API(1) User Contributed Perl Documentation API(1)NAMEPDL::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.,
continuning 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.
SEE ALSO
PDL
Inline
BUGS
This manpage is still under development. Feedback and corrections are
welcome.
COPYRIGHT
Copyright (c) 2001, Christian Soeller. All Rights Reserved. This
module is free software. It may be used, redistributed and/or modified
under the same terms as PDL itself (see http://pdl.perl.org).
perl v5.10.0 2006-07-09 API(1)
