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Current exclusions list from --excludefile takes linear time to match against. Using a trie structure, we can do matching in O(log n) time, with a hard maximum of 32 comparisons for IPv4 and 128 comparisons for IPv6. Each node of the trie represents an address prefix that all subsequent nodes share; matching stops when one is matched exactly or when the candidate address does not match any prefix of the addresses in the trie. For now, only numeric addresses without netmask are supported. We plan to extend this to addresses with netmasks, including resolved names. Storing IPv4 ranges and wildcards in this structure would be prohibitively complex, so the existing linear match method will be used for those. It is unlikely that any users are using large exclusion lists of these types of specifications, so performance impact is small. Potential future features could use the trie structure to implement custom routing or scope-limiting. This was a todo list item based on this report: https://seclists.org/nmap-dev/2012/q4/420
Nmap 
Nmap is released under a custom license, which is based on (but not compatible with) GPLv2. The Nmap license allows free usage by end users, and we also offer a commercial license for companies that wish to redistribute Nmap technology with their products. See Nmap Copyright and Licensing for full details.
The latest version of this software as well as binary installers for Windows, macOS, and Linux (RPM) are available from Nmap.org
Full documentation is also available on the Nmap.org website.
Questions and suggestions may be sent to the Nmap-dev mailing list.
Installing
Ideally, you should be able to just type:
./configure
make
make install
For far more in-depth compilation, installation, and removal notes, read the Nmap Install Guide on Nmap.org.
Using Nmap
Nmap has a lot of features, but getting started is as easy as running nmap scanme.nmap.org. Running nmap without any parameters will give a helpful
list of the most common options, which are discussed in depth in the man
page. Users who prefer a graphical interface
can use the included Zenmap front-end.
Contributing
Information about filing bug reports and contributing to the Nmap project can be found in the HACKING and CONTRIBUTING.md files.