The code in the file printhex.asm is based on code shared by Dirk Wolfgang Glomp on StackOverflow at https://stackoverflow.com/a/22897576. since he shared this code there in 2014, it is covered by the Creative Commons CC BY-SA 3.0 license. See also https://stackoverflow.com/help/licensing
Quoting the relevant part in the README file:
It's free, do with it what you will. I don't particularly care.
Feel free to contact me with questions and improvements.
- Jeff Leyda, 2 September 2002