Landon Curt Noll
a996f8d2b8
All code blocks in markdown have been intended by at least 4 spaces. We add `--tab-stop=8` to all `pandoc(1)` executions in order to set a better tab stop indentation, especially for tab intended code blocks. Changed `bin/pandoc-wrapper.sh` VERSION from "1.5.3 2024-03-26" to "1.6 2024-03-31". Fixed `1991/brnstnd/sorta.README.md` so that the sorta code is code blocks. Removed unneeded paragraph group in copyright in `inc/footer.default.html`. Fixed excess whitespace after list Author on entry `index.html` page. Changed `bin/output-index-author.sh` VERSION from "1.5.2 2024-03-26" to "1.6 2024-03-31". Performed `make www` to perform the above and test under macOS. TODO: Fix the problem of the initial line of code being extra intended. TODO: Fix excess whitespace around code that is inline.
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<title>1996/schweikh1 - Worst Abuse of the C Preprocessor</title>
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<meta name="description" content="1996 IOCCC entry schweikh1 - Worst Abuse of the C Preprocessor">
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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>1996/schweikh1 - Worst Abuse of the C Preprocessor</h2>
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<a class="Left" href="../rcm/index.html">← rcm</a>
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<a class="Left" href="../index.html">↑ 1996 ↑</a>
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<a class="Left" href="../schweikh2/index.html">schweikh2 →</a>
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<a class="Right" href="https://github.com/ioccc-src/temp-test-ioccc/1996/schweikh1/schweikh1.c">C code</a>
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<a class="Right" href="https://github.com/ioccc-src/temp-test-ioccc/1996/schweikh1/Makefile">Makefile</a>
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<a href="../../judges.html">The IOCCC Judges</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#Jens_Schweikhardt">Jens Schweikhardt</a><br>
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Location: <a href="../../location.html#DE">DE</a> - <em>Federal Republic of Germany</em> (<em>Germany</em>)</li>
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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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<h2 id="to-use">To use:</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">./schweikh1</span></span></code></pre></div>
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<h2 id="try">Try:</h2>
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<p>To find the day that Easter falls on in the current year and to show all Easter
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dates from 1582 to 2199:</p>
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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="ex">./try.sh</span></span></code></pre></div>
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<h2 id="judges-remarks">Judges’ remarks:</h2>
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<p>Look at the source. There is something very odd going on here.
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Where does the real code come from if everything is a C pre-processor
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statement?</p>
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<p>Clearly this is either the Best Use or the Worst Abuse of the
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C Preprocessor that the judges have seen this year!</p>
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<h2 id="authors-remarks">Author’s remarks:</h2>
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<h3 id="what-this-program-does">What this program does</h3>
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<p>This program is an implementation of an algorithm that calculates
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the date of the Sunday following the first full moon after the
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spring equinox. (Also known as “Easter”, defined this way by the
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Nicaean Concilium in 325 Anno Domini.) The algorithm is attributed
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to the famous mathematician <a href="https://en.wikipedia.org/wiki/Carl_Friedrich_Gauss">Carl Friedrich
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Gauss</a> [“Meyers Handbuch
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ueber das Weltall” ‘Handbook About Space’, Meyer, 5th Edition, 1973, p149] and is suitable
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for anni domini within the <a href="https://en.wikipedia.org/wiki/Gregorian_calendar">Gregorian
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Calendar</a>, that is, from ad 1582
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to ad 2199:</p>
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<pre><code> Let J be the year.
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If J is from 1582 to 1699, let M be 22, let N be 2
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If J is from 1700 to 1799, let M be 23, let N be 3
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If J is from 1800 to 1899, let M be 23, let N be 4
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If J is from 1900 to 2099, let M be 24, let N be 5
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If J is from 2100 to 2199, let M be 24, let N be 6
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Let a be the modulus of J divided by 19
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Let b be the modulus of J divided by 4
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Let c be the modulus of J divided by 7
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Let d be the modulus of (19a + M) divided by 30
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Let e be the modulus of (2b + 4c + 6d + N) divided by 7</code></pre>
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<p>The interesting Sunday is either:</p>
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<pre><code> March 22 + d + e or
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April d + e - 9 (only one of them is a valid date)</code></pre>
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<p>with the following exceptions:</p>
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<pre><code> April 26 must always be changed to April 19
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April 25 must be changed to April 18 if d is 28 and a is greater than 10</code></pre>
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<h3 id="example">Example:</h3>
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<pre><code> J = 1962, M = 24, N = 5
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a = J % 19 == 5
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b = J % 4 == 2
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c = J % 7 == 2
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d = 119 % 30 == 29
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e = 191 % 7 == 2</code></pre>
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<p>March 53 is invalid, so the result is April 22 1962.</p>
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<h3 id="why-i-think-this-is-obfuscated">Why I think this is obfuscated</h3>
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<p>Apart from the calculation of the Easter date, the definition <em>and</em>
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calculation of which are obfuscations in their own right,
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obfuscation lurks in many places. Look at those macro identifiers.
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What can be more obvious than a program that explicitly mentions the
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grammatical constructs it is composed of? If you look at K&RII A.9.3
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you will find that a compound statement consists of an opening brace
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followed by a declaration list followed by a semicolon followed by a
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statement list followed by another semicolon and a closing brace.
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Nobody can learn that by heart so I gently remind the reader by
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defining a macro that expresses this clearly (line 25). This goes up
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to the definition of a translation unit. Unfortunately, due to the
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IOCCC’s size restrictions, I had to abbreviate some syntactic
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elements. <code>ae</code> actually reads “assignment expression”. I had to stop
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at some arbitrary point, so don’t waste your time trying to find out
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how preprocessing tokens form type qualifier lists, cast expressions
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or direct abstract declarators. Assuming the reader knows about
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these easy to remember language elements is justified in my opinion.</p>
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<h3 id="the-moral">The moral:</h3>
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<p>Try to be as precise as can be and no one will comprehend what you mean.</p>
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<h4 id="the-formula">The formula:</h4>
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<pre><code> comprehension = 1/(2**precision)</code></pre>
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<h4 id="the-interpretation">The interpretation:</h4>
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<p>“Say nothing and everybody will understand.”</p>
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<p>The <code>-I/usr/include</code> in the build file is needed by gcc on Solaris because
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<code>gcc</code>’s “fixed” header in <code>gcc-lib/sparc-sun-solaris2.5/2.7.2/include/errno.h</code>
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is broken (sort of) because it has <em>two</em> identical extern declarations of errno.
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This leads to an error due to the redefinition of main. The <code>-I</code> option makes
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sure the working /usr/include/errno.h is found first, which shouldn’t cause any
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problems on other systems.</p>
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<h3 id="usage">Usage:</h3>
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<p>The program is run without arguments. It prints all dates in order.</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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<h1 id="inventory-for-1996schweikh1"><a name="inventory"></a>Inventory for 1996/schweikh1</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/1996/schweikh1/schweikh1.c">schweikh1.c</a> - entry source</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1996/schweikh1/Makefile">Makefile</a> - entry Makefile</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1996/schweikh1/schweikh1.orig.c">schweikh1.orig.c</a> - original source</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1996/schweikh1/errno.h">errno.h</a> - declare errno as an extern int</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1996/schweikh1/try.sh">try.sh</a> - how to run</li>
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<li><a href="1996_schweikh1.tar.bz2">1996_schweikh1.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/1996/schweikh1/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/1996/schweikh1/.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/1996/schweikh1/.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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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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|
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Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
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|
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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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<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></blockquote>
|
||
<p>You are free to share and adapt this file under the terms of this license:</p>
|
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<blockquote><b>Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)</b></blockquote>
|
||
<p>For more information, see:</p>
|
||
<blockquote><a
|
||
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%2F1996%2Fschweikh1%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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