> This isn't purely academic.  The `decimal` docs, at the end:

Yes, that is a good point. I think for libmpdec I'll just do a trial divmod if prec > BIGNUM_THRESHOLD.



> Perhaps the only thing to be done is to add words to the part of the docs _recommending_ MAX_PREC, warning about some "unintended consequences" of doing so.

This, too. Probably some formula based on the amount of available RAM would do.