sub gf2 {
    my ($spectrum, $subsp) = @_;
    my %unique;
    
    @unique{@spectrum} = ();
    
    my @uspectrum = sort {$a <=> $b} keys %unique;
    
    return gf1(\@uspectrum, $subsp);
}


sub gf1 {
    my ($spectrum, $subsp) = @_;
    my $sum = 0;

    for my $value (@$subsp) {
        my $mid = int (@$spectrum / 2);
        my $span = int (@$spectrum / 2);
        
        while (int $span) {
            if ($value < $spectrum->[$mid]) {
                $mid -= int (($span /= 2) + 0.5);
            } elsif ($value > $spectrum->[$mid]) {
                $mid += int (0.5 + ($span /= 2));
            } else {
                last;
            }
        }
        
        my $delta;
        my $left = $mid ? abs ($value - $spectrum->[$mid - 1]) : 1e6;
        my $right = $mid < $#$spectrum ? abs ($value - $spectrum->[$mid + 1]) : 1e6;
        my $cent = abs ($value - $spectrum->[$mid]);
        $sum += (sort {$a <=> $b} ($left, $right, $cent))[0];
    }

    my $result = 1000;
    $result = @$subsp / $sum if $sum != 0;
    
    return $result;
}