#!/usr/bin/perl -w
use strict;

use Inline 'C', <<'END_C';

void _munge(
    char *outbuf,
    int   size,
    char *inbuf1,
    char *inbuf2 )
{
    double *output = (double *) outbuf;
    double *list1  = (double *) inbuf1;
    double *list2  = (double *) inbuf2;
    int i;
    for(  i= 0;  i < size;  ++i  ) {
        printf( "%f %f\n", list1[i], list2[i] );
        output[i]= list1[i] * list2[i];
    }
}

END_C


my $size = 3;
my $out  = "\0" x ( $size * length pack "d", 0.0 );
my $pack1= pack "d$size", 1, 2, 3;
my $pack2= pack "d$size", 4, 5, 6;
_munge( $out, $size, $pack1, $pack2 );
print $_, $/ for unpack "d$size", $out;

##</code><code>##

 $ perl double.pl
1.000000 4.000000
2.000000 5.000000
3.000000 6.000000
4
10
18