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.IX Title "CallExt 3pm"
.TH CallExt 3pm 2024-04-25 "perl v5.38.2" "User Contributed Perl Documentation"
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.SH NAME
PDL::CallExt \- call functions in external shared libraries
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 2
\& use PDL::CallExt;
\& callext(\*(Aqfile.so\*(Aq, \*(Aqfoofunc\*(Aq, $x, $y); # pass ndarrays to foofunc()
\&
\& % perl \-MPDL::CallExt \-e callext_cc file.c
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\fBcallext()\fR loads in a shareable object (i.e. compiled code) using
Perl's dynamic loader, calls the named function and passes a list of
ndarray arguments to it.
.PP
It provides a reasonably portable way of doing this, including
compiling the code with the right flags, though it requires simple
perl and C wrapper routines to be written. You may prefer to use PP,
which is much more portable. See PDL::PP. You should definitely use
the latter for a 'proper' PDL module, or if you run in to the
limitations of this module.
.SH API
.IX Header "API"
\&\fBcallext_cc()\fR allows one to compile the shared objects using Perl's knowledge
of compiler flags.
.PP
The named function (e.g. 'foofunc') must take a list of ndarray structures as
arguments, there is now way of doing portable general argument construction
hence this limitation.
.PP
In detail the code in the original file.c would look like this:
.PP
.Vb 3
\& #include "pdlsimple.h" /* Declare simple ndarray structs \- note this .h file
\&                           contains NO perl/PDL dependencies so can be used
\&                           standalone */
\&
\& int foofunc(int nargs, pdlsimple **args); /* foofunc prototype */
.Ve
.PP
i.e. \fBfoofunc()\fR takes an array of pointers to pdlsimple structs. The use is
similar to that of \f(CW\*(C`main(int nargs, char **argv)\*(C'\fR in UNIX C applications.
.PP
pdlsimple.h defines a simple N\-dimensional data structure which looks like this:
.PP
.Vb 7
\&  struct pdlsimple {
\&     int    datatype;  /* whether byte/int/float etc. */
\&     void  *data;      /* Generic pointer to the data block */
\&     PDL_Indx nvals;   /* Number of data values */
\&     PDL_Indx *dims;   /* Array of data dimensions */
\&     PDL_Indx ndims;   /* Number of data dimensions */
\&  };
.Ve
.PP
(PDL_Indx is 32\- or 64\-bit depending on architecture and is defined in pdlsimple.h)
.PP
This is a simplification of the internal representation of ndarrays in PDL which is
more complicated because of broadcasting, dataflow, etc. It will usually be found
somewhere like /usr/local/lib/perl5/site_perl/PDL/pdlsimple.h
.PP
Thus to actually use this to call real functions one would need to write a wrapper.
e.g. to call a 2D image processing routine:
.PP
.Vb 1
\& void myimage_processer(double* image, int nx, int ny);
\&
\& int foofunc(int nargs, pdlsimple **args) {
\&    pdlsimple* image = pdlsimple[0];
\&    myimage_processer( image\->data, *(image\->dims), *(image\->dims+1) );
\&    ...
\& }
.Ve
.PP
Obviously a real wrapper would include more error and argument checking.
.PP
This might be compiled (e.g. Linux):
.PP
.Vb 1
\& cc \-shared \-o mycode.so mycode.c
.Ve
.PP
In general Perl knows how to do this, so you should be able to get
away with:
.PP
.Vb 1
\& perl \-MPDL::CallExt \-e callext_cc file.c
.Ve
.PP
\&\fBcallext_cc()\fR is a function defined in PDL::CallExt to generate the
correct compilation flags for shared objects.
.PP
If their are problems you will need to refer to you C compiler manual to find
out how to generate shared libraries.
.PP
See t/callext.t in the distribution for a working example.
.PP
It is up to the caller to ensure datatypes of ndarrays are correct \- if not
peculiar results or SEGVs will result.
.SH FUNCTIONS
.IX Header "FUNCTIONS"
.SS callext
.IX Subsection "callext"
Call a function in an external library using Perl dynamic loading
.PP
.Vb 1
\&  callext(\*(Aqfile.so\*(Aq, \*(Aqfoofunc\*(Aq, $x, $y); # pass ndarrays to foofunc()
.Ve
.PP
The file must be compiled with dynamic loading options
(see \f(CW\*(C`callext_cc\*(C'\fR). See the module docs \f(CW\*(C`PDL::Callext\*(C'\fR
for a description of the API.
.SS callext_cc
.IX Subsection "callext_cc"
Compile external C code for dynamic loading
.PP
Usage:
.PP
.Vb 1
\& % perl \-MPDL::CallExt \-e callext_cc file.c \-o file.so
.Ve
.PP
This works portably because when Perl has built in knowledge of how to do
dynamic loading on the system on which it was installed.
See the module docs \f(CW\*(C`PDL::Callext\*(C'\fR for a description of
the API.
.SH AUTHORS
.IX Header "AUTHORS"
Copyright (C) Karl Glazebrook 1997.
All rights reserved. There is no warranty. You are allowed
to redistribute this software / documentation under certain
conditions. For details, see the file COPYING in the PDL
distribution. If this file is separated from the PDL distribution,
the copyright notice should be included in the file.