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<h1>The International Obfuscated C Code Contest</h1>
|
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<h2>2004/vik2 - Best abuse of CPP</h2>
|
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<h3>Calculates prime numbers using only CPP</h3>
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<h2 id="author">Author:</h2>
|
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<ul>
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<li>Name: <a href="../../authors.html#Daniel_Vik">Daniel Vik</a><br>
|
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Location: <a href="../../location.html#US">US</a> - <em>United States of America</em> (<em>United States</em>)</li>
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<h2 id="to-build">To build:</h2>
|
||
<pre><code> make</code></pre>
|
||
<h2 id="to-use">To use:</h2>
|
||
<pre><code> ./vik2</code></pre>
|
||
<h2 id="judges-remarks">Judges’ remarks:</h2>
|
||
<p>The fun thing about <a href="https://en.wikipedia.org/wiki/C_preprocessor">CPP</a> abuses
|
||
is that, in most cases, running the
|
||
<a href="https://en.wikipedia.org/wiki/C_preprocessor">preprocessor</a> on them doesn’t
|
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help you decipher the obfuscated code. That’s assuming your preprocessor can
|
||
take it at all.</p>
|
||
<h2 id="authors-remarks">Author’s remarks:</h2>
|
||
<h3 id="introduction">Introduction</h3>
|
||
<p>It’s been a while since the last
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||
<a href="https://en.wikipedia.org/wiki/C_preprocessor">pre-processor</a> killer won the
|
||
IOCCC. I thought it was time to relive hour long compile times so I made a
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||
program that does (almost) all computation in the pre-processor. The program
|
||
even causes <code>gcc</code> (and other pre-processors) to crash when configured to do
|
||
maximum number of computations. The default configuration of the
|
||
<a href="https://github.com/ioccc-src/winner/blob/master/2004/vik2/Makefile">Makefile</a> is set to make the program compile in a not too long time.</p>
|
||
<p>I’ve got <code>cpp</code> to crash in a couple of different ways. Most common is to
|
||
get a segmentation fault, but a couple of times it just got stuck in
|
||
some infinite loop.</p>
|
||
<p>I actually had to write my own
|
||
<a href="https://en.wikipedia.org/wiki/C_preprocessor">pre-processor</a> to verify that the
|
||
program was doing the right thing…</p>
|
||
<p>Since it takes a very long time to compile the program, there is a
|
||
symbol that can be defined to shorten the compile time and avoid
|
||
compiler errors.</p>
|
||
<h3 id="features">Features</h3>
|
||
<p>The program implements an 11-bit
|
||
<a href="https://en.wikipedia.org/wiki/Arithmetic_logic_unit">ALU</a> in the
|
||
<a href="https://en.wikipedia.org/wiki/C_preprocessor">pre-processor</a>. The ALU has two
|
||
<a href="https://en.wikipedia.org/wiki/Processor_register">registers</a>, <code>X</code> and <code>Y</code>, for
|
||
calculations and one status register <code>SR</code>. Each bit in the registers are
|
||
represented by one symbol that are either defined or undefined.</p>
|
||
<p>The ALU has six instructions:</p>
|
||
<ul>
|
||
<li><code>CLR_X</code>
|
||
<ul>
|
||
<li>Clear <a href="https://en.wikipedia.org/wiki/Processor_register">register</a> <code>X</code>.</li>
|
||
</ul></li>
|
||
<li><code>CLR_Y</code>
|
||
<ul>
|
||
<li>Clear <a href="https://en.wikipedia.org/wiki/Processor_register">register</a> <code>Y</code>.</li>
|
||
</ul></li>
|
||
<li><code>ADD</code>
|
||
<ul>
|
||
<li>Calculates <code>X</code> + <code>Y</code> and stores the result in <code>X</code>. If the result
|
||
is larger than 11 bits, the <a href="https://en.wikipedia.org/wiki/Carry_flag">CARRY
|
||
bit</a> in <code>SR</code> is set otherwise
|
||
the <code>CARRY</code> bit is cleared.</li>
|
||
</ul></li>
|
||
<li><code>SUB</code>
|
||
<ul>
|
||
<li>Calculates <code>X</code> - <code>Y</code> and stores the result in <code>X</code>. If <code>Y</code> was larger than
|
||
<code>X</code>, the <a href="https://en.wikipedia.org/wiki/Carry_flag">CARRY bit</a> in <code>SR</code> is
|
||
set otherwise the <code>CARRY</code> bit is cleared.</li>
|
||
</ul></li>
|
||
<li><code>TST</code>
|
||
<ul>
|
||
<li>If <code>X</code> == <code>Y</code> the <code>EQ</code> bit in <code>SR</code> is set, otherwise the <code>EQ</code> bit is
|
||
cleared. If <code>X</code> < <code>Y</code> the <code>LT</code> bit in <code>SR</code> is set, otherwise the <code>LT</code> bit is
|
||
cleared.</li>
|
||
</ul></li>
|
||
<li><code>INC2</code>
|
||
<ul>
|
||
<li>Calculates <code>X</code> + 2 and stores the result in <code>X</code>. The <a href="https://en.wikipedia.org/wiki/Carry_flag">CARRY
|
||
bit</a> is handled as in the <code>ADD</code>
|
||
instruction.</li>
|
||
</ul></li>
|
||
</ul>
|
||
<p>Internally the <a href="https://en.wikipedia.org/wiki/Arithmetic_logic_unit">ALU</a>
|
||
implements a one bit adder with a carry in and carry out. This adder is the core
|
||
of the ALU. The <code>ADD</code> instruction uses the one bit adder to create the 11-bit
|
||
adder. The <code>SUB</code> instruction is implemented by adding <code>~Y</code> to <code>X</code> and then add 1.
|
||
Finally the <code>TST</code> instruction calculates <code>X-Y</code> and checks the result and the
|
||
<a href="https://en.wikipedia.org/wiki/Carry_flag">CARRY bit</a> in the <code>SR</code>
|
||
<a href="https://en.wikipedia.org/wiki/Processor_register">register</a> to set the <code>EQ</code> and
|
||
<code>LT</code> bits.</p>
|
||
<p>All calculations are made using only <code>#ifdef</code>, <code>#ifndef</code>, <code>#else</code>, <code>#endif</code>,
|
||
<code>#define</code> and <code>#undef</code>. I never assign a value to a defined symbol. The
|
||
logic is done by assuming that a defined symbol is 1 and an undefined
|
||
symbol is 0. (I guess this means that I have unlimited memory as long as
|
||
I only store zeroes (!)).</p>
|
||
<p>The application that uses the
|
||
<a href="https://en.wikipedia.org/wiki/C_preprocessor">pre-processor</a>
|
||
<a href="https://en.wikipedia.org/wiki/Arithmetic_logic_unit">ALU</a> is a <a href="https://en.wikipedia.org/wiki/Prime_number">prime
|
||
number</a>
|
||
generator. The application uses the same pre-processor directives.
|
||
Needed variables are stored in memory represented by one defined or
|
||
undefined symbol per bit. When doing arithmetics, the variables are
|
||
loaded into the <code>X</code> and <code>Y</code> registers by defining / undefining the <code>X</code> and <code>Y</code>
|
||
<a href="https://en.wikipedia.org/wiki/Processor_register">register</a> bits. Then the
|
||
calculation is made and the result is moved back to the memory.</p>
|
||
<p>The choice of application may be a bit unfortunate since we’ve already
|
||
seen a winning entry calculating <a href="https://en.wikipedia.org/wiki/Prime_number">prime
|
||
numbers</a> in the
|
||
<a href="https://en.wikipedia.org/wiki/C_preprocessor">pre-processor</a>.
|
||
There is a big difference though. The
|
||
<a href="../../1988/applin/index.html">1988/applin</a> entry uses pre-processor arithmetic
|
||
(in a very nice way though). This program only defines and undefines symbols in
|
||
a well defined ;) way and doesn’t do any pre-processor arithmetics.</p>
|
||
<p>The reason why I chose to do a <a href="https://en.wikipedia.org/wiki/Prime_number">prime
|
||
number</a> application is that the
|
||
algorithm can be written to do a lot of calculations without a lot of nesting
|
||
(GNU <code>cpp</code> allows only 200 nested includes).</p>
|
||
<h3 id="build-and-run">Build and Run</h3>
|
||
<p>First, do a first pre-processing of the initial definitions. The <code>FNAME</code>
|
||
symbol must be defined to the name of the output file. If you want to
|
||
speed up the compilation, define the <code>STOP</code> symbol to anything from <code>_3</code> to
|
||
<code>_10</code>. (The default value is <code>_10</code> which will make the compilation take some
|
||
time.) Prime numbers up to <code>2^STOP</code> will be calculated.</p>
|
||
<pre><code> cpp '-DSTOP=_5' '-DFNAME="tmp1.c"' prog.c tmp1.c</code></pre>
|
||
<p>Then use <code>cpp</code> or any other
|
||
<a href="https://en.wikipedia.org/wiki/C_preprocessor">pre-processor</a> to do the actual
|
||
work. This will take some time….</p>
|
||
<pre><code> cpp tmp1.c > tmp2.c</code></pre>
|
||
<p>Finally compile the pre-processed file</p>
|
||
<pre><code> cc -O tmp2.c -o prog</code></pre>
|
||
<p>Then run the program to reveal all prime numbers up to 32 (if you used
|
||
<code>STOP=_5</code> as above):</p>
|
||
<pre><code> ./vik2</code></pre>
|
||
<h3 id="verification">Verification</h3>
|
||
<p>I wasn’t able to compile the full program which calculates <a href="https://en.wikipedia.org/wiki/Prime_number">prime
|
||
numbers</a> up to 1024 using GNU <code>cpp</code>
|
||
(or any other <a href="https://en.wikipedia.org/wiki/C_preprocessor">pre-processor</a> tool) so
|
||
I had to write my own. Knowing how the program works it was quite easy to reduce
|
||
the compilation time from several hours to about one second. I also added some
|
||
statistics to my home made pre-processor and I found that calculating prime
|
||
numbers up to 1024 makes the program include itself over 6.8 million times (see
|
||
the statistics table below).</p>
|
||
<h3 id="obfuscation">Obfuscation</h3>
|
||
<p>Well, since 98.5% of the program is
|
||
<a href="https://en.wikipedia.org/wiki/C_preprocessor">preprocessor</a> directives, the
|
||
main obfuscation is the use of preprocessor directives.</p>
|
||
<p>Doing arithmetics without actually using any arithmetic operations makes
|
||
the program quite hard to follow.</p>
|
||
<p>In order to actually do the calculations, the program includes itself a
|
||
lot.</p>
|
||
<p>The symbol names are made as short as possible to meet the space limits.
|
||
This of course adds to the obfuscation (even though the program is
|
||
quite obfuscated with longer, readable macro names.</p>
|
||
<p>Finally, I made the 1.5% C code a bit harder to read by breaking all
|
||
lines after three characters.</p>
|
||
<p>The program has 1029 lines which makes it the longest entry (so far).</p>
|
||
<p>Even though the pre-processed and indented output is easier to read, it
|
||
is quite hard to find the code in it. The size of the pre-processed file
|
||
is several Mb when using GNU <code>cpp</code>.</p>
|
||
<h3 id="limitations">Limitations</h3>
|
||
<p>In order to fit the program within the space limits, I had to define the
|
||
<code>#define</code>, <code>#endif</code>, and some other directives as single character symbols.
|
||
This does not compile on all
|
||
<a href="https://en.wikipedia.org/wiki/C_preprocessor">pre-processors</a> but using GNU
|
||
<code>cpp</code> as a first compilation step solves this.</p>
|
||
<h3 id="statistics">Statistics</h3>
|
||
<p>The table below contains some interesting statistics about the compilation of
|
||
the program. The intermediate file size is the size of the output file of the
|
||
<code>cpp</code> <a href="https://en.wikipedia.org/wiki/C_preprocessor">pre-processor</a>. The times
|
||
taken to pre-process the program were measured using GNU <code>cpp</code> on my 2.0MHz P4
|
||
with 512Mb ram and a lot of disk.</p>
|
||
<pre><code> Generated Recursive Max nest Intermediate
|
||
Level prime nrs includes count file size Time
|
||
|
||
_3 < 8 2 322 9 74 748 4"
|
||
_4 < 16 4 672 9 182 652 9"
|
||
_5 < 32 14 237 9 629 121 32"
|
||
_6 < 64 43 748 9 1 998 134 1'41"
|
||
_7 < 128 149 851 11 6 823 575 5'50"
|
||
_8 < 256 526 874 17 24 028 933 20'37"
|
||
_9 < 512 1 920 272 38 65 527 808(*) 1h 42'19"(*)
|
||
_10 < 1024 6 826 389 114 63 782 912(*) 2h 47'58"(*)
|
||
|
||
(*) Before cpp crashed.</code></pre>
|
||
<!--
|
||
|
||
Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.
|
||
|
||
You are free to share and adapt this file under the terms of this license:
|
||
|
||
Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
|
||
|
||
For more information, see:
|
||
|
||
https://creativecommons.org/licenses/by-sa/4.0/
|
||
|
||
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|
||
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|
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|
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|
||
|
||
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|
||
|
||
<div id="inventory">
|
||
<h1 id="inventory-for-2004vik2">Inventory for 2004/vik2</h1>
|
||
</div>
|
||
<h2 id="primary-files">Primary files</h2>
|
||
<ul>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2004/vik2/vik2.c">vik2.c</a> - entry source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2004/vik2/Makefile">Makefile</a> - entry Makefile</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2004/vik2/vik2.orig.c">vik2.orig.c</a> - original source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2004/vik2/vik2_1.c">vik2_1.c</a> - include file for entry source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2004/vik2/vik2.possible.cat.death.c">vik2.possible.cat.death.c</a> - special source file for special make rule</li>
|
||
</ul>
|
||
<h2 id="secondary-files">Secondary files</h2>
|
||
<ul>
|
||
<li><a href="2004_vik2.tar.bz2">2004_vik2.tar.bz2</a> - download entry tarball</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2004/vik2/README.md">README.md</a> - markdown source for this web page</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2004/vik2/.entry.json">.entry.json</a> - entry summary and manifest in JSON</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2004/vik2/.gitignore">.gitignore</a> - list of files that should not be committed under git</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2004/vik2/.path">.path</a> - directory path from top level directory</li>
|
||
<li><a href="index.html">index.html</a> - this web page</li>
|
||
</ul>
|
||
<hr style="width:10%;text-align:left;margin-left:0">
|
||
<h4>
|
||
Jump to: <a href="#">top</a>
|
||
</h4>
|
||
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|
||
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|
||
|
||
</div>
|
||
|
||
<!-- END: this line ends content from: inc/after-content.default.html -->
|
||
<!-- START: this line starts content from: inc/footer.inventory.html -->
|
||
|
||
<!--
|
||
|
||
Copyright © 1984-2025 by Landon Curt Noll. All Rights Reserved.
|
||
|
||
You are free to share and adapt this file under the terms of this license:
|
||
|
||
Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
|
||
|
||
For more information, see:
|
||
|
||
https://creativecommons.org/licenses/by-sa/4.0/
|
||
|
||
-->
|
||
|
||
<div class="footer">
|
||
|
||
<div id="copyright"><h3>Copyright © 1984-2025 by Landon Curt Noll:
|
||
<a href="https://creativecommons.org/faq/#what-does-some-rights-reserved-mean"
|
||
target="_blank"
|
||
rel="license noopener noreferrer">Some Rights Reserved</a></h3>
|
||
<p>
|
||
This work is <b>licensed by Landon Curt Noll</b> under
|
||
<b><a href="https://creativecommons.org/licenses/by-sa/4.0/?ref=chooser-v1"
|
||
target="_blank"
|
||
rel="license noopener noreferrer"
|
||
style="display:inline-block;">CC BY-SA 4.0</a></b>.
|
||
<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
|
||
src="../../png/cc.png"
|
||
alt="cc inside circle symbol">
|
||
<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
|
||
src="../../png/by.png"
|
||
alt="person inside circle symbol">
|
||
<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
|
||
src="../../png/sa.png"
|
||
alt="arrow looping back on itself inside circle symbol"><br>
|
||
You should <b>carefully review</b> the
|
||
<b><a href="https://creativecommons.org/licenses/by-sa/4.0/legalcode.en"
|
||
target="_blank"
|
||
rel="license noopener noreferrer">CC BY-SA 4.0 LEGAL CODE</a></b>
|
||
before using the licensed material.<br>
|
||
You may wish to review the
|
||
<b><a href="../../license.html"
|
||
target="_blank"
|
||
rel="license noopener noreferrer">highlights of some of the key features and terms</a></b>
|
||
of <b>CC BY-SA 4.0</b>.<br>
|
||
</p>
|
||
</div>
|
||
|
||
<div id="coda"><h3>Coda</h3>
|
||
<p>
|
||
<a href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fwww.ioccc.org%2F2004%2Fvik2%2Findex.html" rel="nofollow">Nu HTML check this web page</a><br>
|
||
<a href="#top">Jump to top</a> <a href="#content">Jump to Content</a> <a href="#inventory">Jump to Inventory</a><br>
|
||
</p>
|
||
</div>
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</div>
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</body>
|
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</html>
|
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