#!/usr/bin/perl -w
use strict;
$|++;

use Socket qw(inet_aton inet_ntoa);

sub cidr2bits {
  my $cidr = shift;
  my ($addr, $maskbits) = $cidr =~ /^([\d.]+)\/(\d+)$/
    or die "bad format for cidr: $cidr";
  
  substr(unpack("B*", inet_aton($addr)), 0, $maskbits);
}

sub bits2cidr {
  my $bits = shift;
  
  inet_ntoa(pack "B*",
            substr("${bits}00000000000000000000000000000000", 0, 32))
    . "/" . length($bits);
}

sub mergecidr {
  local $_ = join "", sort map { cidr2bits($_)."\n" } @_;
  1 while s/^(\d+)0\n\1[1]\n/$1\n/m or s/^(\d+)\n\1\d+\n/$1\n/m;
  map bits2cidr($_), split /\n/;
}

my @first = qw(
               209.152.214.112/30
               209.152.214.116/31
               209.152.214.118/31
              );

my @second = qw(
                209.152.214.112/30
                209.152.214.116/32
                209.152.214.118/31
               );

my @third = qw(
               209.152.214.112/31
               209.152.214.116/31
               209.152.214.118/31
              );

if (1) {

  print join "----\n", map
    join("",
         "from:\n", map("  $_\n", @$_),
         "to:\n", map("  $_\n", mergecidr(@$_))),
           \@first, \@second, \@third;

}
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