Gregorian year/month/day to Julian year/day of year and reverse
conversion for the Hewlett-Packard 32SII hand held calculator

Author:  Leif Harcke <lharcke@stanford.edu>
Date: September 2003

References: Gregorian -> DOY uses algoritm from _Astronomical
Algorithms_ by Meeus attributed to U.S.  Naval Observatory
microcomputer almanac from 1978.  DOY -> Gregorian uses algorithm from
Meeus attributed to personal correspondence with ...

Use: XEQ G to find a Gregorian month/day given a day of year.  Program
displays YYYYPDOY to indicate intput format.  Press run/stop (R/S) and
program prompts for Julian dear/doy e.g. J?2003.254.  Enter a date/doy
and press R/S.  Program computes and displays Gregorian year/month/day
in format YYYY.MMDD.  XEQ J to find a Julian day number given a
Gregorian month and day.  Prompts and input are similar.

Variables:
  G = Gregorian date in YYYY.MMDD format
  Y = 4 digit Gregorian year
  M = month (range 1-12)
  D = day (range 1-31)
  J = Julian date in YYYY.DOY format
  N = day of year (range 1 - 366)
  K = 1 for bisextile (leap) year, 2 for common (non-leap) year

---- begin program listing ----
# Mnemonic G = Gregorian.  Entry point for computing Gregorian
# calendar date from Julian day number.
G01 LBL G
G02 SF 10           # show eqns as text
G03 EQN YYYYPDOY    # display input format e.g. 2003.260
G04 FIX 3           # use only 3 places after decimal
G05 INPUT J         # prompt user for Julian date
G06 IP              # integer part is yar
G07 STO Y
G08 XEQ L           # subroutine to test for leap year
G09 RCL J         
G10 FP              # fractional part of J is day of year
G11 1000
G12 *
G13 STO N
G14 1
G15 STO M
G16 32
G17 RCL N
G18 x<y?    # if day < 32 we are in Jan.
G19 GTO D   # so skip month computation
# Bytes: 48.5 Checksum: E996

# Mnemonic M = month.  Solve for month given leap year K and 
# day of year 
M01 LBL M
M02 RCL K
M03 +
M04 9
M05 *
M06 275
M07 /
M08 0.98
M09 +
M10 IP
M11 STO M
# Bytes: 32.5 Checksum: 0D1C

# Mnemonic D = day of month.  Solve for day of month.  Format and
# display Gregorian date.
D01 LBL D
D02 RCL N
D03 RCL M
D04 275
D05 *
D06 9
D07 /
D08 IP
D09 -
D10 RCL K
D11 RCL M
D12 9
D13 +
D14 12
D15 /
D16 IP
D17 *
D18 +
D19 30
D20 +
D21 STO D
D22 10000
D23 /       # divide day D by 10000 to put in output display
D24 RCL M
D25 100
D26 /       # divide month M by 100 to put in output display
D27 +
D28 RCL Y
D29 +       # add in year Y
D30 STO G
D31 FIX 4   # set display to 4 decimal places
D32 VIEW G  # view Gregorian date
D33 RTN     # end Julian to Gregorian conversion
# Bytes: 65.5 Checksum: A7BA

# Mnemonic J = Julian date.  Find Julian day of year for a Gregorian
# date.
J01 LBL J
J02 SF 10   # set flag to display equations as text
J03 EQN YYYYPMMDD  # display expected input format e.g. 2003.0917
J04 FIX 4   # use 4 decimal places in display
J05 INPUT G
J06 IP
J07 STO Y   # integer part is year
J08 XEQ L   # test for leap year and set K
J09 RCL G
J10 FP
J11 100
J12 *
J13 ENTER
J14 IP
J15 STO M
J16 -
J17 FP
J18 100
J19 *
J20 STO D
J21 RCL M
J22 275
J23 *
J24 9
J25 /
J26 IP
J27 RCL M
J28 9
J29 +
J30 12
J31 /
J32 IP
J33 RCL K
J34 *
J35 -
J36 RCL D
J37 +
J38 30
J39 -
J40 STO N
J41 1000
J42 /
J43 RCL Y
J44 +
J45 STO J
J46 FIX 3  # set display to 3 decimal places
J47 VIEW J # show year and day of year
J48 RTN    # end Gregorian to day of year conversion
# Bytes: 101.5 Checksum: 646A

# Mnemonic L = leapyear.  Subroutine to test for leap year.
# Inputs:
#  Y = Gregorian year (e.g. 2003)
# Outputs:
#  K = 1 for bisextile (leap) year, 2 for common (non-leap) year
L01 LBL L
L02 RCL Y   # get year
L03 400
L04 /
L05 FP
L06 x=0?
L07 GTO B   # if divisible by 400, is bixextile year
L08 RCL Y
L09 100
L10 /
L11 FP
L12 X=0?    
L13 GTO C   # else if divisible by 100 is common
L14 RCL Y
L15 4
L16 /
L17 FP
L18 x=0?    
L19 GTO B  # else if divisible by 4 is bisextile
           # else implied fallthrough to common year exit routine
# Bytes: 36.5 Checksum: 79BE

# Mnemonic C = common year.  
C01 LBL C   
C02 2
C03 STO K  # set K=2
C04 RTN    # return to main program
# Bytes: 6.0 Checksum: 9494

# Mnemonic B = bisextile year.
B01 LBL B
B02 1
B03 STO K  # set K=1
B04 RTN    # return to main program
# Bytes: 6.0 Checksum: C101

----end program listing----