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lookup. The hash table used linear probing which got very slow as the hash table got full. Using std::map is about 10 times faster. The hash table was slow enough that it took the majority of the time for me in an ARP scan of a single address. # nmap -sP 192.168.0.190 mac_prefix_init took 0.49261 s. Nmap done: 1 IP address (1 host up) scanned in 0.59 seconds # nmap -sP 192.168.0.190 mac_prefix_init took 0.04392 s. Nmap done: 1 IP address (1 host up) scanned in 0.13 seconds The memory usage of std::map is probably greater. The hash table used 19037 pointers and about 13000 structures of size 8 (on a 32-bit architecture), or about 176 KB. Assuming the map has left, right, and parent pointers, and a red-black indicator per node, the usage is 16 bytes per prefix plus 8 bytes for the structure data, or 304 KB total. But this makes fingerdiff so much faster, I want to leave it in place at least until this round of OS integration is done.
Here is some documentation for Nmap, but these files are much less comprehensive than what you'll find at the actual Nmap documentation site ( http://nmap.org ).