#!/usr/bin/perl
use strict;
use warnings;
$>++;

# get 500 random ip adresses, see genip code below
my %need;
open IP, "./genip |" or die "ooeps $!\n";

for (1..500) {
    my ($a, $b, $c, $d)=split /\./, <IP>;
    $need{$a}{$b}{$c}{$d}++;
}

for (1..10_000_000) {
     my $ip=<IP>;
     my ($a, $b, $c, $d)=split /\./, $ip;
     # the compiler may optimise this line ... 
     # next unless exists $need{$a}{$b}{$c}{$d};
     # so all the following can probably be replaced
     # but it is too late for me to benchmark, g'night
     next unless exists $need{$a};
     next unless exists $need{$a}{$b};
     next unless exists $need{$a}{$b}{$c};
     print "a.b.c\n"; # see how sparse we are !
     next unless exists $need{$a}{$b}{$c}{$d};
     print "match ! $ip\n";
}
close IP;

__END__
# Random IP address generator used above ...

#!/usr/bin/perl
use strict;
use warnings;

while (1) {
    my $ip = int rand 256;
    for (1..3) {
        $ip.= "." . int rand 256;
    }
    print $ip, $/;
}