Author:

• Name: Timo Poikola
  Location: FI - Republic of Finland (Finland)

To build:

    make

To use:

    ./prog

Try:

On a terminal that supports 24 bit color, has black background, and size at least 125x38, try:

    ./try.sh

Judges’ remarks:

It is said by some students of Astronomy:

Oh, Be A Fine Gal, Kiss Me!
Oh, Be A Fine Gentleman, Kiss Me!

Many Mnemonic variations exist. You might wish, on a star, to better understand the colors being displayed. And those in the deep south might wish to go north for a better view.

Author’s remarks:

How to build:

    cc -o prog -std=gnu11 -O3 prog.c

or

    make

Poster:

You can generate an A3 sized poster by make docs. This command creates a pdf file poikola.pdf.

Introduction:

It was a starry night when my wife pointed her finger up and asked: “What is this star and may I have some Easter eggs?”

So I had to sit down and solve those tricky questions with Nano and a C compiler.

NOTICE to those who wish for a greater challenge:

If you want a greater challenge, don’t read any further: just try to understand the program via the source.

If you get stuck, come back and read below for additional hints and information.

Little hints:

Basically, the program draws animated ASCII art of the Big Dipper using Annie Jump Cannon’s spectral classification system of stars and I think the colors of the output are as accurate as possible.

This program also tells once in a year if it is correct time to find and eat some Easter eggs.

The program has also at least three other functions, obvious and not so obvious.

Technical jargon

This program has been tested on xterm and Konsole and also Linux virtual terminal. Color support in the terminal is not necessary, but the effect is better with it.

This entry has partial support for terminals with a white background but the best viewing experience is achieved when the terminal in use supports 24-bit colors, has a black background and the size is at least 125x38.

Special note for Mac users: Terminal.app does not work as expected; you might need xterm from XQuartz, see the FAQ on “X11 on macOS”, or some other working terminal. Thanks to Dave Burton for spotting this problem.

The main reason for the header unistd.h is getdelim(3) but once I included it I also abused other functions and #defines. This header is mutually exclusive with -std=c11.

The program was developed with little-endian machines; I tried to support big-endian too, but this support is somewhat limited.

This program has been compiled with:

1. i386 (Debian Stretch) with gcc and clang
2. amd64 (Debian Buster) with gcc and clang
3. Raspberry Pi 3 (Debian stretch) with gcc and clang
4. Lego Mindstorms EV3 Intelligent Brick (Debian Jessie) with gcc and clang (in this case, compiling time with clang-3.5 12 seconds and with gcc 27 seconds)

Extra notes from the judges on the macOS Terminal.app problems:

Depending on the settings of the terminal in Terminal.app the program might not show anything at all. In other cases it won’t show all the colours right but mostly is okay. YMMV, as they say.

Warnings and restrictions required by law:

Please do not feed little babies chocolate.

Major hints:

I incorporated the Fletcher 16 checksum algorithm into the source for security reasons; it might be challenging to make changes without breaking the main functionality of the code.

The space after #define p return is necessary.

The computus (method to determine the date of Easter) uses an algorithm described in the journal Nature in 1876. It should be valid for Gregorian calendars.

Some obfuscation techniques used:

1. I tried to use meaningless or misleading variable names. For example, this program draws the Big Dipper with the correct colors, but variables like o, b, and a are used in totally unrelated tasks.
2. I reused and recycled variables almost every time when possible.
3. Unnecessary use of predefined stuff like __ATOMIC_SEQ_CST.
4. When I was a kid, my favorite programming language was Pascal. In Pascal, there are things like begin; and end; instead of curly brackets. They are used also in my code, but I had to shorten them to meet size requirements.
5. I also have strong Perl background, and therefore I added some dollar signs to the code. One of the first ideas was to write all variables with prefixed $, but then I rejected it.

If you think you understand how this program works, can you answer these questions:

1. What is the value of aI_ after line 21?
2. Why are there some big numbers on line 47?
3. How is the scaling effect created?
4. How do you change a single bit, without changing the functionality?

Rot18 part

Because the rot13 is too easy to decode with the plain eyes, I decided to use the Caesar cipher with the key 18:

Lzw xajkl tsffwj ak wfugvwv mkafy AWWW 754 xdgslk gf dafw 47. Al ak hjaflwv gfdq gf dalldw-wfvasf esuzafwk.

If you want to or must know and don’t know how to decipher this, you might look at the Caesar cipher decoder. Find the text that says:

Manual decryption and parameters Shift/Key (number)

.. and enter 18 and then click the button that says: DECRYPT (BRUTEFORCE).

Primary files

• prog.c - entry source code
• Makefile - entry Makefile
• prog.orig.c - original source code
• try.sh - script to try entry
• poikola.tex - supplied documentation in TeX format
• prog-doc.c - minor change to entry source code

Secondary files

• 2018_poikola.tar.bz2 - download entry tarball
• README.md - markdown source for this web page
• .entry.json - entry summary and manifest in JSON
• .gitignore - list of files that should not be committed under git
• .path - directory path from top level directory
• index.html - this web page

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