code.php

<?php
class Code{
    private $dic = array(
        0=>'0', 1=>'1', 2=>'2', 3=>'3', 4=>'4', 5=>'5', 6=>'6', 7=>'7', 8=>'8',
        9=>'9', 10=>'A',  11=>'B', 12=>'C', 13=>'D', 14=>'E', 15=>'F',  16=>'G',  17=>'H',
        18=>'I',19=>'J',  20=>'K', 21=>'L',  22=>'M',  23=>'N', 24=>'O', 25=>'P', 26=>'Q',
        27=>'R',28=>'S',  29=>'T',  30=>'U', 31=>'V',  32=>'W',  33=>'X', 34=>'Y', 35=>'Z'
    );

    public function encodeID($int,$format=8){
        $dics = $this->dic;
        $dnum = 36;
        $arr = array();
        $loop = true;
        while($loop){
            $arr[] = $dics[bcmod($int,$dnum)];
            $int  = bcdiv($int,$dnum,0);
            if($int == '0'){
                $loop = false;
            }
        }
        if(count($arr) < $format){
            $arr = array_pad($arr,$format,$dics[0]);
        }
        return implode('',array_reverse($arr));
    }

    public function decodeID($ids){
        $dics  = $this->dic;
        $dnum = 36;
        $dedic = array_flip($dics);
        $id = ltrim($ids,$dics[0]);
        $id = strrev($id);
        $v = 0;
        for($i = 0, $j = strlen($id); $i < $j ; $i++){
            $v = bcadd(bcmul($dedic[$id {
                $i}
                ],bcpow($dnum,$i,0),0),$v,0);
        }
        return $v;
    }
}
$code = new Code();
$card_no = $code->encodeID(888888,5);
echo $card_no."<br/>";

echo $code->decodeID($card_no);