Liam Healy - CFFI-FSBV first light
Sep. 25th, 2011
11:33 pm - CFFI-FSBV first light
Luis and I have been working on merging FSBV into CFFI as a new system CFFI-FSBV. This will allow calling foreign functions with structures passed and/or returned by value. It uses libffi.
The new system will have some advantages over the old. From the users perspective, there won't be a need to download a separate repository, and there won't be a need to directly use anything from CFFI-FSBV; all calls by value look just like regular CFFI with the appropriate type declarations. Based on a discussion on the cffi-devel mailing list, we decided and Luis implemented the syntax (:struct foo) for the structure (by value) and (:pointer (:struct foo)) for the pointer. Using 'foo directly is accepted for now with a warning, but is deprecated.
We now have, as astronomers say about a new telescope, "first light". Using my favorite complex number example from GSL
(defcstruct (complex-double :class complex-type) (dat :double :count 2))
and then with a few more definitions, we can call the foreign functions with the structure passed by value,
(foreign-funcall "gsl_complex_conjugate" (:struct complex-double) #C(3.0d0 4.0d0) (:struct complex-double)) #C(3.0d0 -4.0d0) (foreign-funcall "gsl_complex_abs" (:struct complex-double) #C(3.0d0 4.0d0) :double) 5.0d0
Soon I hope we can reduce the "few more definitions", which do the translation between Lisp and C and are given in fsbv/examples.lisp, to something like what's in the old system's definition of defcstruct, with :constructor and :deconstructor options.
There's a lot more to do before this is ready for release, but we've got a start. The work is in the fsbv branch.