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

void _munge( char *outlist, int size, char *inlist1, char *inlist2 )
{
    double *output = (double *) outlist;
    double *list1  = (double *) inlist1;
    double *list2  = (double *) inlist2;
    /* use the "arrays" just like normal for C code: */
    int i;
    for( i= 0; i < size; ++i ) {
        output[i] = combine( list1[i], list2[i] );
    }
}

END_C

sub munge {
    my( $l1, $l2 ) = @_;
    my $size = 0+@$l1;
    my $out = "\0" x ( $size * length pack "d", 0.0 );
    my $pack1 = pack "d$size", @$l1;
    my $pack2 = pack "d$size", @$l2;
    _munge( $out, $size, $pack1, $pack2 );
    return unpack "d$size", $out;
}