If I understand your requirements correctly, you are trying to see if a given IP address is part of a class C (or a derivative of that problem: which of a particular Class-C address is missing).

The NetAddr::IP module contains several functions that can help:

• $me->contains($other)
  Returns true when $me completely contains $other. False is returned otherwise and undef is returned if $me and $other are not both NetAddr::IP objects.
• ->network()
  Returns a new object refering to the network address of a given subnet. A network address has all zero bits where the bits of the netmask are zero. Normally this is used to refer to a subnet.
• ->hostenum()
  Returns the list of hosts within a subnet.

When dealing with IP addresses, this module will significantly reduce development time, improve readability, and decrease bugs. At least, it did, for me.