Back to index

---

DDAYS and DATE+ for the HP-42S

Original date functions by Christoph Giesselink repackaged by Erik Ehrling (e.g. added type checking).

This is an implementation of the two date functions DDAYS and DATE+ from the HP-48 which calculates the number of days between two dates (DDAYS) and adds/subtracts a number of days to a given date (DATE+). All dates within the Gregorian calendar from the start the 15th October 1582 up to the 31st December 9999 are supported.

Note: This version hides the underlying functions D2J and J2D. If you are interested in these functions you'd be better of with the full package of date functions

Usage:

DDAYS:
Enter two dates on the stack
Y: start date (format mm.ddyyyy)
X: end date (format mm.ddyyyy)
and then run DDAYS. The result will be the number of days between the start date and the end date.


DATE+:
Y: original date (format mm.ddyyyy)
X: number of days to add (positive or negative)
and then run DATE+. The result will be the original date + given number of days (on the format mm.ddyyyy)


Technical notes:

The program is built up around two functions for converting a Gregorian date into a Julian date (LBL 08 in the program) and a Julian date into a Gregorian date (LBL 10) based on algorithms by R. G. Tantzen. Around these functions is a wrapper that does validation of the input, converts dates into their Julian representation, does the subtraction or addition and then converts back into Gregorian format.

References:
Robert G. Tantzen: "Algorithm 199: Conversions between calendar date and Julian day number" in Communications of the ACM, Volume 6, Issue 8 (August 1963)

Binary files for emulators:
Raw binary: date.raw  Binary for HP-42X: date.42x

---

---

Generated by 42s2html - 31 January 2004, 12:03