php中英文字符串转字母转大小写

<?php
    //转小写
    function lowercase($a){  
        $b = str_split($a, 1);  
        $r = '';
        foreach($b as $v){  
            $v = ord($v);  
            if($v >= 65 && $v<= 90){  
                $v += 32;  
            }  
            $r .= chr($v);  
        }  
        return $r;  
    }
    //转大写
    function capital($a){  
        $b = str_split($a, 1);  
        $r = '';  
        foreach($b as $v){  
            $v = ord($v);  
            if($v >= 97 && $v<= 122){  
                $v -= 32;  
            }  
            $r .= chr($v);  
        }  
        return $r;  
    }  
?>