The computer control systems were dual, meaning two independent computer boards. The boards were designed independently, had different CPU architectures on board, were programmed in different languages, were developed by different teams, the algorithms used were different, and a third group would check that there was no inadvertent similarity.
An electronic comparator compared the results of the boards, and if they differed, automatically locked out both and alerted the pilot. And oh yea, there were dual comparators, and either one could lock them out.
This was pretty much standard practice at the time.
Note the complete lack of "we can write software that won't fail!" nonsense. This attitude permeates everything in airframe design, which is why air travel is so incredibly safe despite its inherent danger.
Thank you very much for taking the time to share and answer my question!