SV *
_smooth2( yp, wp, lambda_in, m )
         char * yp
         char * wp
         SV * lambda_in
         int m
   CODE:
{
  int i, i1, i2, ip;
  double c[MMAX+1], d[MMAX+1], e[MMAX+1],
        w[MMAX+1], y[MMAX+1], z[MMAX+1],
        lambda;
  double * ya;
  double * wa;
  ya = (double *) yp;
  wa = (double *) wp;
[download]

From perl, I call:

 
Smooth::_smooth2( $py, $pw, $lambda, scalar( @$yref ) );
[download]

Hope this helps,

Jeroen
"We are not alone"(FZ)
Update: Because the c-code sees only the pointers, no copy is made. To be sure, I tested it with a fresh module: TestMemXS:

#XS
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "unistd.h"
 
MODULE = TestMemXS              PACKAGE = TestMemXS
 
 
void
_test( yp )
         char * yp
 
   CODE:
{
  double * ya;
 
  ya = (double *) yp;
 
  sleep( 1000 );
}
-------------------
#testMemXS.pm
....
sub testMem{
  my $str = "\000" x 50e6;
  _test( $str );
}
....
-------------------
perl -MTestMemXS -e 'testMem()'
[download]

This stems from my (mistaken) belief that perl copies variables on subroutine calls. It appears that this is not true ;-). It seems that the copying may take place during the standard assignment in the subroutine body which can be avoided with a little thought. eg:

&find_index($key, \$bigstring);

sub find_index {
  my ($key, $rbigstring) = @_;

becomes:
&find_index($key, $bigstring);

sub find_index {
  my ($key) = $_[0];
  my ($rbigstring) = \$_[1];
 

This has the added benefit of making the sub call for both c and perl the same.

Thanks for your help

dino

Mmm thanks,
but if $pw is 50M in size then by not passing it as a ref, do the perl api routines convert it to a char * on every call?

dino

Perl does "pass by reference" already. No need to complicate things by taking a reference and passing that "by reference". So the above code does no copying and is really the simplest method.

        - tye (but my friends call me "Tye")

Maybe example 4 of the XStutorial can help you on - it looks good but I've never really done anything in XS before...

-- Hofmator

Thks,

This is what I've been looking at. The example doesn't use references, though example 6 does. I can try to meld both together so that I can call:

find_index($key, \$data);

I guess a lot depends on how SvPV works. If it copies the data then I need another method.

dino

I've got it to work with:

unsigned long
find_index (key, data)
        unsigned long         key
        SV    *               data
    INIT:
       STRLEN          datalen;
       char * s;
       if ((!SvROK(data))
          || (SvTYPE(SvRV(data)) != SVt_PV))
       {
          XSRETURN_UNDEF;
       }
       s = SvPV(SvRV(data), datalen);
    CODE:
      RETVAL = find_index (key, s, datalen);
    OUTPUT:
      RETVAL

I'm still not sure if SvPV copies its internal data somewhere or just returns a pointer to it.

Comments please

dino