Algorithms
The actual algorithms used to encode and decode the TV guide values from and to their time representations were published in 1992, but only for 6 digit codes or less.
Several open source code 6 digit examples are available. An implementation using Excel macros is also available.
One problem found during reverse engineering efforts is that the algorithm seemed to change for seven and eight digit codes.
Although not well known, code that also works with 7 and 8 digit codes was posted anonymously in 2003. The source code for the full 8 digits was written in C and later converted to Perl.
Read more about this topic: Video Recorder Scheduling Code