#   convert {start_ip, end_ip} into prefix notation
#
#   Tatsuya Mori 

def inet_aton ip
  ip.split(/\./).map{|c| c.to_i}.pack("C*").unpack("N").first
end

def inet_ntoa n
  [n].pack("N").unpack("C4").join(".")
end

def get_forward_prefixes(s,e)
  prefixes = []
  while s <= e
    len = 32 - ((Math.log(e - s + 1) / Math.log(2)).to_i).floor
    prefixes << "#{inet_ntoa(s)}/#{len}"
    s = s + 2 ** (32 - len)
  end
  return prefixes
end

def get_backward_prefixes(s,e)
  prefixes = []
  while s <= e
    len = 32 - ((Math.log(e - s + 1) / Math.log(2)).to_i).floor
    prefix = inet_ntoa(e - 2 ** (32 - len) + 1)
    prefixes << "#{prefix}/#{len}"
    e = e - 2 ** (32 - len) 
  end
  return prefixes.reverse
end

def get_prefixes(s, e)
  return [] if e < s
  prefixes = []
  if (s & 0x000000ff == 0) 
    prefixes = get_forward_prefixes(s,e)
  else
    if (e & 0xffffff00) > (s & 0xffffff00) 
      prefixes = 
        get_backward_prefixes(s, (e & 0xffffff00) - 1) +
        get_forward_prefixes(e & 0xffffff00, e)
    else
      l = e - s + 1
      base = s & 0xffffff00
      width = 2 ** ((Math.log(l) / Math.log(2)).to_i.floor - 1)
      i = 0
      while i < (s & 0x000000ff)
        i += width
      end
      prefixes = 
        get_backward_prefixes(s, base + i - 1) + 
        get_forward_prefixes(base + i, e)
    end
  end
  return prefixes
end

start_ip = (ARGV[0] || "192.168.5.0")
end_ip = (ARGV[1] || "192.168.5.254")

puts "#{start_ip} - #{end_ip}"
puts "---"
puts get_prefixes(inet_aton(start_ip),inet_aton(end_ip)).join("\n")