[cffi-devel] CFFI and GSL (spline function) help needed

[Heiko Schroeter]

Hello,

i want to use the GSL spline functionallity from within SBCL using the CFFI 
interface.
So far i can do the "simple" functions returning pointers and/or values like 
the BESSEL function for example.

Now i 'am trying to setup an interface for the spline function but cannot 
manage to handle the "gsl_interp_cpline" pointer in lisp correctly.
I did copy the needed parts here for simplicity:

/***************** gsl_types.h ************************/
<snip>
#    define GSL_VAR extern
<snap>
/***************** gsl_interp.h ***********************/
/* evaluation accelerator */
typedef struct {
  size_t  cache;        /* cache of index   */
  size_t  miss_count;   /* keep statistics  */
  size_t  hit_count;
}
gsl_interp_accel;

/* interpolation object type */
typedef struct {
  const char * name;
  unsigned int min_size;
  void *  (*alloc) (size_t size);
  int     (*init)    (void *, const double xa[], const double ya[], size_t 
size);
  int     (*eval)    (const void *, const double xa[], const double ya[], 
size_t size, double x, gsl_interp_accel *, double * y);
  int     (*eval_deriv)  (const void *, const double xa[], const double ya[], 
size_t size, double x, gsl_interp_accel *, double * y_p);
  int     (*eval_deriv2) (const void *, const double xa[], const double ya[], 
size_t size, double x, gsl_interp_accel *, double * y_pp);
  int     (*eval_integ)  (const void *, const double xa[], const double ya[], 
size_t size, gsl_interp_accel *, double a, double b, double * result);
  void    (*free)         (void *);

} gsl_interp_type;

/* general interpolation object */
typedef struct {
  const gsl_interp_type * type;
  double  xmin;
  double  xmax;
  size_t  size;
  void * state;
} gsl_interp;

/* available types */
GSL_VAR const gsl_interp_type * gsl_interp_cspline;

gsl_interp_accel *
gsl_interp_accel_alloc(void);

/********************** gsl_spline.h *********************************/
/* general interpolation object */

typedef struct {
  gsl_interp * interp;
  double  * x;
  double  * y;
  size_t  size;
} gsl_spline;

gsl_spline *
gsl_spline_alloc(const gsl_interp_type * T, size_t size);

/********************* example.c **************************************/
<snip>
    gsl_interp_accel *acc 
      = gsl_interp_accel_alloc ();
    gsl_spline *spline 
      = gsl_spline_alloc (gsl_interp_cspline, 10);
<snap>
/*********************************************************************/

My lisp translation so far:

(defpackage :cffi-user
   (:use :common-lisp :cffi))
(in-package :cffi-user)

(pushnew #P"/usr/local/lib/" *foreign-library-directories*
	 :test #'equal)

(define-foreign-library libgslcblas
  (:unix (:or "libgslcblas.so.0.0.0" "libgslcblas.so.0"))
  (t (:default "libgslcblas")))
(use-foreign-library libgslcblas)

(define-foreign-library libgsl
  (:unix (:or "libgsl.so.0.9.0" "libgsl.so.0"))
  (t (:default "libgsl")))
(use-foreign-library libgsl)

;;;; just to test the interface
(defcfun "gsl_sf_bessel_J0" :double (x :double))
(format t "~A~%" (gsl-sf-bessel-J0 5d0))
;;;; ok so far

(defcfun "gsl_interp_accel_alloc" :void)
(defparameter *gsl-int-acc-alloc* (gsl-interp-accel-alloc))
;;;; looks ok so far

(defctype gsl-cspline :pointer) <--- trouble

(defcfun "gsl_spline_alloc" :pointer
  (ptr :pointer)
  (n :int))
(defparameter *gsl-spline-alloc* (gsl-spline-alloc gsl-cspline 10))

My problem is that i cannot set this typed struc pointer "gsl_interp_cpline" 
correctly.
Memory allocation ?
What is the "magic" trick here ?

Heiko