Why do we put GMP allocations on GHC heaps?

[Florian Weimer]

* Simon Marlow:

> We did originally look at targetting the mpn API, but decided against
> it for the reasons alluded to above - the mpz layer has quite a lot of
> stuff in it that you would need to replicate.  For instance, when you
> start doing an operation some calculation has to be done to figure out
> how much memory to allocate for the result.

Sure, and you have to do sign handling.  The advantage is that you
could use a convenient encoding for length and sign, or deal with
carry/borrow in a flexible manner (i.e., stealing another word from
the allocation buffer).  It's not exactly trivial, but the effort may
be worth it.

> And be extra careful, because the GMP code is GPL, so our
> replacement for the mpz bits would probably end up being GPL too.

Actually, it's LGPL, and interesting bits are part of libc under an
even more permissive license.