Landon Curt Noll
c457b16358
Renamed `ioccc.ico` to `favicon.ico`. Correctly added use of `favicon.ico` to all constructed HTML headers. Fixed the smart quote in HTML elements problem. Moved HTML "DO NOT EDIT" comments down below at the bottom of the HTML phase 1 section. According to to the Nu Html Checker, a charset attribute on a meta element found after the first 1024 bytes. Changed `bin/md2html.sh` VERSION from "1.1.3 2024-03-28" to "1.2 2024-03-30". Improved `bin/gen-status.sh` to adjust the "status_update" value only when the "contest_status" is changed. Performed a `make www` to perform and test the above under macOS.
336 lines
17 KiB
HTML
336 lines
17 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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<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>
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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="https://github.com/ioccc-src/temp-test-ioccc/1989/paul/paul.c">C code</a>
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<a class="Right" href="https://github.com/ioccc-src/temp-test-ioccc/1989/paul/Makefile">Makefile</a>
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<a class="Right" href="#inventory">Inventory</a>
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<a href="#content">Jump to contents</a>
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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="../../authors.html">People who have won</a>
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<a href="../../location.html">Location of authors</a>
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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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<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_an_entry">Fixing IOCCC entries</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 author 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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<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. Black</a><br>
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Location: <a href="../../location.html#US">US</a> - <em>United States of America</em> (<em>United States</em>)
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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 had commented
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out. See <a href="#alternate-code">alternate code</a> 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
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trace subroutine, but I felt it was important for understanding
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the program. Besides it is fun to watch the tape zooming back
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and forth as the program runs. A much better debugger or trace
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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. If you
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want a real challenge, don’t read any further and try to understand the program
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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 to barf.
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The original file may be re-constructed by removing the trailing <code>\</code> on line 12
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and joining lines 12 and 13 together without a space.</p>
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<p>However as this is no longer a problem the trailing <code>\</code> has been restored in all
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versions, both the original and the fixed for 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
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simulating a Turing machine with the proper program.
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Understanding the C program, i.e., a Turing machine simulator,
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is only the first and simplest step. The Turing machine
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program must be understood, too! (it is trivial, perhaps even
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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
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as the Turing program. It includes a “trace” facility,
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subroutine <code>r</code> (commented out for obscurity), to help write and
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debug Turing programs. Just the thing for some fun in a Theory
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of Computation class.</p>
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<p>The Turing machine tape is represented as a doubly linked list
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of 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
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on hand, we can recover the other link at any time. The
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variable <code>q</code> is the scan head (and a pointer at some tape cell),
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and <code>p</code> is a “previous” link. The state of the tape is stored in
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the low order bit of the pointer. Since we always allocate an
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even number of bytes, the low order bit carries no information
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(see <a href="#portability">portability</a> below.) Memory representing a tape cell is
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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
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to all zeros. Since a header can be added to any Turing
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program to write initial data and position the scan head, this
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is little loss of generality.</p>
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<p>The simulated Turing machine has a single tape with either a <code>1</code>
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or a <code>0</code> in each cell. The Turing machine language format is a
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string of three bytes. The first byte is the current state.
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The second byte is the next state. (The last bit of states is
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ignored, i.e., <code>B</code> and <code>C</code> are the same state, in an attempt to be
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able to have interesting words in the program.) The third byte
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is composed of bits. Bit <code>1</code> (<code>2&byte</code>) is the symbol scanned,
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i.e. an instruction is selected for state and for a match with
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the symbol under the scan head. Bit <code>2</code> (<code>4&byte</code>) is the new
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symbol to be 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 <code>1</code> for right.
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If bit <code>4</code> (<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
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head). (The program string is searched forward for the next
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matching instruction. If the end of the string is reached, the
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search begins again at the first of the string. Thus states
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can be used as local labels in different places.) (3) change to
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the next state, (4) print a character if indicated, (5) write the
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tape symbol, and (6) move the scan head. The cycle then repeats
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with step 1. A call to the trace routine is just before step
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2, but is commented out.</p>
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<h3 id="quick-outline-of-the-turing-program">Quick outline of the Turing program:</h3>
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<p>The previous and current Fibonacci numbers are kept in base
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1 form with the current on the right. The first three
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steps set up the first two numbers, <code>1</code> and <code>1</code>. Then
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[beginning with <code>@ (</code>] a marker of <code>III</code> is created and
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the current number is copied to the right of the
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marker. Then (beginning with <code>OV</code>) the number is
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converted to binary by repeatedly dividing by 2 leaving I
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for remainder <code>1</code>, and II for remainder <code>0</code>. Next
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(beginning with <code>WV</code>) the binary representation is
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printed and its symbols and the marker are erased.
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Finally (beginning with <code>EEn</code>) the two numbers are
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added and the current number copied to the left to
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become the previous. 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
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trace subroutine, but I felt it was important for understanding
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the program. Besides it is fun to watch the tape zooming back
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and forth as the program runs. A much better debugger or trace
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could easily be added.</p>
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<!--
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Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.
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You are free to share and adapt this file under the terms of this license:
|
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Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
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For more information, see:
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https://creativecommons.org/licenses/by-sa/4.0/
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-->
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<h1 id="inventory-for-1989paul"><a name="inventory"></a>Inventory for 1989/paul</h1>
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<p><a href="#top">Jump to top</a></p>
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<h2 id="primary-files">Primary files</h2>
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<ul>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/paul.c">paul.c</a> - entry source</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/Makefile">Makefile</a> - entry Makefile</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/paul.alt.c">paul.alt.c</a> - alternative source</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/paul.orig.c">paul.orig.c</a> - original source</li>
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<li><a href="1989_paul.tar.bz2">1989_paul.tar.bz2</a> - download entry</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 href="index.html">index.html</a> - entry home page</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/README.md">README.md</a> - markdown source for index.html</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/.entry.json">.entry.json</a> - description of entry in JSON</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1989/paul/.gitignore">.gitignore</a> - 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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</ul>
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<!--
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||
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Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.
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||
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||
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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<div class="footer">
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||
<h2>Copyright and CC BY-SA 4.0 License</h2>
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||
<p>This file and web page is:</p>
|
||
<blockquote><b>Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.</b></p></blockquote>
|
||
<p>You are free to share and adapt this file under the terms of this license:</p>
|
||
<blockquote><b>Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)</b></blockquote>
|
||
<p>For more information, see:</p>
|
||
<blockquote><a
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||
href="https://creativecommons.org/licenses/by-sa/4.0/">https://creativecommons.org/licenses/by-sa/4.0/</a></blockquote>
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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>
|
||
<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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