Most stellar

Timo Poikola ioccc2018@ig.fi
https://ig.fi/

Judges' comments:

To use:

make

./prog

Try:

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

./prog

Selected 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 comments:

How to build

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

make

Poster

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

What this entry does

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.

Little spoilers

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 does not work as expected you might need xterm from XQuartz or some other working terminal. Thanks to Dave Burton for spotting this problem.

The main reason for the header unistd.h is getdelim() 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 in

i386 (Debian Stretch) with gcc and clang
amd64 (Debian Buster) with gcc and clang
Raspberry Pi 3 (Debian stretch) with gcc and clang
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)

Warnings and restrictions required by law

Please do not feed little babies chocolate.

Major spoilers

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 uses an algorithm described in the journal Nature in 1876. It should be valid for Gregorian calendars.

Some obfuscation techniques used

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.
I reused and recycled variables almost every time when possible.
Unnecessary use of predefined stuff like __ATOMIC_SEQ_CST.
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.
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:

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

Rot18ed 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.