Base10 到 Base64 网址缩短

我正在为一个正在学习 php 的项目编写一个 url 缩短函数，这是代码（顺便说一句，我想global这不是一件好事:P):

$alphabet = array(1 => "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",
                "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",
                "0","1","2","3","4","5","6","7","8","9","_","-");

function shorten($id){
    global $alphabet;
    $shortenedId = "";
    while($id>0){
        $remainder = $id % 64;
        $id = $id / 64;     
        $shortenedId = $alphabet[$remainder].$shortenedId;
    }
    return $shortenedId;
}

代码取自这篇维基百科文章并适配php。我的问题是，当我将 64 的倍数传递给函数时，我得到错误的（出于我的目的）结果，例如 128 返回 b，这是不正确的，它应该是 aaa，但这对于 3 位数字来说太长了数字。

另外，如果我将 1'000'000'000'000 传递为$id我得到 nItOq...我觉得这是错误的，因为像 bit.ly 这样的 url 缩短服务如果我使用它会返回一个 6 数字 id，而且我不认为这个算法比他们的更好。

那么，两个问题：

• 你发现上面的代码有什么错误吗？
• 如何管理64位多个ID？我是否必须忽略它们并转到下一个？

只需要一些小调整，主要的两个是使字母表零索引而不是一索引，并在除法之前从 id 中减去余数

function shorten($id)
{
    $alphabet = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_-';
    $shortenedId = '';
    while($id>0) {
        $remainder = $id % 64;
        $id = ($id-$remainder) / 64;     
        $shortenedId = $alphabet{$remainder} . $shortenedId;
    };
    return $shortenedId;
}

这是一个进一步修改的版本...我只是喜欢

function shorten($id, $alphabet='0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-')
{
    $base = strlen($alphabet);
    $short = '';
    while($id) {
        $id = ($id-($r=$id%$base))/$base;     
        $short = $alphabet{$r} . $short;
    };
    return $short;
}

EDIT:排序串联与 OP 相同