FFI and Libraries using GMP
benjovi at gmx.net
Mon Sep 10 11:12:09 EDT 2007
I've been struggling using FFI bindings to libraries which rely on
the GNU Mp Bignum library (gmp) - this is apparently a well known
I do want to use some of those libraries however and so I started to
get them work on ghc-6.6.1/darwin_8_i368.
But as no solution was close to being satisfactory, I'd like to ask
for some advice.
Those two options worked to some extend:
Create or modify the library in question, so gmp is statically linked
and its symbols are hidden.
When source code is available, this is relatively easy, altough it
requires modification of the build process (which can be a hassle).
If a static "ar" archive is available, it is cumbersome (at least on
Mac Os X I ran into a lot of troubles using nmedit), but possible.
Furthermore, the resulting libraries are bloated, as each of them
contains a copy of the GMP; left alone portability issues.
As suggested in ticket#311, I tried switching the allocator functions
when switching to FFI. It worked, but not in GHCi; also, doing it
manually is a lot of work, because, as far as I could figure out, it
is neccessary to write a wrapper function for every C-function
(indirectly) using the gmp.
Furthermore, most of the libraries expose gmp datatypes (mpz_t,mpq_t)
in their API. I currently use a little haskell module working on
GHC.Exts, but that's propably not a good option from a maintainer's
point of view. There are certainly other possibilities, but I
couldn't find one which is both maintainable and portable.
I would be very grateful for any advice, or some information on plans
for resolving ticket #311; I'm aware that there are long-term plans
for replacing gmp, but I'd prefer a seperate short-term solution for
the problems with the FFI. There are some great libraries (like the
Parma Polyhedral Library, to pick an example) out there using gmp,
and it would be nice if writing bindings to those libs could be
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