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<h1>The International Obfuscated C Code Contest</h1>
<h2>2019/poikola - Most calendrical</h2>
<h3>SHA and Prime and Fibonacci</h3>
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<a class="Left" href="../mills/index.html">← 2019/mills</a>
<a class="Left" href="../index.html">↑ 2019 ↑</a>
<a class="Left" href="../yang/index.html">2019/yang →</a>
<a class="Right" href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2019/poikola/prog.c">C code</a>
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<h2 id="author">Author:</h2>
<ul>
<li>Name: <a href="../../authors.html#Timo_Poikola">Timo Poikola</a><br>
Location: <a href="../../location.html#FI">FI</a> - <em>Republic of Finland </em> (<em>Finland</em>)</li>
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<h2 id="to-build">To build:</h2>
<pre><code> make</code></pre>
<p>There is an alternate version of this program which changes the way the output
is displayed. See <a href="#alternate-code">Alternate code</a> below.</p>
<p><strong>NOTE</strong>: we disable the optimiser because the author stated that for GCC optimiser
level 0 gave correct output. With clang <code>[0123s]</code> works which suggests that [123s]
might or might not work with GCC. Likewise, we do similar for the standard,
forcing <code>-std=gnu11</code>.</p>
<h3 id="bugs-and-misfeatures">Bugs and (Mis)features:</h3>
<p>The current status of this entry is:</p>
<blockquote>
<p><strong>STATUS: INABIAF - please DO NOT fix</strong></p>
</blockquote>
<p>For more detailed information see <a href="../../bugs.html#2019_poikola">2019/poikola in bugs.html</a>.</p>
<h2 id="to-use">To use:</h2>
<pre><code> ./prog 512 ./prog
sleep 86400; make clobber prog
./prog 512 ./prog
sleep 86400; make clobber prog
./prog 512 ./prog</code></pre>
<p>If you wish for some documentation:</p>
<pre><code> make docs</code></pre>
<p>This will create the file <code>poikola.pdf</code> for your enjoyment.</p>
<h2 id="try">Try:</h2>
<p>If you don’t have a few days, try:</p>
<pre><code> ./try.sh</code></pre>
<p>As the <a href="../../bugs.html#2019_poikola">2019/poikola in bugs.html</a> says, this program will not validate
input so it might get stuck or fail if invoked erroneously.</p>
<h2 id="alternate-code">Alternate code:</h2>
<p>This version prints a newline after each number for parsing in other ways than
what can be done with the original entry.</p>
<h3 id="alternate-build">Alternate build:</h3>
<pre><code> make alt</code></pre>
<h3 id="alternate-use">Alternate use:</h3>
<p>Use <code>prog.alt</code> as you would <code>prog</code> above.</p>
<h3 id="alternate-try">Alternate try:</h3>
<pre><code> ./try.alt.sh</code></pre>
<h2 id="judges-remarks">Judges’ remarks:</h2>
<p>Do you have the time to see what this program does? Think again, come back and
try again.</p>
<p>Note that <a href="https://t5k.org/curios/page.php/2.html">2</a> can be said to be the
least <a href="https://en.wikipedia.org/wiki/Parity_(mathematics)">odd</a>
<a href="https://en.wikipedia.org/wiki/Prime_number">prime</a> because it is the greatest
<a href="https://en.wikipedia.org/wiki/Parity_(mathematics)">even</a> prime. Moreover <code>2</code>
can be also said to be the greatest odd prime because it is the least even
prime.</p>
<p>The source code layout and some of the variable names honors the ski jumping
accomplishments of <a href="https://en.wikipedia.org/wiki/Matti_Nyk%C3%A4nen">Matti
Nykänen</a>.</p>
<h2 id="authors-remarks">Author’s remarks:</h2>
<h3 id="how-to-build">How to build:</h3>
<pre><code> gcc -O0 -o prog prog.c</code></pre>
<p>or</p>
<pre><code> clang -O[0123s] -o prog prog.c</code></pre>
<p>e.g.:</p>
<pre><code> clang -O1 -o prog prog.c</code></pre>
<h3 id="poster">Poster:</h3>
<p>You can generate an A3 sized poster by <code>make docs</code>. This command creates a pdf
file <code>poikola.pdf</code>. This requires the
<a href="https://en.wikipedia.org/wiki/PdfTeX">pdfTeX</a> tool.</p>
<h3 id="what-this-entry-does">What this entry does:</h3>
<p>An old wise man mumbled to me:</p>
<blockquote>
<p>Implement a program, which can calculate SHA-3 checksum for a file –</p>
</blockquote>
<p>I thought it was easy, but the wizard didn’t stop yet:</p>
<blockquote>
<p>and primes and Fibonacci numbers.</p>
</blockquote>
<p>Still easy. But the <a href="https://www.glyphweb.com/arda/g/gandalf.html">Gandalf the
Grey</a> impersonator was not ready:</p>
<blockquote>
<p>But use only <code>main()</code>, and do not use <code>math.h</code> nor predefined stuff at all.</p>
</blockquote>
<p>But wait, there are more rules: This work should reflect the extraordinary mind
of Matti Nykänen, the all-time best <a href="https://en.wikipedia.org/wiki/Matti_Nyk%C3%A4nen">ski
jumper</a> and <a href="http://telefinn.blogspot.com/2011/11/matti-nykanen-quotes.html">amateur
philosopher</a>,
who passed away on fourth of February 2019.</p>
<h3 id="oh-boys">Oh boys:</h3>
<p>So, I followed the rules given by <a href="https://www.glyphweb.com/arda/g/gandalf.html">Gandalf the
White</a> and the <a href="../../judges.html">Judges of
the IOCCC</a>.</p>
<p>Output of <code>iocccsize</code>, using the <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2019/iocccsize.c">2019 version of
iocccsize</a>, is carefully selected. For
the sake of clarity, I used single letter variables in the code. I also avoided
unnecessary use of functions. Like a
<a href="https://en.wikipedia.org/wiki/Tripundra">tripundra</a>, this program has three
levels. In order to reveal all of them, you have to compile this program on
three consecutive days.</p>
<p>As this is a contest for obfuscated code, the program does not perform
unnecessary checks, but either fails or gets stuck if invoked erroneously. The
program is invoked in this way:</p>
<pre><code> ./prog <integer> <file></code></pre>
<p>where <code><integer></code> is 224, 256, 384, 512 or even 1024. Yes, I know 1024 is not a
supported length of output, but as I said, the program does not validate its
input in any way. These same parameters should be given in calculating a
<a href="https://en.wikipedia.org/wiki/Fibonacci_sequence">Fibonacci sequence</a> or <a href="https://en.wikipedia.org/wiki/Prime_number">prime
numbers</a>. <em>Please note that maximum
file size is one gigabyte</em>!</p>
<h3 id="obfuscation">Obfuscation:</h3>
<p><em>Matti Nykänen</em>: Every time I jump, and I get that feeling of <em>bon voyage</em>,
the feeling that I’ve been here before.</p>
<p><em>Matti Nykänen</em>: When you are about to jump, you are all alone and have to
make your own decisions. Up there, it’s all <em>up yours</em>.</p>
<p>This code has some jumping too. I used some <code>goto</code>s instead of <code>longjmp(3)</code>. Some
Finnish <a href="https://en.wikipedia.org/wiki/Ski_jumping">ski jumping</a> sites are used
as labels, however, there is <code>lahti</code> instead of
<span style="font-family: monospace;">salpausselkä</span>.</p>
<h3 id="sha-3-512-compatibility-chart">SHA-3-512 Compatibility chart</h3>
<p>Tested against <a href="https://www.di-mgt.com.au/sha_testvectors.html">test vectors</a>.</p>
<p><code>Clang</code> (version 4.0): For optimization levels <code>[0123s]</code>, the program compiles and produces
correct output for every tested vector using the C standards c11, c89, c90, c99,
gnu11, gnu1x, gnu89, gnu90, gnu99, iso9899:1990, iso9899:199409, iso9899:1999
and iso9899:2011 (argument of <code>-std=</code>).</p>
<p><code>GCC</code> (version 6): For optimization level 0, correct output using the C
standards c11, c99, gnu11, gnu1x, gnu89, gnu90, gnu99, iso9899:1999 and
iso9899:2011.</p>
<h3 id="missing-a-prime">Missing a prime</h3>
<p>For obvious reason, the <a href="https://mathworld.wolfram.com/OddPrime.html">oddest
prime</a> is missing from output.</p>
<h3 id="observations">Observations</h3>
<p><code>gcc</code> and <code>clang</code> are very fragile compilers. I spent numerous hours trying to
achieve exactly the same output from different optimization levels and
compilers. Small change in code can produce really unexpected results, i.e. the
compiler can skip a few expressions or statements without obvious reason.</p>
<h3 id="notice-to-those-who-wish-for-a-greater-challenge">NOTICE to those who wish for a greater challenge:</h3>
<p><strong>If you want a greater challenge, don’t read any further</strong>:
just try to understand the program via the source.</p>
<p>If you get stuck, come back and read below for additional hints and information.</p>
<h3 id="how-this-entry-works">How this entry works:</h3>
<p>It is commonly believed that <a href="http://www.cadaeic.net/calendar.htm">Mike Keith’s
algorithm</a> published in <em>Journal of
Recreational Mathematics</em>, Vol. 22, No. 4, 1990, p. 280, is the shortest way to
calculate the day of the week for a given date.</p>
<h4 id="keiths-versus-my-algorithm">Keith’s versus my algorithm</h4>
<p>Kieth’s algorithm is <code>(d+=m<3?y--:y-2,23*m/9+d+4+y/4-y/100+y/400)%7</code>. I noticed
that <code>(23*m/9+(m<3?y--:y-2)+d+4+y/4-y/100+y/400)%7</code> is one character shorter. In
my solution, <code>m<3?y--:y-2</code> is used directly, instead of assigning a value to
<code>d</code>.</p>
<p><code>Q</code> is pronounced in Finnish exactly like <code>kuu</code>, a word for
<a href="https://en.wikipedia.org/wiki/Month">month</a> or the
<a href="https://en.wikipedia.org/wiki/Moon">Moon</a>. So, <code>Q = k</code> is intended.</p>
<p>Last term of outputted <a href="https://en.wikipedia.org/wiki/Fibonacci_sequence">Fibonacci
sequence</a> is the last one
smaller than 2<sup>64</sup>. It is a plain but funny coincidence
that the value of <code>^</code> is 94 in <a href="https://en.wikipedia.org/wiki/ASCII">ASCII</a>.</p>
<p>For <a href="https://en.wikipedia.org/wiki/Prime_number">prime calculations</a>: I recycled
code from my high school C-programming course. Originally, I wrote it over 20
years ago. My teacher said that it is (too) complicated to use bits stored in
arrays, so I did it.</p>
<h3 id="other-stuff">Other stuff</h3>
<p><a href="../../authors.html#Cody_Boone_Ferguson">Cody Boone Ferguson</a>: I really like that you enjoyed my
previous entry. I hope that you will like this entry too. Because I did not
want to give too many clues to <a href="../../judges.html">the Judges</a>, I tried to write this
entry in a different way than <a href="../../2018/poikola/index.html">Most Stellar</a>, but in this
code there is at least one recycled thing from it. By the way, the answers to
the questions I posed: (1) 255. (2) Try to compare binary representations of
those <code>float</code>s and binary representation of the string “<code>25th IOCCC!</code>”. (3) I
don’t know. I used standard <a href="https://en.wikipedia.org/wiki/Trigonometric_functions">trigonometric
functions</a> from
<a href="https://en.wikipedia.org/wiki/C_mathematical_functions#Overview_of_functions">math.h</a>
for rotating the <a href="https://en.wikipedia.org/wiki/Big_Dipper">Big Dipper</a> and
later replaced those functions with my own implementations. But there was a bug
in my code and the effect was more beautiful than intended. I did not even
debug this bug and now it works as a feature. (4) It is not possible. If you
change a single bit, the <a href="https://en.wikipedia.org/wiki/Fletcher%27s_checksum#Fletcher-16">Fletcher’s 16
checksum</a> does
not match anymore and <code>goto</code> jumps to the end of the code.</p>
<p>I see that one of the <a href="../../authors.html#Volker_Diels-Grabsch">Volker
Diels-Grabsch</a>’s winning entries is
awarded the category <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2019/diels-grabsch2/prog.c">Most self-aware</a>. In last
year, my entry incorporates the <a href="https://en.wikipedia.org/wiki/Fletcher%27s_checksum#Fletcher-16">Fletcher’s 16
algorithm</a> to
ensure integrity of code. One of my first ideas for this year was to do the same
thing, but with <a href="https://en.wikipedia.org/wiki/SHA-3">SHA-3</a>. Using Fletcher 16,
calculating a <a href="https://en.wikipedia.org/wiki/Checksum">checksum</a> which matches
with <code>sleeping time factor</code> took about one minute. I realized that SHA-3 even
with 224-<a href="https://en.wikipedia.org/wiki/Bit">bit</a> output could take too much
<a href="https://en.wikipedia.org/wiki/Central_processing_unit">CPU</a> time.</p>
<p>I would like to say <em>thanks</em> to PSP, because there were not too many
interruptions during the coding phase.</p>
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