FFI Bindings to Libraries using GMP

benedikth benjovi at gmx.net
Mon Sep 10 09:39:53 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 problem
I do rely on using such libraries, and so started to get it work on 
MacOsX; no solution was close to being satisfactory however, so 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. 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 simplified.

Benedikt Huber

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