(HP 41 CV/CX, DM41) Date of Easter sunday

[rawi]

Find the Date of Easter Sunday for any year between 1583 and 9999.

I was somewhat surprised not to find an existing program to do this. The only program I found is finding more religious days and is longer. So I made the following solution. Enjoy!

Application:
XEQ Alpha EASTER Alpha -> YEAR? -> Put in year, e.g. 2024 R/S -> 3103.2024
Interpretation: Easter Sunday in 2024 was 31st of March.
Registers used: 00-12
Source for algorithm:
Duffet-Smith, P.: Practical astronomy with your calculator, 3rd ed., Cambridge 1979, p. 3

Code:

LBL ‘EASTER
    ‘YEAR?
    PROMPT
    STO 00
    19 
    MOD
    STO 01
    RCL 00
    100
10  MOD
    STO 03
    RCL 00
    100
    /
    INT
    STO 02
    4
    /    
    INT
20  STO 04
    RCL 02
    4
    MOD
    STO 05
    RCL 02
    8
    +
    25
    /
30  INT
    STO 06
    CHS
    RCL 02
    +
    1
    +
    3
    /
    INT
40  STO 07
    CHS
    RCL 01
    19
    *
    +
    RCL 02
    +
    RCL 04
    -
50  15
    +
    30
    MOD
    STO 08
    RCL 03
    4
    /
    INT
    STO 09
60  RCL 03
    4
    MOD
    STO 10
    CHS
    X<>Y
    RCL 05
    +
    2
    *
70  +
    32
    +
    RCL 08
    -
    7
    MOD
    STO 11
    22
    *
80  RCL 08
    11
    *
    +
    RCL 01
    +
    451
    /
    INT
    STO 12
90  7
    *
    CHS
    RCL 08
    +
    RCL 11
    +
    114
    +
    ENTER
100 ENTER
    31
    /
    INT
     X<>Y
    31
    MOD
    1
    +
    100
110 *
    +
    RCL 00
    10000
    /
    +
    FIX 4
    RTN
118 END