Landon Curt Noll
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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>2012/blakely - Most GIFted expressions</h2>
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<div class="navbar">
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<a class="Left Disabled" href="#">first entry</a>
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<a class="Left" href="../index.html">↑ 2012 ↑</a>
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<a class="Left" href="../deckmyn/index.html">deckmyn →</a>
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<a class="Right" href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/blakely/blakely.c">C code</a>
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<a class="Right" href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/blakely/Makefile">Makefile</a>
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<h2 id="author">Author:</h2>
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<ul>
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<li>Name: <a href="../../authors.html#Philip_Blakely">Philip Blakely</a><br>
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Location: <a href="../../location.html#GB">GB</a> - <em>United Kingdom of Great Britain and Northern Ireland</em> (<em>United Kingdom</em>)</li>
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<!-- BEFORE: 1st line of markdown file: 2012/blakely/README.md -->
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<h2 id="to-build">To build:</h2>
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<pre><code> make</code></pre>
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<h3 id="bugs-and-misfeatures">Bugs and (Mis)features:</h3>
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<p>The current status of this entry is:</p>
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<pre><code> STATUS: INABIAF - please **DO NOT** fix</code></pre>
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<p>For more detailed information see <a href="../../bugs.html#2012_blakely">2012 blakely bugs</a>.</p>
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<h2 id="to-use">To use:</h2>
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<pre><code> ./blakely "RPN formula" resolution > output.gif</code></pre>
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<h2 id="try">Try:</h2>
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<pre><code> ./try.sh</code></pre>
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<h2 id="judges-remarks">Judges’ remarks:</h2>
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<p>Several IOCCC themes (<a href="https://en.wikipedia.org/wiki/Reverse_Polish_notation">RPN
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calculator</a>, animated
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<a href="https://en.wikipedia.org/wiki/GIF">GIF</a> generator, <a href="https://en.wikipedia.org/wiki/Ray_tracing_(graphics)">ray
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tracing</a>) in one package!
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Very impressive!</p>
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<p>The checkerboard pattern in the output can be broken. Could you figure out how?</p>
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<p>Larger GIF files confuse some image viewers.</p>
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<h2 id="authors-remarks">Author’s remarks:</h2>
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<h3 id="remarks">Remarks</h3>
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<p>This program renders a generic
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<a href="https://en.wikipedia.org/wiki/Reverse_Polish_notation">RPN</a> expression in
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<a href="https://en.wikipedia.org/wiki/Ray_tracing_(graphics)">ray-traced</a> animated
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<a href="https://en.wikipedia.org/wiki/GIF">GIF</a> form. The expression in spatial
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variables <code>x</code> and <code>y</code> is specified on the command-line with the required
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resolution, and an animated GIF showing a fly-around of the resulting surface is
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output to <code>stdout</code>.</p>
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<h3 id="usage">Usage</h3>
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<p>The program should be run as:</p>
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<pre><code> ./blakely xy* 32 > pic.gif</code></pre>
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<p>where the first parameter is a
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<a href="https://en.wikipedia.org/wiki/Reverse_Polish_notation">RPN</a> expression, and the
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second is the width of the required <a href="https://en.wikipedia.org/wiki/GIF">GIF</a>, up
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to a maximum of 250.</p>
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<p>The expressions are written in <a href="https://en.wikipedia.org/wiki/Reverse_Polish_notation">Reverse Polish
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Notation</a> with the
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following characters recognised:</p>
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<pre><code> +, -, *, / - usual arithmetic operations
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^ - Exponentiation; valid for constant exponent only
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s - sin
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c - cos
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0-9 - single digit integers
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d - duplicate number on stack
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t - transpose top two elements on stack
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x - x coordinate value
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y - y coordinate value</code></pre>
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<p>NB: all arithmetic is done in double precision, so <code>23/</code> is two-thirds, rather
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than 0.</p>
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<p>The surface plotted corresponds to <code>-1 <= x,y <= 1</code> and for best results, the
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generated <code>z</code> value should lie between <code>-1</code> and <code>1</code>.</p>
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<p>If there is a division by zero, square-root of a negative number, or similar
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operation, then the results are undefined.</p>
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<h3 id="examples">Examples</h3>
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<p>For test-runs, use a resolution of 32. For simple expressions, the
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<a href="https://en.wikipedia.org/wiki/GIF">GIF</a> generation should take only
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a few seconds with a modern processor and full optimization. Runtime scales as
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<a href="https://en.wikipedia.org/wiki/Big_O_notation">O(N^3)</a> with resolution <code>N</code>,
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and more complex expressions take longer to compute. For example, increasing the
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resolution of <code>ripple.gif</code>
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to 250 took ~35 minutes to render on an <a href="https://en.wikipedia.org/wiki/Intel_Core#Core_i7">i7
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processor</a>.</p>
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<pre><code> ./blakely xy* 32 > saddle.gif
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./blakely xx*yy*1++d5*ct/ 64 > ripple.gif</code></pre>
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<h3 id="algorithm">Algorithm</h3>
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<p>A generic root-finding algorithm to find the point of intersection between a ray
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and the surface is done using a simple forward search from the eye. In order to
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make the rendering realistic, both the value of the expression, and its
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derivative with respect to <code>x</code> and <code>y</code> must be tracked. This is done using an
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obvious stack-based approach.</p>
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<h3 id="obfuscations">Obfuscations</h3>
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<p>Much of the obfuscation is achieved through the use of single-letter variables
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and <code>#define</code>s. The characters output for the <a href="https://en.wikipedia.org/wiki/GIF#File_format">GIF
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format</a> are generated in myriad
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and wonderful ways, making use of
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<a href="https://en.wikipedia.org/wiki/Exclusive_or">XOR</a>, return values from
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<code>putchar()</code>, and odd expressions. The layout is in the form of <code>X Y Z</code>.</p>
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<h3 id="limitations">Limitations</h3>
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<p>ASCII is assumed since many bytes for the
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<a href="https://en.wikipedia.org/wiki/GIF">GIF</a> output are generated from characters
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given in the source code. On compilation a few warnings about parentheses come
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up when using gcc 4.6.3, and one about no return value from <code>main()</code> (who uses
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exit codes anyway?), but clang 3.1 emits no warnings.</p>
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<h3 id="questions">Questions</h3>
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<ul>
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<li>Apart from their appearance when computing the <a href="https://en.wikipedia.org/wiki/Reverse_Polish_notation">RPN
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expression</a>, <a href="https://en.wikipedia.org/wiki/Sine_and_cosine">sin and
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cos</a> are not used.
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How do we then get the correct angles for rotation?</li>
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<li>Exactly how many times will the animation repeat?</li>
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<li>Why is there an upper limit of 250x250 for the resolution?</li>
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<li>What is the point of <code>b[0]</code>?</li>
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<li>Where are the words <code>NETSCAPE</code> and <code>GIF</code> hidden in the source?</li>
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</ul>
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<p>(Note that the author may or may not be able to answer all of the above
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questions.)</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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<div id="inventory">
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<h1 id="inventory-for-2012blakely">Inventory for 2012/blakely</h1>
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</div>
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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/2012/blakely/blakely.c">blakely.c</a> - entry source</li>
|
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/blakely/Makefile">Makefile</a> - entry Makefile</li>
|
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/blakely/blakely.orig.c">blakely.orig.c</a> - original source</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/blakely/try.sh">try.sh</a> - how to run</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="2012_blakely.tar.bz2">2012_blakely.tar.bz2</a> - download entry tarball</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/blakely/README.md">README.md</a> - markdown source for this web page</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/blakely/.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/2012/blakely/.gitignore">.gitignore</a> - list of files that should not be committed under git</li>
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<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/blakely/.path">.path</a> - directory path from top directory</li>
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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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<p>All IOCCC content including this file and web page are:</p>
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<b> Copyright © 1984-2024 by Landon Curt Noll. <a href="https://creativecommons.org/faq/#what-does-some-rights-reserved-mean">Some Rights Reserved</a>.</b>
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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%2F2012%2Fblakely%2Findex.html">Nu HTML check this web page</a></p>
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