Faster factor finder method for 42S

[Joe Horn]

(11-29-2019 01:25 PM)grsbanks Wrote:  

(11-29-2019 01:12 PM)Joe Horn Wrote:  For the record, the 3 hidden HP-42S functions were discovered in a Jack in the Box fast-food eatery (23812 El Toro Rd, Lake Forest, California 92630) while eating a cheeseburger, on 9 November 1988. Museums always seek historical context, so there it is.

Absolutely! Does anyone still know exactly how they were discovered? They're not mentioned in the manual as far as I remember, they don't appear in the function catalog and they don't appear in the matrix menu either. Did someone have access to a ROM listing or something?

I remember how they were discovered, because it was quite thrilling. I used the 42S's built-in memory hex browser/editor (AKA "debugger") to find where programs were stored, then poked every possible hex value into program memory and exited to normal program mode to see what the corresponding commands were. That's how I created the 42S Hex Table (which also appears in that issue of HPX Exchange) and discovered the "hidden functions" lurking in there. What those functions do, and how to use them, was then a matter of trial and error, turbo-powered by a Jack in the Box cheeseburger.