Multdiv64 only takes unsigned ints, and while I'm not familiar with the details of how that propagates to the division, it seems to result in nonsensical values for negative inputs.

Before copying this logic here I looked for an equivalent for signed ints but did not find any suitable one, and the expansion seemed simple enough.

You can see more details in https://github.com/openbmc/qemu/issues/14#issuecomment-437692215.