This repository supplies ipv4 sets for analysis and filtering
purposes. The bulk of the code resides in the library, libbitset. This
contains routimes for creating bitset variables for adding both
individual IPv4 addresses and IPv4 cidr blocks to them.  It is
possible to save bitsets to files and to load them from files created
by the save routine. It is also possible to compare bit sets for
equality.  A routine for describing a bitset based on its internal
structure is also included.

Programs to create bitsets from an ascii text file and to list a
bitset as an ascii text file are also included.

Internally, the implementation uses an array of 512 pointers to /9
cidr blocks as its top level. Both Full and Empty /9s are completely
represented at this level.  Partially full /9s are represented by
pointers to a block of 512 /18 cidr blocks.  At this level, there are
also 512 pointers with full and empty /18s being designated by
distinguished pointer values.  A partially full /18 is represented by
a block of 2^14 bits or 512 32bit words, each word representing a /27.

Externally, a bitset is represented by
1) a header that contains housekeeping information such as the total
   number of addresses in the set, the number of full and parital /9s
   and /18s, etc.
2) The prefixes for full /9 blocks, if any
3) The prefixes for full /18 blocks, if any
4) Full and partial /27 sequences consisting of
   a) a 32 bit header with a 27 bit /27 prefix, a bit to indicate
      whether the sequence consnsts of full or partial /27s, and a 4
      bit count (interpreted as 1-16) of the /27s covered by the
      sequence. If the /27s are full, no detail blocks are needed.
   b) If the sequence contasins partial blocks, up to 16 detail
      blocks, each representing a bitmap for a /27 follow the header
      block. 

John McHugh - RedJack, LLC
March 2012