A interactive LDPC decoder, written as a proof-of-understanding of the Product/Sum algorithm.
This implements the example in the paper "Introducing Low-Density Parity-Check Codes" by Sarah J Johnson.
https://www.researchgate.net/publication/228977165_Introducing_Low-Density_Parity-Check_Codes
It displays a help screen on startup, detailing the keystrokes.