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>1990/dg - Best abuse of the C preprocessor</h2>
<h3>rot13 done with strange cpp macros</h3>
</div>
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<div class="navbar">
<a class="Left" href="../dds/index.html">&larr; 1990/dds</a>
<a class="Left" href="../index.html">&uarr; 1990 &uarr;</a>
<a class="Left" href="../jaw/index.html">1990/jaw &rarr;</a>
<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/1990/dg/dg.c">C code</a>
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<h2 id="author">Author:</h2>
<ul>
<li>Name: <a href="../../authors.html#David_Goodenough">David Goodenough</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>
<h2 id="to-use">To use:</h2>
<pre><code> echo foo bar | ./dg</code></pre>
<h2 id="try">Try:</h2>
<pre><code> ./try.sh</code></pre>
<h2 id="judges-remarks">Judges’ remarks:</h2>
<p>Some C preprocessors got confused about single quotes in certain cases.
In particular, the following source line:</p>
<pre><code> b12(ase(bco(acp(bi(acp(bcp(acp(bpl(aqu(bqu(A))))))))))))))))))))))))))))))</code></pre>
<p>sometimes has to be changed to:</p>
<pre><code> b12(ase(bco(acp(bi(acp(bcp(acp(bpl(&#39;A&#39;))))))))))))))))))))))))))))</code></pre>
<p>particularly if the C preprocessor botches single quotes in cpp expansions,
which we have done for the wider audience.</p>
<h2 id="authors-remarks">Author’s remarks:</h2>
<p>If my preprocessor could hack it, I could write this as one single line rather
than 4, but when I do that I get a complaint “defines nested too deeply”.</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>This is another rot13 job (believe it or not) - the <code>#define</code>s are a
novel way of adding tokens: <code>#define b12(x) 12 x</code> means that at
some point in the source a <code>12</code> is followed by the compressed nested
<code>#define</code>s. The <code>b12</code> gets the previous compression as an argument, and
prepends the <code>12</code>, thus making another step in the recreation of the
source. The <code>axx()</code> <code>#define</code>s do the same, but add tokens after.</p>
<p>As for the rot13 algorithm, it relies on <code>index(3)</code> to find if the
character is in the set <code>A-Za-z</code>. <code>l[]</code> is an array that gets filled
with:</p>
<pre><code> &quot;nopqrstuvwxyzzzzabcdefghijklmmmmNOPQRSTUVWXYZZZZABCDEFGHIJKLMMMM&quot;</code></pre>
<p>If <code>index(3)</code> says the char is in the alphabet, then XOR the offset
with <code>16</code> to translate, and output, otherwise pass it unchanged.</p>
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<div id="inventory">
<h1 id="inventory-for-1990dg">Inventory for 1990/dg</h1>
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<h2 id="primary-files">Primary files</h2>
<ul>
<li><a href="https://github.com/ioccc-src/winner/blob/master/1990/dg/dg.c">dg.c</a> - entry source code</li>
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<li><a href="1990_dg.tar.bz2">1990_dg.tar.bz2</a> - download entry tarball</li>
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<li><a href="https://github.com/ioccc-src/winner/blob/master/1990/dg/.entry.json">.entry.json</a> - entry summary and manifest in JSON</li>
<li><a href="https://github.com/ioccc-src/winner/blob/master/1990/dg/.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/1990/dg/.path">.path</a> - directory path from top level directory</li>
<li><a href="index.html">index.html</a> - this web page</li>
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