Landon Curt Noll
cc73503c10
We add to the top level Makefile, some initial rules that
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311 lines
15 KiB
HTML
311 lines
15 KiB
HTML
<!DOCTYPE html>
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<!-- START: two lines up starts content from: inc/top.default.html -->
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<!-- -->
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<!-- !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! -->
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<head>
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<link rel="stylesheet" href="../../ioccc.css">
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<meta charset="utf-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
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<title>1989/paul - Most complex algorithm</title>
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<meta name="description" content="1989 IOCCC entry paul - Most complex algorithm">
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<meta name="keywords" content="IOCCC, 1989, IOCCC 1989, IOCCC entry, paul, Most complex algorithm">
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<div class="header">
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<img src="../../png/ioccc.png" alt="IOCCC image by Matt Zucker" width=300 height=110>
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<h1>The International Obfuscated C Code Contest</h1>
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<h2>1989/paul - Most complex algorithm</h2>
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<div class="topnav">
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<a class="Left" href="../ovdluhe/index.html">← ovdluhe</a>
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<a class="Left" href="../index.html">↑ 1989 ↑</a>
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<a class="Left" href="../robison/index.html">robison →</a>
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<a class="Right" href="#inventory">Inventory</a>
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<div class="sidenav">
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<a href="#content">Jump to contents</a>
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</div>
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<hr>
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<div class="sidenav">
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<a href="../../index.html">IOCCC Home</a>
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<a href="../../years.html">Winning Entries</a>
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<a href="../../winners.html">People who have won</a>
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</div>
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<hr>
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<div class="sidenav">
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<a href="../../news.html">IOCCC News</a>
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<a href="../../faq.html#submit">How to enter the IOCCC</a>
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<a href="../../faq.html">FAQ</a>
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</div>
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<hr>
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<div class="sidenav">
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<a href="../../bugs.html">Bugs & (mis)features</a>
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<a href="../../faq.html#fix_a_winner">Fixing IOCCC winners</a>
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<a href="../../faq.html#fix_web_site">Fixing the web site</a>
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<a href="../../faq.html#fix_author">Fixing winner info</a>
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<a href="../../thanks-for-help.html">Thanks for the help</a>
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</div>
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<hr>
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<div class="sidenav">
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<a href="../../judges.html">The IOCCC Judges</a>
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<a href="../../contact.html">Contacting the IOCCC</a>
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</div>
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<hr>
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<div class="sidenav">
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<a href="#top">Jump to top</a>
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<a name="content"></a>
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<h2 id="author"><a name="author"></a>Author:</h2>
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<ul>
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<li>Name: <a href="../../authors.html#Paul_E_Black">Paul E.
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Black</a><br> Location: <a href="../../location.html#US">US</a>
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<br><br></li>
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</ul>
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<h2 id="to-build">To build:</h2>
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<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="fu">make</span> all</span></code></pre></div>
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<p>There is an alternate version with a trace routine that the author
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had commented out. See <a href="#alternate-code">alternate code</a>
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below for more details.</p>
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<h2 id="try">Try:</h2>
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<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="ex">./paul</span></span></code></pre></div>
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<h2 id="alternate-code">Alternate code:</h2>
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<p>This version was described by the author like:</p>
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<blockquote>
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<p>I could have squeezed the program under 1024 bytes without the trace
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subroutine, but I felt it was important for understanding the program.
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Besides it is fun to watch the tape zooming back and forth as the
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program runs. A much better debugger or trace could easily be added.</p>
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</blockquote>
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<h3 id="alternate-build">Alternate build:</h3>
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<div class="sourceCode" id="cb3"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="fu">make</span> alt</span></code></pre></div>
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<h3 id="alternate-use">Alternate use:</h3>
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<div class="sourceCode" id="cb4"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="ex">./paul.alt</span></span></code></pre></div>
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<h2 id="judges-remarks">Judges’ remarks:</h2>
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<p>The author’s comments is a detailed program explanation and spoiler.
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If you want a real challenge, don’t read any further and try to
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understand the program via the source.</p>
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<h3 id="historical-note">Historical note:</h3>
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<p>The original source contained a long line which caused many mailers
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to barf. The original file may be re-constructed by removing the
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trailing <code>\</code> on line 12 and joining lines 12 and 13 together
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without a space.</p>
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<p>However as this is no longer a problem the trailing <code>\</code>
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has been restored in all versions, both the original and the fixed for
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modern systems version.</p>
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<h2 id="authors-remarks">Author’s remarks:</h2>
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<p>This programs computes and prints Fibonacci numbers by simulating a
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Turing machine with the proper program. Understanding the C program,
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i.e., a Turing machine simulator, is only the first and simplest step.
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The Turing machine program must be understood, too! (it is trivial,
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perhaps even natural to write incredibly obscure Turing programs.)</p>
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<p>If the program is invoked with an operand, the operand is used as the
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Turing program. It includes a “trace” facility, subroutine
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<code>r</code> (commented out for obscurity), to help write and debug
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Turing programs. Just the thing for some fun in a Theory of Computation
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class.</p>
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<p>The Turing machine tape is represented as a doubly linked list of
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pointers. The forward and backward links are <code>XOR</code>ed together
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and stored in one pointer. If we always keep one of the links on hand,
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we can recover the other link at any time. The variable <code>q</code>
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is the scan head (and a pointer at some tape cell), and <code>p</code>
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is a “previous” link. The state of the tape is stored in the low order
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bit of the pointer. Since we always allocate an even number of bytes,
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the low order bit carries no information (see <a
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href="#portability">portability</a> below.) Memory representing a tape
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cell is allocated when the cell is first scanned. Thus the simulation
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begins with a tape effectively the size of virtual memory set to all
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zeros. Since a header can be added to any Turing program to write
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initial data and position the scan head, this is little loss of
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generality.</p>
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<p>The simulated Turing machine has a single tape with either a
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<code>1</code> or a <code>0</code> in each cell. The Turing machine
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language format is a string of three bytes. The first byte is the
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current state. The second byte is the next state. (The last bit of
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states is ignored, i.e., <code>B</code> and <code>C</code> are the same
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state, in an attempt to be able to have interesting words in the
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program.) The third byte is composed of bits. Bit <code>1</code>
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(<code>2&byte</code>) is the symbol scanned, i.e. an instruction is
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selected for state and for a match with the symbol under the scan head.
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Bit <code>2</code> (<code>4&byte</code>) is the new symbol to be
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written to the cell. Bit <code>3</code> (<code>8&byte</code>) is the
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direction to move the scan head: <code>0</code> for left and
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<code>1</code> for right. If bit <code>4</code>
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(<code>16&byte</code>) is true, the next character is sent to
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<code>stdout</code>. (I added this feature so programs could print
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results.)</p>
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<p>The Turing machine has next state <code>j</code> when it begins. The
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cycle is (1) exit if the state is <code>x</code>, (2) find the next
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instruction (given the state and the character under the scan head).
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(The program string is searched forward for the next matching
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instruction. If the end of the string is reached, the search begins
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again at the first of the string. Thus states can be used as local
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labels in different places.) (3) change to the next state, (4) print a
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character if indicated, (5) write the tape symbol, and (6) move the scan
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head. The cycle then repeats with step 1. A call to the trace routine is
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just before step 2, but is commented out.</p>
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<h3 id="quick-outline-of-the-turing-program">Quick outline of the Turing
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program:</h3>
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<p>The previous and current Fibonacci numbers are kept in base 1 form
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with the current on the right. The first three steps set up the first
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two numbers, <code>1</code> and <code>1</code>. Then [beginning with
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<code>@ (</code>] a marker of <code>III</code> is created and the
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current number is copied to the right of the marker. Then (beginning
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with <code>OV</code>) the number is converted to binary by repeatedly
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dividing by 2 leaving I for remainder <code>1</code>, and II for
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remainder <code>0</code>. Next (beginning with <code>WV</code>) the
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binary representation is printed and its symbols and the marker are
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erased. Finally (beginning with <code>EEn</code>) the two numbers are
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added and the current number copied to the left to become the previous.
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Then the cycle repeats.</p>
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<h3 id="portability">Portability</h3>
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<p>The program requires that the lowest bit of a pointer to be 0.</p>
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<p>I could have squeezed the program under 1024 bytes without the trace
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subroutine, but I felt it was important for understanding the program.
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Besides it is fun to watch the tape zooming back and forth as the
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program runs. A much better debugger or trace could easily be added.</p>
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<h2 id="copyright-and-cc-by-sa-4.0-license">Copyright and CC BY-SA 4.0
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License:</h2>
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<p>This file is Copyright (c) 2023 by Landon Curt Noll. All Rights
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Reserved. You are free to share and adapt this file under the terms of
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this license:</p>
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<pre><code>Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)</code></pre>
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<p>For more information, see:
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https://creativecommons.org/licenses/by-sa/4.0/</p>
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<h1 id="inventory-for-1989paul"><a name="inventory"></a>Inventory for
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1989/paul</h1>
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<h2 id="primary-files">Primary files</h2>
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<ul>
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<li><a href="index.html">index.html</a> - entry home page</li>
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<li><a
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href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/paul.c">paul.c</a>
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- winning source</li>
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<li><a
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href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/Makefile">Makefile</a>
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- entry Makefile</li>
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<li><a
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href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/paul.alt.c">paul.alt.c</a>
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- alternative source</li>
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<li><a
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href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/paul.orig.c">paul.orig.c</a>
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- original source</li>
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<li><a href="1989_paul.tar.bz2">1989_paul.tar.bz2</a> - download winning
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source</li>
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</ul>
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<h2 id="secondary-files">Secondary files</h2>
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<ul>
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<li><a
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href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/.entry.json">.entry.json</a>
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- description of entry in JSON</li>
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<li><a
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href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/.gitignore">.gitignore</a>
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- list of files that should not be committed under git</li>
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<li><a href=".path">.path</a> - directory path from top directory</li>
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<li><a
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href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/README.md">README.md</a>
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- markdown source for index.html</li>
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</ul>
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<div class="footer">
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<hr>
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<h2>Coda</h2>
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<p><a href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fioccc-src.github.io%2Ftemp-test-ioccc%2F1989%2Fpaul%2Findex.html">Nu HTML check this web page</a></p>
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<p><a href="#top">Jump to top</a> <a href="#content">Jump to Content</a> <a href="#inventory">Jump to Inventory</a></p>
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</div>
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</body>
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</html>
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