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;
}

##</code><code>##

gf1 result: 2.11267605633804
gf2 result: 2.11267605633804
op result: 2.11267605633804

      Rate      op     gf2     gf1
op  7.57/s      --   -100%   -100%
gf2 7732/s 102012%      --    -10%
gf1 8582/s 113238%     11%      --

##</code><code>##

use warnings;
use strict;
use Benchmark qw(cmpthese);

my @spectrum = qw/174.0 102.99 71.62 70.53 82.49 69.05 18.94 102.99 71.62 70.53 82.49 69.05 18.94 102.99 71.62 70.53 82.49 69.05 18.94 102.99 71.62 70.53 82.49 69.05 18.94/;
my @subsp = qw(102.0 18.94 71.61 82.0 173.0 68.7);
my %unique;

@unique{@spectrum} = ();

my @uspectrum = sort {$a <=> $b} keys %unique;

print "gf1 result: ", gf1(\@uspectrum, \@subsp), "\n";
print "gf2 result: ", gf2(\@spectrum, \@subsp), "\n";
print "op result: ", op(\@subsp, \@spectrum, 3), "\n\n";


cmpthese (-5,
        {
        gf1 => sub {gf1(\@uspectrum, \@subsp)},
        gf2 => sub {gf1(\@spectrum, \@subsp)},
        op => sub {op(\@subsp, \@spectrum, 3)},
        }
    );

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;
}

sub op {
    my ($request, $spectrum, $limit) = @_[0..3];

    my @spectrum = @$spectrum;
    my @request  = sort {$a <=> $b} @$request;

    return 0, [] unless @request;
    return 0, [] if @spectrum < @request;
   
    my %good;
    foreach my $signal (@request) {
        my @good;
        return 0 unless (@good = grep { abs($_-$signal) <= $limit } @spectrum);
        %good = (%good, map { ($_ => 1) } @good);
    }
    @spectrum = sort {$a <=> $b} grep { $good{$_} } @spectrum;
   
    my $alpha;
    my $best_subsp;
    my $alphabeta;
    $alphabeta = sub {
        my ($beta, $spectrum, $subsp, $found) = @_;
        unless (@$subsp) {
            $alpha = $beta;
            $best_subsp = $found;
            return;
        }

        my $compared = $subsp->[0];
        foreach my $sign_id (0..$#{$spectrum}) {
            my $diff = abs($spectrum->[$sign_id] - $compared);
            next if $diff > $limit;
            next if defined($alpha) && ($diff + $beta) >= $alpha;
            $alphabeta->($diff + $beta,
                [@{$spectrum}[0..$sign_id-1, $sign_id+1..$#{$spectrum}]],
                [@{$subsp}[1..$#{$subsp}]],
                [@$found, $spectrum->[$sign_id]],
            );
        }
        return;
    };
    $alphabeta->(0, \@spectrum, \@request, []);

    return 0 unless defined $alpha;
    return $alpha ? @request/$alpha : 1000;    
}