Date addition: can it be done in a single HP 65 program card?

[teenix]

On the HP Museum USB stick, there is a HP67 Calendar Pac with a program called Days to Dates, Dates to Days. You can set a date and number of days from that date to compute a new date. It might give some ideas for the 65.

cheers

Tony

(01-01-2020 09:49 PM)Dave Britten Wrote:  The HP 65 Finance Pac has a nice program for calculating the number of days between dates, but it doesn't include any programs for adding days to compute a future (or past) date. Can this be done within 100 steps - and without hand-entering constants - on a 65? The days-between-dates program appears to be doing something similar to calculating a Julian day number for the two input dates and taking the difference. My attempts to adapt a Julian day number program from a different model typically end up with most of memory filled, and nowhere near enough left for a Julian-day-to-MM.DDYYYY routine.

I know a good chunk of steps can be saved by having the user input separate month, day, and year (via storing into three registers, using three of the subroutine keys, or simply breaking up the date on the stack), so that the program doesn't have to do all the INT/FRAC grunt work to parse input in MM.DDYYYY format, but that still doesn't seem to get close enough.

I don't need a program with broad enough range to calculate the date 3 million days after Mt. Vesuvius destroyed Pompeii or anything like that; I would think 1900 - 2099 is a perfectly adequate range for most financial calculations. If the HP 80 can do this, I would think the 65 ought to be able to as well.