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ioccc/1991/dds/index.html
T
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>1991/dds - Most well rounded</h2>
<h3>basic compiler that is heavily compressed</h3>
</div>
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<div class="navbar">
<a class="Left" href="../davidguy/index.html">&larr; 1991/davidguy</a>
<a class="Left" href="../index.html">&uarr; 1991 &uarr;</a>
<a class="Left" href="../fine/index.html">1991/fine &rarr;</a>
<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/1991/dds/dds.c">C code</a>
<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/1991/dds/Makefile">Makefile</a>
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<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/1991/dds/dds.orig.c">Original C</a>
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<h2 id="author">Author:</h2>
<ul>
<li>Name: <a href="../../authors.html#Diomidis_Spinellis">Diomidis Spinellis</a><br>
Location: <a href="../../location.html#GR">GR</a> - <em>Hellenic Republic</em> (<em>Greece</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> ./dds basic_program
./a.out 2&gt;/dev/null</code></pre>
<h2 id="try">Try:</h2>
<p>The author suggests trying:</p>
<pre><code> ./dds LANDER.BAS
./a.out</code></pre>
<p>Notice that a file <code>a.c</code> has been generated. Can you tell how <code>a.c</code> was
produced? How does <code>a.c</code> relate to <a href="https://github.com/ioccc-src/winner/blob/master/1991/dds/LANDER.BAS">LANDER.BAS</a>?</p>
<p>What happens if you give the program a C program like itself? Try:</p>
<pre><code> ./dds dds.c</code></pre>
<p>You’ll get errors yes but what does the generated file look like? What about
other types of files?</p>
<h2 id="judges-remarks">Judges’ remarks:</h2>
<p>This obfuscated program translates BASIC programs into obfuscated
C programs by way of an obfuscated algorithm.</p>
<h2 id="authors-remarks">Author’s remarks:</h2>
<p>This program is a companion to the <a href="../../1990/dds/index.html">1990/dds</a>
1990 DDS-BASIC interpreter program. This compiles BASIC programs into compilable C code
and then compiles it. The input format is almost identical to the input format
of the DDS-BASIC interpreter. The program needs an executable C compiler called
<code>cc</code> in your path in order to work.</p>
<h3 id="program-commands">Program commands:</h3>
<ul>
<li>variable names A to Z</li>
<li>FOR var = exp TO exp</li>
<li>GOSUB exp</li>
<li>GOTO exp</li>
<li>INPUT variable</li>
<li>PRINT exp</li>
<li>REM any text</li>
<li>variables initialized to 0 on RUN</li>
<li>NEXT variable</li>
<li>RETURN</li>
<li>IF exp THEN exp</li>
<li>PRINT string</li>
<li>var = exp</li>
<li>END</li>
</ul>
<p>Expressions are the same as the expressions of the C language.
Many system calls and C library calls can be used.</p>
<h3 id="input-format">Input format:</h3>
<ul>
<li>Free format positioning of tokens on the line.</li>
<li>No space is allowed before the line number.</li>
<li>Exactly one space is needed after the <code>FOR</code> and <code>NEXT</code> tokens.</li>
<li>ALL INPUT MUST BE UPPERCASE.</li>
</ul>
<h3 id="error-checking-error-reports">Error checking / error reports:</h3>
<p>The compiler silently ignores many errors.
Other errors may produce errors in later phases of the compilation.</p>
<h3 id="can-you-figure-out-how-the-compiler-works">Can you figure out how the compiler works?</h3>
<h4 id="hint">Hint:</h4>
<p>The compiler is NOT written in C, so this is really a meta-obfuscated
program. The C code is an interpreter for the four register, seven
instruction <code>COGNIMP$</code> machine that is contained in the <code>s</code> string.
(<code>COGNIMP$</code> is named after the symbolic names of the seven instructions it
defines (<code>Copy</code>, <code>Output</code>, <code>Goto</code>, <code>iNcrement</code>, <code>If</code>, <code>Match</code> and <code>Print</code>).</p>
<p>The <code>$</code> sign is used for labels. The actual compiler is written in <code>COGNIMP$</code>.
Browsing through the <code>COGNIMP$</code> code we encourage you to examine the loops for
scanning the expression in the <code>IF</code> statement and the way a decision tree is
implemented in order to match the statements. (Of course the <code>s</code> string is
encoded by adding one to every character of it just to confuse you).</p>
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<div id="inventory">
<h1 id="inventory-for-1991dds">Inventory for 1991/dds</h1>
</div>
<h2 id="primary-files">Primary files</h2>
<ul>
<li><a href="https://github.com/ioccc-src/winner/blob/master/1991/dds/dds.c">dds.c</a> - entry source code</li>
<li><a href="https://github.com/ioccc-src/winner/blob/master/1991/dds/Makefile">Makefile</a> - entry Makefile</li>
<li><a href="https://github.com/ioccc-src/winner/blob/master/1991/dds/dds.orig.c">dds.orig.c</a> - original source code</li>
<li><a href="https://github.com/ioccc-src/winner/blob/master/1991/dds/LANDER.BAS">LANDER.BAS</a> - BASIC source code for Lunar Lander game</li>
</ul>
<h2 id="secondary-files">Secondary files</h2>
<ul>
<li><a href="1991_dds.tar.bz2">1991_dds.tar.bz2</a> - download entry tarball</li>
<li><a href="https://github.com/ioccc-src/winner/blob/master/1991/dds/README.md">README.md</a> - markdown source for this web page</li>
<li><a href="https://github.com/ioccc-src/winner/blob/master/1991/dds/.entry.json">.entry.json</a> - entry summary and manifest in JSON</li>
<li><a href="https://github.com/ioccc-src/winner/blob/master/1991/dds/.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/1991/dds/.path">.path</a> - directory path from top level directory</li>
<li><a href="index.html">index.html</a> - this web page</li>
</ul>
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