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PDL-2.4.9_012
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/ PDL::API

NAME

PDL::API - making piddles from Perl and C/XS code

DESCRIPTION

A simple cookbook how to create piddles manually. It covers both the Perl and the C/XS level. Additionally, it describes the PDL core routines that can be accessed from other modules. These routines basically define the PDL API. If you need to access piddles from C/XS you probably need to know about these functions.

SYNOPSIS

use PDL;
sub mkmypiddle {
 ...
}

Creating a piddle manually from Perl

Sometimes you want to create a piddle manually from binary data. You can do that at the Perl level. Examples in the distribution include some of the IO routines. The code snippet below illustrates the required steps.

use Carp;
sub mkmypiddle {
  my $class = shift;
  my $pdl  = $class->new;
  $pdl->set_datatype($PDL_B);
  my @dims = (1,3,4);
  my $size = 1;
  for (@dims) { $size *= $_ }
  $pdl->setdims([@dims]);
  my $dref = $pdl->get_dataref();

  # read data directly from file
  open my $file, '<data.dat' or die "couldn't open data.dat";
  my $len = $size*PDL::Core::howbig($pdl->get_datatype);
  croak "couldn't read enough data" if
    read( $file, $$dref, $len) != $len;
  close $file;
  $pdl->upd_data();

  return $pdl;
}

Creating a piddle in C

The following example creates a piddle at the C level. We use the Inline module which is really the way to interface Perl and C these days. Note the use of the PDL_INCLUDE, PDL_TYPEMAP, PDL_AUTO_INCLUDE and PDL_BOOT functions that were imported from PDL::Core::Dev. They are used in conjunction with an Inline Config call to ensure that the PDL typemap, the PDL include files and the PDL Core routines are found during compilation and later runtime execution.

use PDL::LiteF;
use PDL::Core::Dev;

$a = myfloatseq(); # exercise our C piddle constructor

print $a->info,"\n";

# the reason for this config call is explained below
use Inline C => Config =>
  INC           => &PDL_INCLUDE,  # make sure we find pdlcore.h etc
  TYPEMAPS      => &PDL_TYPEMAP,  # use the PDL typemap
  AUTO_INCLUDE  => &PDL_AUTO_INCLUDE,  # global declarations and includes
  BOOT          => &PDL_BOOT;     # boot code to load the Core struct

use Inline C;
Inline->init; # useful if you want to be able to 'do'-load this script

__DATA__

__C__

static pdl* new_pdl(int datatype, PDL_Long dims[], int ndims)
{
  pdl *p = PDL->pdlnew();
  PDL->setdims (p, dims, ndims);  /* set dims */
  p->datatype = datatype;         /* and data type */
  PDL->allocdata (p);             /* allocate the data chunk */

  return p;
}

pdl* myfloatseq()
{
  PDL_Long dims[] = {5,5,5};
  pdl *p = new_pdl(PDL_F,dims,3);
  PDL_Float *dataf = (PDL_Float *) p->data;
  int i;

  for (i=0;i<5*5*5;i++)
    dataf[i] = i; /* the data must be initialized ! */
  return p;
}

Wrapping your own data into a piddle

Sometimes you obtain a chunk of data from another source, for example an image processing library, etc. All you want to do in that case is wrap your data into a piddle struct at the C level. Examples using this approach can be found in the IO modules (where FastRaw and FlexRaw use it for mmapped access) and the Gimp Perl module (that uses it to wrap Gimp pixel regions into piddles). The following script demonstrates a simple example:

   use PDL::LiteF;
   use PDL::Core::Dev;
   use PDL::Graphics::PGPLOT;

   $b = mkpiddle();

   print $b->info,"\n";

   imag1 $b;

   use Inline C => Config =>
     INC           => &PDL_INCLUDE,
     TYPEMAPS      => &PDL_TYPEMAP,
     AUTO_INCLUDE  => &PDL_AUTO_INCLUDE,
     BOOT          => &PDL_BOOT;

   use Inline C;
   Inline->init;

   __DATA__

   __C__

   /* wrap a user supplied chunk of data into a piddle
    * You must specify the dimensions (dims,ndims) and 
    * the datatype (constants for the datatypes are declared
    * in pdl.h; e.g. PDL_B for byte type, etc)
    *
    * when the created piddle 'npdl' is destroyed on the
    * Perl side the function passed as the 'delete_magic'
    * parameter will be called with the pointer to the pdl structure
    * and the 'delparam' argument.
    * This gives you an opportunity to perform any clean up
    * that is necessary. For example, you might have to
    * explicitly call a function to free the resources
    * associated with your data pointer.
    * At the very least 'delete_magic' should zero the piddle's data pointer:
    * 
    *     void delete_mydata(pdl* pdl, int param)
    *     {
    *       pdl->data = 0;
    *     }
    *     pdl *p = pdl_wrap(mydata, PDL_B, dims, ndims, delete_mydata,0);
    *
    * pdl_wrap returns the pointer to the pdl
    * that was created.
    */
   typedef void (*DelMagic)(pdl *, int param);
   static void default_magic(pdl *p, int pa) { p->data = 0; }
   static pdl* pdl_wrap(void *data, int datatype, PDL_Long dims[],
			int ndims, DelMagic delete_magic, int delparam)
   {
     pdl* npdl = PDL->pdlnew(); /* get the empty container */

     PDL->setdims(npdl,dims,ndims); /* set dims      */
     npdl->datatype = datatype;     /* and data type */
     npdl->data = data;             /* point it to your data */
     /* make sure the core doesn't meddle with your data */
     npdl->state |= PDL_DONTTOUCHDATA | PDL_ALLOCATED;
     if (delete_magic != NULL)
       PDL->add_deletedata_magic(npdl, delete_magic, delparam);
     else
       PDL->add_deletedata_magic(npdl, default_magic, 0);
     return npdl;
   }

   #define SZ 256
   /* a really silly function that makes a ramp image
    * in reality this could be an opaque function
    * in some library that you are using
    */
   static PDL_Byte* mkramp(void)
   {
     PDL_Byte *data;
     int i;

     if ((data = malloc(SZ*SZ*sizeof(PDL_Byte))) == NULL)
       croak("mkramp: Couldn't allocate memory");
     for (i=0;i<SZ*SZ;i++)
       data[i] = i % SZ;

     return data;
   }

   /* this function takes care of the required clean-up */
   static void delete_myramp(pdl* p, int param)
   {
     if (p->data)
       free(p->data);
     p->data = 0;
   }

   pdl* mkpiddle()
   {
     PDL_Long dims[] = {SZ,SZ};
     pdl *p;

     p = pdl_wrap((void *) mkramp(), PDL_B, dims, 2, 
		  delete_myramp,0); /* the delparam is abitrarily set to 0 */
     return p;
   }

The gory details

The Core struct -- getting at PDL core routines at runtime

PDL uses a technique similar to that employed by the Tk modules to let other modules use its core routines. A pointer to all shared core PDL routines is stored in the $PDL::SHARE variable. XS code should get hold of this pointer at boot time so that the rest of the C/XS code can then use that pointer for access at run time. This initial loading of the pointer is most easily achieved using the functions PDL_AUTO_INCLUDE and PDL_BOOT that are defined and exported by PDL::Core::Dev. Typical usage with the Inline module has already been demonstrated:

use Inline C => Config =>
  INC           => &PDL_INCLUDE,
  TYPEMAPS      => &PDL_TYPEMAP,
  AUTO_INCLUDE  => &PDL_AUTO_INCLUDE, # declarations
  BOOT          => &PDL_BOOT;         # code for the XS boot section

The code returned by PDL_AUTO_INCLUDE makes sure that pdlcore.h is included and declares the static variables to hold the pointer to the Core struct. It looks something like this:

  print PDL_AUTO_INCLUDE;

#include <pdlcore.h>
static Core* PDL; /* Structure holds core C functions */
static SV* CoreSV;       /* Gets pointer to Perl var holding core structure */

The code returned by PDL_BOOT retrieves the $PDL::SHARE variable and initializes the pointer to the Core struct. For those who know their way around the Perl API here is the code:

  print PDL_BOOT;

  perl_require_pv ("PDL::Core"); /* make sure PDL::Core is loaded */
  CoreSV = perl_get_sv("PDL::SHARE",FALSE);  /* SV* value */
#ifndef aTHX_
#define aTHX_
#endif
  if (CoreSV==NULL)
    Perl_croak(aTHX_ "We require the PDL::Core module, which was not found");
  PDL = INT2PTR(Core*,SvIV( CoreSV ));  /* Core* value */
  if (PDL->Version != PDL_CORE_VERSION)
    Perl_croak(aTHX_ "The code needs to be recompiled against the newly installed PDL");

The Core struct contains version info to ensure that the structure defined in pdlcore.h really corresponds to the one obtained at runtime. The code above tests for this

if (PDL->Version != PDL_CORE_VERSION)
  ....

For more information on the Core struct see PDL::Internals.

With these preparations your code can now access the core routines as already shown in some of the examples above, e.g.

pdl *p = PDL->pdlnew();

By default the C variable named PDL is used to hold the pointer to the Core struct. If that is (for whichever reason) a problem you can explicitly specify a name for the variable with the PDL_AUTO_INCLUDE and the PDL_BOOT routines:

use Inline C => Config =>
  INC           => &PDL_INCLUDE,
  TYPEMAPS      => &PDL_TYPEMAP,
  AUTO_INCLUDE  => &PDL_AUTO_INCLUDE 'PDL_Corep',
  BOOT          => &PDL_BOOT 'PDL_Corep';

Make sure you use the same identifier with PDL_AUTO_INCLUDE and PDL_BOOT and use that same identifier in your own code. E.g., continuing from the example above:

pdl *p = PDL_Corep->pdlnew();

Some selected core routines explained

The full definition of the Core struct can be found in the file pdlcore.h. In the following the most frequently used member functions of this struct are briefly explained.

  • pdl *SvPDLV(SV *sv)

  • pdl *SetSV_PDL(SV *sv, pdl *it)

  • pdl *pdlnew()

    pdlnew returns an empty pdl object that needs further initialization to turn it into a proper piddle. Example:

    pdl *p = PDL->pdlnew();
PDL->setdims(p,dims,ndims);
p->datatype = PDL_B;

  • pdl *null()

  • SV *copy(pdl* p, char* )

  • void *smalloc(int nbytes)

  • int howbig(int pdl_datatype)

  • void add_deletedata_magic(pdl *p, void (*func)(pdl*, int), int param)

  • void allocdata(pdl *p)

  • void make_physical(pdl *p)

  • void make_physdims(pdl *p)

  • void make_physvaffine(pdl *p)

  • void qsort_X(PDL_Xtype *data, int a, int b) and void qsort_ind_X(PDL_Xtype *data, int *ix, int a, int b)

    where X is one of B,S,U,L,F,D and Xtype is one of Byte, Short, Ushort, Long, Float or Double.

  • float NaN_float and double NaN_double

    These are constants to produce the required NaN values.

  • void pdl_barf(const char* pat,...) and void pdl_warn(const char* pat,...)

    These are C-code equivalents of barf and warn. They include special handling of error or warning messages during pthreading (i.e. processor multi-threading) that defer the messages until after pthreading is completed. When pthreading is complete, perl's barf or warn is called with the deferred messages. This is needed to keep from calling perl's barf or warn during pthreading, which can cause segfaults.

    Note that barf and warn have been redefined (using c-preprocessor macros) in pdlcore.h to PDL->barf and PDL->warn. This is to keep any XS or PP code from calling perl's barf or warn directly, which can cause segfaults during pthreading.

    See PDL::ParallelCPU for more information on pthreading.

SEE ALSO

PDL

Inline

BUGS

This manpage is still under development. Feedback and corrections are welcome.

COPYRIGHT

Copyright 2010 Christian Soeller (c.soeller@auckland.ac.nz). You can distribute and/or modify this document under the same terms as the current Perl license.

See: http://dev.perl.org/licenses/