Throw Away Your C Compiler (after building Perl):

#!/usr/bin/perl

 # P5NCI.t

 BEGIN
{
    chdir 't' if -d 't';
    use blib;
}

 use strict;
use warnings;

 use Test::More tests => 9;

 use_ok('P5NCI') or exit;

 my $double_lib    = P5NCI::load_lib( '../nci_demo.so' );
 my $double_double = P5NCI::load_nci_func( $double_lib, 'double_double', 'dd' );
is( $double_double->( 1.0 ),  2.0  );
is( $double_double->( 3.14 ), 6.28 );

 my $double_int = P5NCI::load_nci_func( $double_lib, 'double_int', 'ii' );
is( $double_int->( 1 ), 2 );
is( $double_int->( 3 ), 6 );

 my $double_float = P5NCI::load_nci_func( $double_lib, 'double_float', 'ff' );
is( $double_float->( 1.0 ),   2.0   );
ok( abs( $double_float->( 0.314 ) - 0.628) < 0.00001 );

 my $multiply_ints = P5NCI::load_nci_func( $double_lib, 'multiply_ints', 'iii' );
is( $multiply_ints->( 10, 20 ), 200 );
is( $multiply_ints->(  5,  5 ),  25 );

The interface is a bit grotty, the documentation is spotty, the build system needs some help, and it only handles really simple functions right now, but it works.