From: masa16.tanaka@...
Date: 2006-10-04T17:51:59+09:00
Subject: Re: need help with narray: how to return an array from a C-extension

Hi,

|From: "Joachim (M�nchen)"
> I am writing my first C extension module to ruby, and I need a little
> help:
> import of parameters works fine, but export of results not yet:

I recommend not to manipulate the C structure of NArray
because its structure is complicated and may be changed in future.

> static VALUE
> myarr_faltung1(VALUE m, VALUE distribution, VALUE lookuptable, VALUE
> mu_shifted)
> {
>     struct NARRAY *a1, *a2;
>     int mt, i;
>     volatile VALUE v1, v2;
> 
> /* import from parameters seems to work */
>     mt = NUM2INT(mu_shifted);
>     v1 = na_cast_unless_narray(distribution,NA_DFLOAT);
>     GetNArray(v1,a1);
>     v2 = na_cast_unless_narray(lookuptable,NA_DFLOAT);
>     GetNArray(v2,a2);
  // must check array sizes here

> /* calculation seems to work */
>     for (i=0; i<=1000; i++)
>         *((double*)(a1->ptr+i)) += *((double*)(a2->ptr+mt-i));
          *((double*)(a1->ptr)+i) += *((double*)(a2->ptr)+mt-i);
  // a1->ptr is declared as char*

> /* PROBLEM: this does not work. QUESTION: how can I overwrite the call
> parameter "distribution"
>     with a ruby array that contains the result a1->ptr of the above
> calculation? */
>     distribution = na_to_array( a1->ref );
  // I think ovewriting arguments is not a good idea.
  // If you cannot avoid it, overwrite RARRAY(distribution)->ptr[i] carefully.

> /* PROBLEM: the following does not work either. QUESTION: how can I
> return the result a1->ptr
>     of the above calculation to the calling program? */
>     return a1->ref ;
      return v1;

> }

Masahiro Tanaka