NAME

FFI::Platypus::Lang::Fortran - Documentation and tools for using Platypus with Fortran

SYNOPSIS

Fortran 77:

 C Fortran function that adds two numbers together
 C On Linux create a .so with: gfortran -shared -o libadd.so add.f
       FUNCTION ADD(IA, IB)
           ADD = IA + IB
       END

Fortran 90/95:

 ! Fortran function that adds two numbers together
 ! On Linux create a .so with: gfortran -shared -o libadd.so add.f90
 function add(a,b) result(ret)
   implicit none
   integer :: a
   integer :: b
   integer :: ret
   ret = a + b
 end function add

Perl:

 use FFI::Platypus;
 $ffi->lang('Fortran');
 $ffi->lib('./libadd.so'); # or add.dll on Windows
 
 # Fortran is pass by reference, so use pointers
 $ffi->attach( add => [ 'integer*', 'integer*' ] => 'integer' );
 
 # Use a reference to an integer to pass
 # a pointer to an integer
 print add(\1,\2), "\n";  # prints 3

DESCRIPTION

This module provides native types and demangling for Fortran when used with FFI::Platypus.

This module is somewhat experimental. It is also available for adoption for anyone either sufficiently knowledgable about Fortran or eager enough to learn enough about Fortran. If you are interested, please send me a pull request or two on the project's GitHub.

For types, _ is used instead of *, so use integer_4 instead of integer*4.

byte, character
integer, integer_1, integer_2, integer_4, integer_8
unsigned, unsigned_1, unsigned_2, unsigned_4, unsigned_8
logical, logical_1, logical_2, logical_4, logical_8
real, real_4, real_8, double precision

CAVEATS

Fortran is pass by reference, which means that you need to pass pointers. Confusingly Platypus uses a star (*) suffix to indicate a pointer, and Fortran uses a star to indicate the size of types.

This module currently uses and is bundled with a fork of ExtUtils::F77 called Module::Build::FFI::Fortran::ExtUtilsF77. It is used to probe for a Fortran compiler, which can be problematic if you want to bundle Fortran 90 or Fortran 95 code, as it only knows about Fortran 77. On some platforms (such as those using gfortran) the same command is invoked to build all versions of fortran. On some (usually those with a f77 command) a f90 or f95 command is required to build code for newer versions of Fortran. We attempt to work around these limitations.

METHODS

Generally you will not use this class directly, instead interacting with the FFI::Platypus instance. However, the public methods used by Platypus are documented here.

native_type_map

 my $hashref = FFI::Platypus::Lang::Fortran->native_type_map;

This returns a hash reference containing the native aliases for Fortran. That is the keys are native Fortran types and the values are libffi native types.

mangler

 my $mangler = FFI::Platypus::Lang::Fortran->mangler($ffi->libs);
 my $c_name = $mangler->($fortran_name);

Returns a subroutine reference that will "mangle" Fortran names.

EXAMPLES

Call a subroutine

Fortran:

 C Compile with gfortran -shared -o libsub.so sub.f
       SUBROUTINE ADD(IRESULT, IA, IB)
           IRESULT = IA + IB
       END

Perl:

 use FFI::Platypus;
 
 my $ffi = FFI::Platypus->new;
 $ffi->lang('Fortran');
 $ffi->lib('./libsub.so');
 
 $ffi->attach( add => ['integer*','integer*','integer*'] => 'void');
 
 my $value = 0;
 add(\$value, \1, \2);
 
 print "$value\n";

Discussion: A Fortran "subroutine" is just a function that doesn't return a value. In Fortran 77 variables that start wit the letter I are integers unless declared otherwise. Fortran is also pass by reference, which means under the covers Fortran passes its arguments as pointers to the data, and you have to remember to pass in a reference to a value in Perl in cases where you would normally pass in a simple value to a C function.

Call Fortran 90 / 95

Fortran:

 ! on Linux: gfortran -shared -fPIC -o libfib.so fib.f90
 
 recursive function fib(x) result(ret)
   integer, intent(in) :: x
   integer :: ret
   
   if (x == 1 .or. x == 2) then
     ret = 1
   else
     ret = fib(x-1) + fib(x-2)
   end if
 
 end function fib

Perl:

 use FFI::Platypus;
 
 my $ffi = FFI::Platypus->new;
 $ffi->lang('Fortran');
 $ffi->lib('./libfib.so');
 
 $ffi->attach( fib => ['integer*'] => 'integer' );
 
 for(1..10)
 {
   print fib(\$_), "\n";
 }

Discussion: Fortran 90 has "advanced" features such as recursion and pointers, which can now be used in Perl too.

Complex numbers

Fortran:

 ! on Linux: gfortran -shared -fPIC -o libcomplex.so complex.f90
 
 subroutine complex_decompose(c,r,i)
   implicit none
   complex*16 :: c
   real*8 :: r
   real*8 :: i
   
   r = real(c)
   i = aimag(c)
 
 end subroutine complex_decompose

Perl:

 use FFI::Platypus;
 use Math::Complex;
 
 my $ffi->lang('Fortran');
 my $ffi->lib('./libcomplex.so');
 
 $ffi->attach(
   complex_decompose => ['real_8[2]','real_8*','real_8*'] => 'void',
   sub {
     # wrapper around the Fortran function complex_decompose
     # $decompose is a code ref to the real complex_decompose
     # and $complex is the first argument passed int othe Perl
     # function complex_decompose
     my($decompose, $complex) = @_;
     my $real;
     my $imaginary;
     # decompose the Perl complex number and pass it as a
     # Fortran complex number
     $decompose->([Re($complex),Im($complex)], \$real, \$imaginary);
     # The decomposed real and imaginary parts are returned from
     # Fortran.  We pass them back to the caller as a return value
     ($real, $imaginary);
   },
 );
 
 my($r,$i) = complex_decompose(1.5 + 2.5*i);
 
 print "${r} + ${i}i\n";

Discussion: More recent versions of libffi and FFI::Platypus support complex types, but not pointers to complex types, so they aren't (yet) much use when calling Fortran, which is pass by reference. There is a work around, however, at least for complex types passes as arguments. They are really two just two real*4 or real*8 types joined together like an array or record of two elements. Thus we can pass in a complex type to a Fortran subroutine as an array of two floating points. Take care though, as this technique DOES NOT work for return types.

From my research, some Fortran compilers pass in the return address of the return value as the first argument for functions that return a complex type. This is not the case for Gnu Fortran, the compiler that I have been testing with, but if your compiler does use this convention you could pass in the "return value" as a two element array, as we did in the above example. I have not been able to test this though.

Fixed length array

Fortran:

 ! on Linux: gfortran -shared -fPIC -o libfixed.so fixed.f90
 
 subroutine print_array10(a)
   implicit none
   integer, dimension(10) :: a
   integer :: i
   do i=1,10
     print *, a(i)
   end do
 end subroutine print_array10

Perl:

 use FFI::Platypus;
 
 my $ffi = FFI::Platypus->new;
 $ffi->lang('Fortran');
 $ffi->lib('./libfixed.so');
 
 $ffi->attach( print_array10  => ['integer[10]'] => 'void' );
 my $array = [5,10,15,20,25,30,35,40,45,50];
 print_array10($array);

Output:

            5
           10
           15
           20
           25
           30
           35
           40
           45
           50

Discussion: In Fortran arrays are 1 indexed unlike Perl and C where arrays are 0 indexed. Perl arrays are passed in from Perl using Platypus as a array reference.

Multidimensional arrays

Fortran:

 ! On Linux gfortran -shared -fPIC -o libfixed2.so fixed2.f90
 
 subroutine print_array2x5(a)
   implicit none
   integer, dimension(2,5) :: a
   integer :: i,n
   
   do i=1,5
     print *, a(1,i), a(2,i)
   end do
 end subroutine print_array2x5

Perl:

 use FFI::Platypus;
 
 my $ffi = FFI::Platypus->new;
 $ffi->lang('Fortran');
 $ffi->lib('./libfixed.so');
 
 $ffi->attach( print_array2x5 => ['integer[10]'] => 'void' );
 my $array = [5,10,15,20,25,30,35,40,45,50];
 print_array2x5($array);

Output:

            5          10
           15          20
           25          30
           35          40
           45          50

Discussion: Perl does not generally support multi-dimensional arrays (though they can be achieved using lists of references). In Fortran, multidimensional arrays are stored as a contiguous series of bytes, so you can pass in a single dimensional array to a Fortran function or subroutine assuming it has sufficent number of values.

Platypus updates any values that have been changed by Fortran when the Fortran code returns.

One thing to keep in mind is that Fortran arrays are "column-first", which is the opposite of C/C++, which could be termed "row-first".

Variable-length array

Fortran:

 ! On Linux gfortran -shared -fPIC -o libvar.so var.f90
 
 function sum_array(size,a) result(ret)
   implicit none
   integer :: size
   integer, dimension(size) :: a
   integer :: i
   integer :: ret
   
   ret = 0
   
   do i=1,size
     ret = ret + a(i)
   end do
 end function sum_array

Perl:

 use FFI::Platypus;
 
 my $ffi = FFI::Platypus->new;
 $ffi->lang("Fortran");
 $ffi->lib("./libvar_array.so");
 
 $ffi->attach( sum_array => ['integer*','integer[]'] => 'integer',
   sub {
     my $f = shift;
     my $size = scalar @_;
     $f->(\$size, \@_);
   },
 );
 
 my @a = (1..10);
 my @b = (25..30);

 print sum_array(1..10), "\n";
 print sum_array(25..30), "\n";

Output:

 55
 165

Discussion: Fortran allows variable-length arrays. To indicate a variable length array use the [] notation without a length. Note that this works for argument types, where Perl knows the length of an array, but it will not work for return types, where Perl has no way of determining the size of the returned array (you can probably fake it with an opaque type and a wrapper function though).

SUPPORT

If something does not work as advertised, or the way that you think it should, or if you have a feature request, please open an issue on this project's GitHub issue tracker:

https://github.com/plicease/FFI-Platypus-Lang-Fortran/issues

CONTRIBUTING

If you have implemented a new feature or fixed a bug then you may make a pull reequest on this project's GitHub repository:

https://github.com/plicease/FFI-Platypus-Lang-Fortran/pulls

Also Feel free to use the issue tracker:

https://github.com/plicease/FFI-Platypus-Lang-Fortran/issues

This project's GitHub issue tracker listed above is not Write-Only. If you want to contribute then feel free to browse through the existing issues and see if there is something you feel you might be good at and take a whack at the problem. I frequently open issues myself that I hope will be accomplished by someone in the future but do not have time to immediately implement myself.

Another good area to help out in is documentation. I try to make sure that there is good document coverage, that is there should be documentation describing all the public features and warnings about common pitfalls, but an outsider's or alternate view point on such things would be welcome; if you see something confusing or lacks sufficient detail I encourage documentation only pull requests to improve things.

Caution: if you do this too frequently I may nominate you as the new maintainer. Extreme caution: if you like that sort of thing.

SEE ALSO

FFI::Platypus

The Core Platypus documentation.

Module::Build::FFI::Fortran

Bundle Fortran with your FFI / Perl extension.

AUTHOR

Graham Ollis <plicease@cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2015 by Graham Ollis

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

This software comes bundled with a forked version of ExtUtils::F77 called Module::Build::FFI::Fortran::ExtUtilsF77. ExtUtils::F77 comes with this statement regarding its license:

  Copyright (c) 2001 by Karl Glazebrook. All rights reserved.  This distribution 
  is free software; you can redistribute it and/or modify it under the same 
  terms as Perl itself.

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  OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  ARE DISCLAIMED.  IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
  DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
  IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  POSSIBILITY OF SUCH DAMAGE.

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  FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
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