code: def in6_cidr2mask(m):
      
      if m > 128 or m < 0:
          raise Kamene_Exception("value provided to in6_cidr2mask outside [0, 128] domain (%d)" % m)
  
      t = []
      for i in range(0, 4):
          t.append(max(0, 2**32  - 2**(32-min(32, m))))
          m -= 32
  
      return b"".join([ struct.pack('!I', i) for i in t ])
docs: Return the mask (bitstring) associated with provided length 
      value. For instance if function is called on 48, return value is
      '\xff\xff\xff\xff\xff\xff\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'.