate IBAN number

This method will validate the format of IBAN number.

/**
* Check if the given parameter has valid IBAN.
* @author Samui Banti - https://samiwell.eu
* @param string $iban - The IBAN number.
* @return boolean - TRUE if the IBAN is valid.
*/
function checkIBAN($iban)
{
    $iban = strtolower(str_replace(' ','',$iban));
    
    $chars =  ['a'=>10,'b'=>11,'c'=>12,'d'=>13,'e'=>14,'f'=>15,'g'=>16,'h'=>17,'i'=>18,'j'=>19,'k'=>20,'l'=>21,'m'=>22,'n'=>23,'o'=>24,'p'=>25,'q'=>26,'r'=>27,'s'=>28,'t'=>29,'u'=>30,'v'=>31,'w'=>32,'x'=>33,'y'=>34,'z'=>35];
    
    $countries = [
    'al'=>28,'ad'=>24,'at'=>20,'az'=>28,'bh'=>22,'be'=>16,'ba'=>20,'br'=>29,'bg'=>22,'cr'=>21,'hr'=>21,'cy'=>28,'cz'=>24,'dk'=>18,'do'=>28,'ee'=>20,'fo'=>18,'fi'=>18,'fr'=>27,'ge'=>22,'de'=>22,'gi'=>23,'gr'=>27,'gl'=>18,'gt'=>28,'hu'=>28,'is'=>26,'ie'=>22,'il'=>23,'it'=>27,'jo'=>30,'kz'=>20,'kw'=>30,'lv'=>21,'lb'=>28,'li'=>21,'lt'=>20,'lu'=>20,'mk'=>19,'mt'=>31,'mr'=>27,'mu'=>30,'mc'=>27,'md'=>24,'me'=>22,'nl'=>18,'no'=>15,'pk'=>24,'ps'=>29,'pl'=>28,'pt'=>25,'qa'=>29,'ro'=>24,'sm'=>27,'sa'=>24,'rs'=>22,'sk'=>24,'si'=>19,'es'=>24,'se'=>24,'ch'=>21,'tn'=>24,'tr'=>26,'ae'=>23,'gb'=>22,'vg'=>24];

    if ( strlen($iban) == $countries[substr($iban,0,2)] ) {

        $movedChar = substr($iban, 4).substr($iban,0,4);
        $movedCharArray = str_split($movedChar);
        $newString = "";

        foreach ( $movedCharArray AS $key => $value ) {
            if( !is_numeric($movedCharArray[$key]) ) {
                $movedCharArray[$key] = $chars[$movedCharArray[$key]];
            }
            $newString .= $movedCharArray[$key];
        }

        if ( bcmod($newString, '97') == 1 ) {
            return true;
        } else {
            return false;
        }
    }
    
    return false;
}