Gregorian Calendar for the HP-32SII

For the HP-33S version, go here.

Written by Dave Coffin in March 2006.

Overview

Program C converts a calendar date from the format yyyy.mmdd to a simple day count. Program G does the exact opposite. Months go from 01 to 12, and days from 01 to 31. Years must not be truncated to two digits!!

These operations are useful for any problem that depends on the exact interval between two dates.

Usage

2006.0310       Today's date (Mar 10, 2006)
XEQ C
732685
1965.0927       Your birthdate (Sep 27, 1965)
XEQ C
717911
-
14774		Your age in days
LASTx
717911		When will you be 20000 days old?
20000
+
737911
XEQ G
2020.063 
FIX 4
2020.0630	June 30, 2020

In my system, Day 0 is March 1, 0 A.D (better known as 1 B.C.), or Julian day 1721120. Thus at 12:00 noon Universal Time on March 10, 2006, the Julian day was 1721120 + 732685 = 2453805.0.

Divide a day number by seven and take the remainder to determine the weekday. Zero is Wednesday.

Listing of Program C

C01 LBL C
C02 22			; stash 0.88 for RCL+ later
C03 25
C04 ÷
C05 STO Y
C06 R↓
C07 ENTER		; copy the whole date
C08 FP			; discard the year
C09 0.0301
C10 x>y?		; move New Year's Day from January 1 to March 1
C11 RCL+ Y
C12 x<>y
C13 R↓
C14 -	
C15 STO Y		; save the new date
C16 FP			; month and day in Xreg
C17 STO- Y		; keep year only in Y
C18 100
C19 ×
C20 ENTER		; split month and day
C21 FP
C22 100
C23 ×
C24 x<>y
C25 IP			; Yreg = day, Xreg = month
C26 153			; convert month to days
C27 ×
C28 5
C29 ÷
C30 2
C31 1/x
C32 +
C33 IP
C34 +
C35 365.25		; convert year to days
C36 RCL× Y
C37 IP
C38 +
C39 RCL Y
C40 100			; centuries are not leap years...
C41 ÷
C42 IP
C43 -
C44 LASTx		; ...except those divisible by 400
C45 4
C46 ÷
C47 IP
C48 +
C49 RTN

checksum = 1058, length = 89.5

Listing of Program G

G01 LBL G
G02 ENTER
G03 ENTER
G04 10
G05 ×
G06 9
G07 +
G08 365242.5		; how many whole centuries?
G09 ÷
G10 IP			; add one missing leap day per century
G11 +
G12 LASTx		; except for centuries divisible by 400
G13 4
G14 ÷
G15 IP
G16 -
G17 ENTER
G18 ENTER
G19 10
G20 ×
G21 9
G22 +
G23 3652.5		; compute the year
G24 ÷
G25 IP
G26 STO Y
G27 365.25		; keep the remaining days
G28 ×
G29 IP
G30 -
G31 2			; determine month and day
G32 1/x
G33 +
G34 5
G35 ×
G36 153
G37 ÷
G38 ENTER
G39 FP
G40 153
G41 ×
G42 5
G43 ÷
G44 IP
G45 1
G46 +
G47 100
G48 ÷
G49 x<>y
G50 IP
G51 +			; Xreg contains mm.dd
G52 88
G53 x<> Y		; move New Year's Day from March 1 to January 1
G54 x<>y
G55 10
G56 x≤y?		; "≤" means "less than or equal to"
G57 RCL+ Y
G58 +
G59 7
G60 -
G61 100			; combine mm.dd value with year
G62 ÷
G63 +
G64 RTN

checksum = 8A5D, length = 120.0