Php 反向算法

我使用此算法将MongoID压缩到20个字符，从这里开始：。 但是，我很难将其反转并检索回我的24个字符

有人能给我一些指导吗

我使用的代码：

$padded = str_repeat('0', 20 - strlen($purchase_id)) . $purchase_id;
$leastSignificant = base_convert(substr($padded, 14, 10), 32, 16); // will be 8 chars most

$middleSignificant = base_convert(substr($padded, 4, 10), 32, 16); // will be 8 chars most

$highSignificant = base_convert(substr($padded, 0, 4), 32, 16); // will be 4 chars most

// Concatenate, and make sure everything is correctly padded
$result = str_repeat('0', 4 - strlen($highSignificant)) . $highSignificant .
          str_repeat('0', 8 - strlen($middleSignificant )) . $middleSignificant .
          str_repeat('0', 8 - strlen($leastSignificant )) . $leastSignificant;

我收到错误：

警告：str_repeat（）：第二个参数必须大于或等于0

我得到了与我的原始MongoID相对应的最小重要值和高重要值。但这并不重要。我得到了25个字符而不是24个。

得到了

// Pad with 0's to make sure you have 20 chars
$padded = str_repeat('0', 20 - strlen($purchase_id)) . $purchase_id;

$leastSignificant = base_convert(substr($padded, 12, 8), 32, 16); // will be 10 chars most
    var_dumped($leastSignificant,false);

$middleSignificant = base_convert(substr($padded, 4, 8), 32, 16); // will be 10 chars most
    var_dumped($middleSignificant,false);

$highSignificant = base_convert(substr($padded, 0, 4), 32, 16); // will be 4 chars most
    var_dumped($highSignificant,false);

// Concatenate, and make sure everything is correctly padded
$result = str_repeat('0', 4 - strlen($highSignificant)) . $highSignificant .
          str_repeat('0', 10 - strlen($middleSignificant )) . $middleSignificant .
          str_repeat('0', 10 - strlen($leastSignificant )) . $leastSignificant;