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<!doctype html public "-//W3C//DTD HTML 4.0 Transitional //EN">
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<html>
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<head>
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<meta name="GENERATOR" content="mkd2html 2.2.2">
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<meta http-equiv="Content-Type"
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content="text/html; charset=utf-8"> <link rel="stylesheet"
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type="text/css"
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href="../hint.css" />
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<title></title>
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<title>Most percussive</title>
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</head>
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<body>
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<CENTER>
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<IMG SRC="/png/ioccc.png" ALT="IOCCC" height=78 width=267>
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<P><FONT size="6"><I>The International Obfuscated C Code Contest</I></FONT></P>
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<div id="bar">
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<ul>
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<li><a href="../index.html">About the 27th IOCCC</a></li>
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<li><a href="../whowon.html">27th IOCCC Winners</a></li>
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<li><a href="/index.html">IOCCC home</a></li>
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<li><a href="/winners.html">List of All Winners</a></li>
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<li><a href="/judges.html">The Judges</a></li>
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</ul>
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</div>
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<P><FONT size="6"><B>A 27<sup>th</sup> IOCCC Winner</B></FONT></P>
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</CENTER>
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<h1>Most percussive</h1>
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<p>Nathan Otterness<br/>
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<a href="https://github.com/yalue">https://github.com/yalue</a></p>
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<p>The code for this entry can be found in <a href="prog.c">prog.c</a></p>
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<h2>Judges' comments:</h2>
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<h3>To use:</h3>
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<pre><code>make
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./prog < input.mid > output.mid
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</code></pre>
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<h3>Try:</h3>
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<pre><code>wget -O cvikl.mid 'http://www.kunstderfuge.com/-/midi.asp?file=beethoven/symphony_6_1_(c)cvikl.mid'
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./prog < cvikl.mid > output.mid
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# Play output.mid with your favorite player
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wget -O entertainer.mid https://www.midiworld.com/download/3857
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./prog < entertainer.mid > output2.mid
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# Play output.mid with your favorite player
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</code></pre>
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<h3>Selected Judges Remarks:</h3>
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<p>In an entry that boasts not using literals, one would expect to see straightforward ways to produce
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small integers like <code>!(x^x)<<!(x^x)</code>, etc. but this entry is trickier than that. Deciphering what it does,
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apart from reading stdin and writing to stdout, would take a while.</p>
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<p>While doing that, you can be audially <em>entertained</em> by a sample of its output.</p>
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<h2>Author’s comments:</h2>
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<h3>MIDI “boots and cats”</h3>
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<p>This program seeks to automatically “improve” standard MIDI files (.mid) by
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adding an extra track that provides a driving drum beat to bring some
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excitement into boring video-game music rips or classical music sequences that
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otherwise only see the light of day when modern musicians import them into FL
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Studio to copy a few chords.</p>
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<h4>Prerequisites</h4>
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<p>If you’re not using Windows Media Player or already familiar with MIDI files,
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you may need to install some additional software to be able to listen to them.
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For example, on Ubuntu, I was able to play them in VLC after installing
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<code>vlc-plugin-fluidsynth</code> and <code>fluid-soundfont-gm</code>.</p>
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<p>You can obtain MIDIs in many places, but I mostly tested the program using
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files I found <a href="http://www.kunstderfuge.com/beethoven/variae.htm#Symphonies">here</a>.
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However, as discussed under the Limitations heading below, not all of them
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work correctly. I will admit to having used
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<code>http://www.kunstderfuge.com/-/midi.asp?file=beethoven/symphony_6_1_(c)cvikl.mid</code>
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for most of my testing.</p>
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<h4>Usage</h4>
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<p>Compile the program using the following command (I tested this using both
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<code>clang</code> and <code>gcc</code>):
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<code>
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$CC -pedantic -Wall -Werror -Wextra -O3 -o prog prog.c
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</code></p>
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<p>The program expects a MIDI on stdin, and writes a modified MIDI to stdout:
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<code>
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./prog <input.mid >output.mid
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</code></p>
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<p>If the program encounters an error, no output will generally be produced, and
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it will exit with a specific status code. Meanings of the various status codes
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are listed below, under the “Program error codes” heading. On success, the
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program exits with a code of 0.</p>
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<h4>Limitations</h4>
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<ol>
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<li><p>The program does not support MIDI files over 4 MB (specifically, it will
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not take input files larger than 2<sup>22</sup> - 1 bytes). This is unlikely to be a
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big limitation in practice, since even lengthy MIDIs are rarely over a
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couple hundred KB.</p></li>
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<li><p>Not all MIDIs set (or <em>correctly</em> set) their timing information, which will
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lead to the tempo of the drum beat not matching the track. This will be
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especially true for “live performance” .mid files.</p></li>
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<li><p>There may be some types of MIDI messages that the program is unable to
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correctly parse, but I have rarely seen this in practice. The largest
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cause of program failures, in my experience, has been Limitation 2.</p></li>
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</ol>
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<h4>Obfuscation notes</h4>
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<p>I had one primary goal when writing this program: include no C literals
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whatsoever. The final C file includes no numerical, string, or character
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literals. Instead, all literals have been replaced with a handful of global
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variables, which are occasionally modified throughout the file to prevent
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simple uses of find-and-replace.</p>
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<p>So, in a sense, this obfuscation is simply an intentional use of global
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variables' classic problem: absolute spaghetti code. The absence of any sort
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of literals has the added benefit of forcing any would-be reader to trace the
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contents of many variables starting from <code>main</code>, since, without literals, very
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little of the code gives any inherent visual cues as to its purpose.</p>
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<p>I already took the liberty of running <code>prog.c</code> through <code>clang-format</code>, since it
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still fits in the size limit and the formatting of the code was never intended
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to be an obfuscation technique here.</p>
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<h4>Other remarks</h4>
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<p>MIDI files are generally divided up into one or more “tracks” that play
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concurrently. While it is easy to find the positions of each of these tracks
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in the file, figuring out the amount of time each track is supposed to play is
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more difficult, and requires parsing every track in its entirety. This means
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that generating a drum beat that covers the entire piece of music requires
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parsing every track (the entire file) in order to determine the longest track.</p>
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<p>Once the program has determined the longest track in the file, it generates a
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new track, containing the simple 4-note percussion sequence, to match the
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length (in beats) of the longest-running track. It appends the new track onto
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the end of the file, taking care to update the file header, as well.</p>
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<h3>Program error codes</h3>
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<p>If the program encounters an error, it will exit with a nonzero code. The error
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codes can be interpreted as follows:</p>
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<ul>
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<li><code>1</code>: Encountered an invalid MIDI variable-length integer in the input.</li>
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<li><code>2</code>: Attempted to write an invalid MIDI variable-length integer to output.
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(This would be an internal error).</li>
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<li><code>3</code>: Encountered an unsupported MIDI event in the input.</li>
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<li><code>4</code>: Encountered a bad MIDI track header in the input.</li>
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<li><code>5</code>: The input MIDI file uses SMPTE time division, which isn’t supported.</li>
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<li><code>6</code>: Failed allocating a temporary buffer to hold a single copy of our “beat”
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messages.</li>
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<li><code>7</code>: Failed allocating a buffer to hold the new track data.</li>
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<li><code>8</code>: Failed allocating a buffer to hold the input file.</li>
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<li><code>9</code>: The input file was too large.</li>
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<li><code>10</code>: The input file’s MIDI header was incorrect (but this isn’t checked
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very thoroughly).</li>
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</ul>
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<BR>
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<HR>
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<TABLE><TR>
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<TD><a rel="license" href="https://creativecommons.org/licenses/by-sa/3.0/"><img alt="Creative Commons License" style="border-width:0" src="/png/by-sa-3.0-88x31.png" /></a></TD>
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<TD><P>© Copyright 1984-2020,
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<A HREF="/judges.html">Leo Broukhis, Simon Cooper, Landon Curt Noll</A>
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- All rights reserved<BR>
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This work is licensed under a <a rel="license" href="https://creativecommons.org/licenses/by-sa/3.0/">Creative Commons Attribution-ShareAlike 3.0 Unported License</a>.</P></TD>
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