Re: Lepton EDA 1.9.14 announce and misc questions

[Vladimir Zhbanov]

Hi Matt,

On Tue, Apr 20, 2021 at 06:46:27AM -0700, Matt Wette wrote:
> 
> 
> On 4/20/21 5:47 AM, Matt Wette wrote:
> > 
> > 
> > On 4/20/21 2:29 AM, Vladimir Zhbanov wrote:
> > > Hi Guile users and devs,
> > > 
> > > I'm the current maintainer of Lepton EDA suite, an about five year
> > > old fork of geda-gaf with accent to moving more functionality to
> > > Scheme code.  I'm not sure if it is acceptable to advertise it
> > > here, please let me know if not.  I just know several Guix
> > > packagers are reading this mailing list and would like to announce
> > > a new version of Lepton, 1.9.14 has been released on April, 7:
> > > 
> > > https://github.com/lepton-eda/lepton-eda/releases/tag/1.9.14-20210407
> > > 
> > > 
> > 
> > Sweet.  Thanks for posting this.   I will take a look at your problem.
> > It'll require digging into the eda_..._dirs function.
> > 
> > 
> > 
> The following should work as a complete program on a system w/ glib.
> You need to first convert the result to a bytevector and then access the
> elements (pointers) one at a time.  Note that we don't know how big the
> array returned from the C function is.  I pick an oversized value of 100.
> 
> (use-modules (system foreign))
> (use-modules (rnrs bytevectors))
> 
> (define glib (dynamic-link "libglib-2.0"))
> 
> (define g-get-system-data-dirs
>   (let ((f (pointer->procedure
>         '* (dynamic-func "g_get_system_data_dirs" glib) (list)))
>     (bv-pointer-ref (cond
>              ((= (sizeof '*) 8) bytevector-u64-native-ref )
>              ((= (sizeof '*) 4) bytevector-u32-native-ref )
>              (else (error "hmmm"))))
>     (BIG 100))
>     (lambda ()
>       (let* ((r (f))
>          (p (pointer->bytevector r (* BIG (sizeof '*)))))
>         (let loop ((ix 0))
>           (let* ((ad (bv-pointer-ref p ix))
>              (sp (make-pointer ad)))
>         (if (equal? %null-pointer sp)
>             '()
>             (cons (pointer->string sp) (loop (+ ix (sizeof '*)))))))))))
> 
> (simple-format #t "~S" (g-get-system-data-dirs))

Thank you for your replies!

Probably, I missed something here, so I'll try to elaborate a bit
on my initial question.  The function eda_get_system_data_dirs()
mentioned in my first message has the same type, is defined the
same way using dynamic-func though in liblepton instead of glib,
and works on mostly the same array as glib's
g_get_system_data_dirs().  The function I've shown works well and
outputs the same results as yours.  It simply uses a bit more
upper level interface, IIUC.  So the first question is: I wonder,
if using bytevectors directly adds something here?

Another issue is a little more confusing for me.  I read in
several places that even on the same system different compilators,
say gcc and g++, may use different alignment even for basic C
types like, say, double.  What will they do on different platforms
then?  May it be that (alignof '*) will be twice greater than
(sizeof '*)?  In such a case using multiplied sizeof of pointer
for searching the location of a pointer in memory would be just
dangerous.  I used sizeof in the first version of my code but
started to doubt if it is correct and how portable it is.

Thanks,
  Vladimir