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function case_transform($str, $direction) // u2l, l2u
{
        $str1 = "0,1,2,3,4,5,6,7,8,9,а,б,в,г,д,е,ё,ж,з,и,й,к,л,м,н,о,п,р,с,т,у,ф,х,ц,ч,ш,щ,ъ,ы,ь,э,ю,я,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z";
	$str2 = "0,1,2,3,4,5,6,7,8,9,А,Б,В,Г,Д,Е,Ё,Ж,З,И,Й,К,Л,М,Н,О,П,Р,С,Т,У,Ф,Х,Ц,Ч,Ш,Щ,Ъ,Ы,Ь,Э,Ю,Я,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z";

    $src = $direction == "u2l" ? preg_split("/,/", $str2) : preg_split("/,/", $str1);
    $dst = $direction == "u2l" ? preg_split("/,/", $str1) : preg_split("/,/", $str2);

    $res = "";
    for ($i = 0; $i < strlen($str); $i++) {
        $tv = array_search(substr($str, $i, 1), $src);
        if ($tv) {
            $res .= $dst[$tv];
        } else {
            $res .= substr($str, $i, 1);
        }
    }
    return $res;
}

function low2up($str)
{
    return case_transform($str, "l2u");
}

function up2low($str)
{
    return case_transform($str, "u2l");
}