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From: hreba <f_hreba@yahoo.com.br>
Newsgroups: comp.lang.ada
Subject: Interfaces.C + generics: stack overflow
Date: Thu, 23 Mar 2017 08:43:10 +0100
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Date: 2017-03-23T08:43:10+01:00
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My last posting was buried deep inside the thread and somewhat lengthy, 
so here in a compact form. What works is (everything compiles and test 
application executes):

--------------------------------------------------------------------
with Interfaces;

package GSL is
    subtype Real is Interfaces.IEEE_Float_32;

    gsl_Ex:	Exception;
    error_code:	Integer;	-- of the last operation

    type Real_Function is access function (x: Real) return Real;

    procedure Integration_QNG
      (f:			Real_Function;
       a, b, epsabs, epsrel:	Real;
       result, abserr:		out Real;
       neval:			out Natural);

end GSL;
---------------------------------------------------------------------

Now when pass the type real as a generic parameter:

---------------------------------------------------------------------
generic
    type Real is digits <>;
when not used.
package GSL is
...
---------------------------------------------------------------------

and instanciate GSL with exactly the same type as above, I get a
STORAGE_ERROR : stack overflow or erroneous memory access.

I wrote a simpler example too, where just a function (gsl_bessl_j0) is 
called from the C library, and no function reference is passed as a 
parameter. This worked in the non-generic as well in the generic version.

For completeness, here follows the body of GSL

----------------------------------------------------------------------
with Interfaces.C;	use Interfaces;

package body GSL is

    type Void_Ptr is access all Integer;
    pragma Convention (C, Void_Ptr);

    type GSL_Inner_Function is
      access function (x: C.double; params: Void_Ptr) return C.double;
    pragma Convention (C, GSL_Inner_Function);

    type GSL_Function is record
       func:	GSL_Inner_Function;
       params:	Void_Ptr;
    end record;


    real_func:	Real_Function;

    ---------------------------------------------------------------------
    --	Auxiliary Subprograms
    ---------------------------------------------------------------------

    function func (x: C.double; params: Void_Ptr) return C.double;
    pragma Convention (C, func);

    function func (x: C.double; params: Void_Ptr) return C.double is
    begin return C.double (real_func (Real(x)));
    end func;


    function gsl_integration_qng
      (f: access GSL_Function;
       a, b, epsabs, epsrel: C.double;
       result, abserr: out C.double;
       neval: out C.size_t)
      return C.int;
    pragma Import (C, gsl_integration_qng,	"gsl_integration_qng");


    ---------------------------------------------------------------------
    -- Exported Subprograms
    ---------------------------------------------------------------------

    procedure Integration_QNG
      (f: Real_Function;
       a, b, epsabs, epsrel:	Real;
       result, abserr:		out Real;
       neval:			out Natural)
    is
       use type C.int;
       gslf:	aliased GSL_Function;
       status:	C.int;
       res, ae:	C.double;
       ne:	C.size_t;
    begin
       real_func:= f;
       gslf.func:= func'Access;
       gslf.params:= null;
       status:= gsl_integration_qng
	(gslf'Access,
	 C.double(a), C.double(b), C.double(epsabs), C.double(epsrel),
	 res, ae, ne);
       if status /= 0 then
	 error_code:= Integer (status);
	 raise gsl_Ex with
	   "gsl_integration_qng() returns error code " & C.int'Image(status);
       end if;
       result:= Real(res);
       abserr:= Real(ae);
       neval:= Natural(ne);
    end Integration_QNG;
----------------------------------------------------------------------

-- 
Frank Hrebabetzky		+49 / 6355 / 989 5070