my @arrr = split //, unpack "B*", $bitvec;
my $histogram = Math::GSL::Vector->new();
my $sequence = Math::GSL::Vector->new( \@arrr );

while (($pos,$freq) = each %points) {
    my $view = gsl_vector_subvector( $sequence, 4 * $pos, 4 * $slen );

    $histogram += $view * $freq;
    $sum_freq += $freq;
}

# normalize and uninterleave
$histogram *= 1 / $sum_freq;
@parts = part { $i++ % 4 } $histogram->as_list;