php 生成AlphaID

 0) {
                    $out -= pow($base, $pad_up);
                }
            }
            $out = sprintf('%F', $out);
            $out = substr($out, 0, strpos($out, '.'));
        } else {
            // Digital number  -->>  alphabet letter code
            if (is_numeric($pad_up)) {
                $pad_up--;
                if ($pad_up > 0) {
                    $in += pow($base, $pad_up);
                }
            }

            $out = "";
            for ($t = floor(log($in, $base)); $t >= 0; $t--) {
                $bcp = bcpow($base, $t);
                $a = floor($in / $bcp) % $base;
                $out = $out . substr($index, $a, 1);
                $in = $in - ($a * $bcp);
            }
            $out = strrev($out); // reverse
        }

        return $out;
    }

?>