Files
Landon Curt Noll a1c86c8a7a add original C links to entry navigation bars
The navigation bar for a winning entry now has a "_Original C_" link
(between the ✅ and the Inventory on the right hand side) so that one
may easily view the original C code that was submitted for IOCCC judging.

Ran `make www timestamp` to perform the above.
2025-08-10 12:46:23 -07:00

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<h1>The International Obfuscated C Code Contest</h1>
<h2>1995/vanschnitz - Worst abuse of the C preprocessor and most likely to amaze</h2>
<h3>Towers of Hanoi via the C pre-processor</h3>
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<div class="navbar">
<a class="Left" href="../spinellis/index.html">&larr; 1995/spinellis</a>
<a class="Left" href="../index.html">&uarr; 1995 &uarr;</a>
<a class="Left" href="../../1996/august/index.html">1996/august &rarr;</a>
<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/1995/vanschnitz/vanschnitz.c">C code</a>
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<h2 id="authors">Authors:</h2>
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<ul>
<li>Name: <a href="../../authors.html#David_Van_Brackle">David Van Brackle</a><br>
Location: <a href="../../location.html#US">US</a> - <em>United States of America</em> (<em>United States</em>)
<br><br></li>
<li>Name: <a href="../../authors.html#Mark_Schnitzius">Mark Schnitzius</a><br>
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 all</code></pre>
<p>The authors provided an unobfuscated version, originally uuencoded but uudecoded by us
in 2023. See <a href="#alternate-code">Alternate code</a> below.</p>
<h3 id="bugs-and-misfeatures">Bugs and (Mis)features:</h3>
<p>The current status of this entry is:</p>
<blockquote>
<p><strong>STATUS: missing file - please provide it</strong></p>
</blockquote>
<p>For more detailed information see <a href="../../bugs.html#1995_vanschnitz">1995/vanschnitz in bugs.html</a>.</p>
<h2 id="to-use">To use:</h2>
<pre><code> ./vanschnitz</code></pre>
<h2 id="try">Try:</h2>
<pre><code> ./try.sh</code></pre>
<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 without looking at the Alternate code.</p>
<p>If you get stuck, come back and look at the Alternate code.</p>
<h2 id="alternate-code">Alternate code:</h2>
<p>The authors provided unobfuscated version of the program. Originally uuencoded
we have decoded it for the wider audience in
<a href="https://github.com/ioccc-src/winner/blob/master/1995/vanschnitz/vanschnitz.alt.c">vanschnitz.alt.c</a>.</p>
<p>They encourage you to first try and figure out the program without reading the
deobfuscated version.</p>
<h3 id="alternate-build">Alternate build:</h3>
<pre><code> make alt</code></pre>
<h3 id="alternate-use">Alternate use:</h3>
<p>Use <code>vanschnitz.alt</code> as you would <code>vanschnitz</code> above.</p>
<h2 id="judges-remarks">Judges’ remarks:</h2>
<p>Back in 1995, values of <code>LEVEL&gt;8</code> caused some compilers (and in one case a
system) to crash during compilation. In 2023 with modern systems this is not
really a problem.</p>
<p>Back in 1995 we also suggested that for a bad/slow time to try <code>LEVEL=15</code> but
this is not a big deal in 2023 either.</p>
<h2 id="authors-remarks">Authors’ remarks:</h2>
<p>A classic problem in computer science is known as the Towers
of Hanoi. It involves a set of different-sized disks mounted
on one of three pegs. The object is to move the pile of disks
to one of the other pegs. You may only move one disk at a
time, and there is an additional constraint that a disk may
never be placed on top of a smaller disk.</p>
<p>Our program solves the Towers of Hanoi problem. Well, that’s
not exactly true; actually, it’s the compiler that solves the
problem. The resulting program just prints out the correct
solution.</p>
<p>How do you trick a compiler into actually solving the problem?
First, you must tell it how many disks you wish to solve it
for. This is done by defining the symbol <code>n</code> on the compile
line. For instance, to cause the compiler to solve the Towers
of Hanoi problem with four disks, you would compile the program
like this:</p>
<pre><code> gcc hanoi.c -o hanoi -Dn=4</code></pre>
<p>A default value of <code>5</code> will be used for <code>n</code> if you do not define
it on the command line. The value of <code>n</code> cannot be greater than
fifteen (the compiler we used to test has a limit on the <code>#include</code>
depth). The compiler then solves the problem using binary
arithmetic based on whether particular symbols are defined or not.</p>
<p>To loop, the program <code>#include</code>s itself. This is, of course, expensive; one
compile we did with <code>n=14</code> took about fifty minutes to compile on our system
(compiling with <code>n=15</code> caused our system to crash).</p>
<p>The resulting program that the compiler generates simply
prints out the answer. Did I say “simply”? Actually, the
whole resulting program consists of a single <code>printf(3)</code> statement,
consisting of a massive string constant of length <code>35*(2^n-1)</code>,
followed by <code>3*(2^n-1)</code> integers which get formatted into the
string. For our <code>n=14</code> run, this adds up to a string constant
of length 573405, followed by 49149 integers delimited by
commas. (Generating the string constant depends on the
ANSI C feature in which adjacent character strings are
concatenated; a version that does not use this feature has been
included for people who can only run K&amp;R). A good way to see
the resulting program (on a Unix system) is to do the command</p>
<pre><code> gcc hanoi.c -E -Dn=5 | grep -v \# | grep -v ^\$</code></pre>
<p>For an odd number of disks, the program will provide a
solution wherein the disks end up on peg 2; for an even
number of disks, they will end on peg 3. This should
provide some hint as to what sort of algorithm is used.</p>
<p>We have included a <a href="https://github.com/ioccc-src/winner/blob/master/1995/vanschnitz/vanschnitz.alt.c">deobfuscated version</a> of the program, with
meaningful symbol names and comments, but we encourage you
to try to decipher the program without it…</p>
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<h1 id="inventory-for-1995vanschnitz">Inventory for 1995/vanschnitz</h1>
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<h2 id="primary-files">Primary files</h2>
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<li><a href="https://github.com/ioccc-src/winner/blob/master/1995/vanschnitz/vanschnitz.c">vanschnitz.c</a> - entry source code</li>
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