How to gmp_import or gmp_export a negative value?

Greetings, All. I'm working with some big numbers my platform can't handle, and I need a way to store and retrieve them reliably. But much to my dismay, I've found that GMP is unable to handle negative numbers import/export. This can be demonstrated with a very short script: https://3v4l.org/gOENE <?php $x = "\xff"; $s = gmp_export(unpack('c', $x)[1], 1); printf("In: %d, Out: %d\n", ord($x), ord($s)); If this an intended behavior? Or am I missing some flag to make it work the desired way? -- Sincerely Yours, Andrey Repin <anrdaemon@freemail.ru>