VCRplus code Algorithm

[Ron Hansen]

I've been trying (without success) to crack the encryption scheme that
Gemstar uses in its' VCRplus codes.  I have written a TV/cable show
management system that generates plus codes for half-hour boundary shows
(ie 4 to 6 digit codes).  I can't seem to find anything on 7 and 8 digit
codes which handle 5 minute increments for program start time and
length.

(And yes, I have the article "Decoding a VCR Controller Code" by Ken
Shirriff, Curt Welch and Andrew Kinsman.  It was published in
Cryptologia.  Unfortunately, they didn't get beyond 6 digits either.)

BTW, this is strictly for my own use.  I'm just tired of approximating
shows and also a bug that I have that occasionally gives incorrect
results (I think it may be a leading zero being trimmed by the math
formulas).

Can anyone help?