如何映射（大）整数（大小）（用PHP的字母数字字符串？（Cantor？）

I can't figure out how to optimally do the following in PHP: In a database, I have messages with a unique ID, like 19041985. Now, I want to refer to these messages in a short-url service but not using generated hashes but by simply 'calculate' the original ID.I can't figure out how to optimally do the foll