EMS快递单号生成算法

<?php

function emsnum($ems, $num) {
    $fri = substr($ems, 2, 8);
    $head = substr($ems, 0, 2);
    $tail = substr($ems, -2);
    for ($i = 1; $i <= $num; $i++) {
        $num3 = substr($fri, 0, 1);
        $num4 = substr($fri, 1, 1);
        $num5 = substr($fri, 2, 1);
        $num6 = substr($fri, 3, 1);
        $num7 = substr($fri, 4, 1);
        $num8 = substr($fri, 5, 1);
        $num9 = substr($fri, 6, 1);
        $num0 = substr($fri, 7, 1);
        $mid = 8 * $num3 + 6 * $num4 + 4 * $num5 + 2 * $num6 + 3 * $num7 + 5 * $num8 + 9 * $num9 + 7 * $num0;
        $res = 11 - ($mid % 11);
        if ($res == 10) {
            $res = 0;
        }
        if ($res == 11) {
            $res = 5;
        }
        $emsres[$i] = $head . $fri . $res . $tail;
        $fri+= 1;
        $len = strlen($fri);
        if ($len < 8) {
            for ($j = $len; $j < 8; $j++) {
                $fri = "0" . $fri;
            }
        }
    }
    return $emsres;
}
$arr = emsnum("1014662951580", "20");
echo "<pre>";
var_dump($arr);
die;
?>