ioccc/2015/mills2/index.html

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<!-- START: two lines up starts content from: inc/top.default.html -->

<!-- END: this line ends content from: inc/top.default.html -->
<!-- START: this line starts content from: inc/head.default.html -->

<head>
<link rel="stylesheet" href="../../ioccc.css">
<link href="https://fonts.googleapis.com/css2?family=Outfit:wght@100..900&display=swap" rel="stylesheet">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
<title>2015/mills2 - Most Compact</title>
<link rel="icon" type="image/x-icon" href="../../favicon.ico">
<meta name="description" content="2015 IOCCC entry mills2 - Most Compact">
<meta name="keywords" content="IOCCC, 2015, IOCCC 2015, IOCCC entry, mills2, Most Compact">
</head>

<!-- !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! -->
<!-- !!! DO NOT MODIFY THIS FILE - This file is generated by a tool !!! -->
<!-- !!! DO NOT MODIFY THIS FILE - This file is generated by a tool !!! -->
<!-- !!! DO NOT MODIFY THIS FILE - This file is generated by a tool !!! -->
<!-- !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! -->

<!-- END: this line ends content from: inc/head.default.html -->

<!-- -->
<!-- This web page was formed via the tool: bin/readme2index.sh -->
<!-- The content of main section of this web page came from: 2015/mills2/README.md -->
<!-- -->

<!-- !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! -->
<!-- !!! Do not modify this web page, instead modify the file: 2015/mills2/README.md !!! -->
<!-- !!! Do not modify this web page, instead modify the file: 2015/mills2/README.md !!! -->
<!-- !!! Do not modify this web page, instead modify the file: 2015/mills2/README.md !!! -->
<!-- !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! -->

<!-- Markdown content was converted into HTML via the tool: bin/md2html.sh -->

<!-- START: this line starts content from: inc/body.default.html -->

<body>

<!-- END: this line ends content from: inc/body.default.html -->
<!-- START: this line starts content from: inc/topbar.default.html -->

<div class="theader">
  <nav class="topbar">
    <div class="container">
      <div class="logo">
        IOCCC
      </div>

      <div class="topbar-items">
        <div class="item">
          <span class="item-header">
            Home
          </span>

          <div class="sub-item">
            <div class="outfit-font"><a href="../../index.html">IOCCC Home</a></div>
            <div class="outfit-font"><a href="../../years.html">Winning Entries</a></div>
            <div class="outfit-font"><a href="../../authors.html">People who have won</a></div>
            <div class="outfit-font"><a href="../../location.html">Location of authors</a></div>
          </div>
        </div>

        <div class="item">
          <span class="item-header">
            News
          </span>

          <div class="sub-item">
            <div class="outfit-font"><a href="../../news.html">IOCCC News</a></div>
            <div class="outfit-font"><a href="../../status.html">Contest status</a></div>
            <div class="outfit-font"><a href="../../next/index.html">Rules and Guidelines</a></div>
            <div class="outfit-font"><a href="../../faq.html#submit">How to enter the IOCCC</a></div>
            <div class="outfit-font"><a href="../../faq.html">FAQ</a></div>
          </div>
        </div>

        <div class="item">
          <span class="item-header">
            Bugs
          </span>

          <div class="sub-item">
            <div class="outfit-font"><a href="../../bugs.html">Bugs &amp; (mis)features</a></div>
            <div class="outfit-font"><a href="../../faq.html#fix_an_entry">Fixing IOCCC entries</a></div>
            <div class="outfit-font"><a href="../../faq.html#fix_web_site">Fixing the web site</a></div>
            <div class="outfit-font"><a href="../../faq.html#fix_author">Fixing author info</a></div>
            <div class="outfit-font"><a href="../../thanks-for-help.html">Thanks for the help</a></div>
          </div>
        </div>

        <div class="item">
          <span class="item-header">
            Judges
          </span>

          <div class="sub-item">
            <div class="outfit-font"><a href="../../judges.html">The IOCCC Judges</a></div>
            <div class="outfit-font"><a href="../../contact.html">Contacting the IOCCC</a></div>
          </div>
        </div>
      </div>
    </div>
  </nav>
</div>

<!-- END: this line ends content from: inc/topbar.default.html -->
<!-- START: this line starts content from: inc/header.default.html -->

<div class="header">
  <img src="../../png/ioccc.png" alt="IOCCC image by Matt Zucker" width=300 height=110>
  <h1>The International Obfuscated C Code Contest</h1>
  <h2>2015/mills2 - Most Compact</h2>
</div>

<!-- END: this line ends content from: inc/header.default.html -->
<!-- START: this line starts content from: inc/navbar.mid.html -->

<div class="navbar">
  <a class="Left" href="../mills1/index.html">&larr; mills1</a>
  <a class="Left" href="../index.html">&uarr; 2015 &uarr;</a>
  <a class="Left" href="../muth/index.html">muth &rarr;</a>
  <a class="Right" href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/mills2/prog.c">C code</a>
  <a class="Right" href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/mills2/Makefile">Makefile</a>
  <a class="Right" href="#inventory">Inventory</a>
</div>

<!-- END: this line ends content from: inc/navbar.mid.html -->
<!-- START: this line starts content from: inc/before-content.default.html -->

    <div class="content" id="content">

<!-- END: this line ends content from: inc/before-content.default.html -->
<!-- START: this line starts content for HTML phase 20 by: bin/output-index-author.sh via bin/md2html.sh -->

<!-- START: this line starts content generated by: bin/output-index-author.sh -->

<h2 id="author">Author:</h2>
<ul>
<li>Name: <a href="../../authors.html#Christopher_Mills">Christopher Mills</a><br>
Location: <a href="../../location.html#US">US</a> - <em>United States of America</em> (<em>United States</em>)</li>
</ul>

<!-- END: next line ends content generated by: bin/output-index-author.sh -->

<!-- END: this line ends content for HTML phase 20 by: bin/output-index-author.sh via bin/md2html.sh -->
<!-- START: this line starts content for HTML phase 21 by: bin/pandoc-wrapper.sh via bin/md2html.sh -->

<h2 id="to-build">To build:</h2>
<pre><code>    make</code></pre>
<h3 id="bugs-and-misfeatures">Bugs and (Mis)features:</h3>
<p>The current status of this entry is:</p>
<pre><code>    STATUS: INABIAF - please **DO NOT** fix</code></pre>
<p>For more detailed information see <a href="../../bugs.html#2015_mills2">2015 mills2 bugs</a>.</p>
<h2 id="to-use">To use:</h2>
<pre><code>    ./prog compressed_file.Z</code></pre>
<h2 id="try">Try:</h2>
<pre><code>    ./try.sh</code></pre>
<h2 id="judges-remarks">Judges’ remarks:</h2>
<p>Without ASCII art, the source code of this entry would have been exactly 256
bytes. Compared to <a href="../../years.html#1990_jaw">1990/jaw</a>, it is very
impressive, even taking into account the missing <code>atob</code> functionality. Now we wish
for a <code>compress(1)</code>-like compressor using a similar idea.</p>
<p>Why is the sad smiley on line 12 in that particular place?</p>
<pre><code>    c=0)                            :( O</code></pre>
<h2 id="authors-remarks">Author’s remarks:</h2>
<h3 id="the-program">The Program</h3>
<p>This program is an implementation of the unix <code>zcat(1)</code> command for printing
compressed files that have been created by the <code>compress(1)</code> command.</p>
<p>The adaptive <a href="https://en.wikipedia.org/wiki/Lempel–Ziv–Welch">LZW</a> compression
employed by <code>compress(1)</code> usually requires a fairly large amount of memory to
build the decompression tables (in fact, <code>compress(1)</code> has a command-line option
to control the size of the decompression tables, since some of the early systems
to which it was ported
(*cough*<a href="https://computerhistory.org/blog/microsoft-ms-dos-early-source-code/?key=microsoft-ms-dos-early-source-code">MS-DOS</a>*cough*)
did not have enough memory to use the full 16-bit codes). This version has no
large static or dynamic tables. It is able to decompress 16-bit files using a
single function and a few <code>int</code>s.</p>
<p>To run the program, take an existing compressed file and pass it to the program
on the command line. On the odd chance you don’t have <code>compress(1)</code> hanging about
on your system, I’ve provided compressed copies of this year’s IOCCC rules
and guidelines files. To print them, just do</p>
<pre><code>    ./prog ioccc_guidelines.txt.Z
    ./prog ioccc_rules.txt.Z</code></pre>
<h3 id="the-details">The Details</h3>
<p>The basic cleverness here comes from realizing that the compressed data is
itself an encoded version of the code dictionary. When the encoder sees
an input string that is not in its dictionary, it emits the code corresponding
to the longest prefix that is in the dictionary and adds a new entry consisting
of that code followed by the next input character. This means that when the
decoder wants to know how to decode a code, it just needs to find the spot in
the code-stream where the encoder added that entry to the dictionary. The
code at that spot is the prefix, and the first character of the following code
is the suffix. Decoding then just becomes recursion, to follow the chain of
prefixes and suffix characters.</p>
<p>Of course, it’s not nearly that simple. Finding the code in the stream is
complicated by several issues:</p>
<ul>
<li>Codes are at bit offsets within the stream, and must be extracted.</li>
<li>As codes are added to the dictionary, the code word size grows, so finding
the offset to a particular code word is involved.</li>
<li>The <code>compress(1)</code> encoder reserves a code word that clears the coding tables.
When this is encountered, the computation of offsets and bit sizes reset.</li>
<li>The <code>compress(1)</code> decoder is designed to always read a block of eight code
words at the same time, so that it need only read <code>N</code> bytes to get eight
<code>N-bit</code> code words. When the “clear” code is encountered, the entire eight-word
block is flushed (since the decoder didn’t know the word size would change).
The program needs to account for this extra flushing.</li>
<li>The end of the stream is not explicitly marked; the encoder just pads out
the output to the next byte. The decoder must notice this to know when
to stop.</li>
<li>The output stream contains a header that must be skipped.</li>
</ul>
<p>Managing all the details involved added a lovely additional layer of
obfuscation to the otherwise elegant recursive decoder. Still, the code
manages it in a remarkably small amount of code.</p>
<h3 id="limitations">Limitations</h3>
<p>The decoder doesn’t look at the header. If you supply something that is not
compressed data, it’s likely to crash in an interesting manner.</p>
<p>In particular, it doesn’t look at the third byte of the header, which encodes
the maximum code word size and whether “block mode” was used when the encoder
was run. If you use <code>compress(1)</code> in its default mode, the maximum word size
will be 16 bits and “block mode” will be enabled. You are unlikely to find
any files that don’t use “block mode”, since all versions of <code>compress(1)</code> after
2.0 (circa 1984) use it by default and have no documented way to disable it.
Reducing the bit depth is still possibly by using the <code>-b</code> flag. Modern
systems have no problem with the 200 KB or so needed for 16-bit decoder
tables, so the need for reducing the table size has passed, hence this program
always assumes 16-bits… However, should you find a file that needs a
smaller table, feel free to change the hard-coded 16 in the source into the
appropriate number and recompile.</p>
<p>In the event that you don’t supply an argument, or that argument doesn’t name
a readable file, the program will just silently exit. This is a feature.</p>
<p>The program depends on having a little-endian system. On a big-endian system
you will get a weird big-endian version of <code>compress(1)</code>, which might have come
to pass in an alternate universe where the
<a href="https://en.wikipedia.org/wiki/VAX">VAX</a> on which <code>compress(1)</code> was authored had
been big-endian. Luckily for us, it wasn’t, and neither are most of the systems
you might want to compile this for.</p>
<!--

    Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.

    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/

-->

<!-- END: this line ends content for HTML phase 21 by: bin/pandoc-wrapper.sh via bin/md2html.sh -->
<!-- START: this line starts content for HTML phase 22 by: bin/output-index-inventory.sh via bin/md2html.sh -->

<!-- START: this line starts content generated by: bin/output-index-inventory.sh -->

<div id="inventory">
<h1 id="inventory-for-2015mills2">Inventory for 2015/mills2</h1>
</div>
<p><a href="#top">Jump to top</a></p>
<h2 id="primary-files">Primary files</h2>
<ul>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/mills2/prog.c">prog.c</a> - entry source</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/mills2/Makefile">Makefile</a> - entry Makefile</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/mills2/prog.orig.c">prog.orig.c</a> - original source</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/mills2/try.sh">try.sh</a> - how to run</li>
<li><a href="ioccc_guidelines.txt.Z">ioccc_guidelines.txt.Z</a> - compressed IOCCC 2015 guidelines</li>
<li><a href="ioccc_rules.txt.Z">ioccc_rules.txt.Z</a> - compressed IOCCC 2015 rules</li>
</ul>
<h2 id="secondary-files">Secondary files</h2>
<ul>
<li><a href="2015_mills2.tar.bz2">2015_mills2.tar.bz2</a> - download entry tarball</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/mills2/README.md">README.md</a> - markdown source for this web page</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/mills2/.entry.json">.entry.json</a> - description of entry in JSON</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/mills2/.gitignore">.gitignore</a> - list of files that should not be committed under git</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/mills2/.path">.path</a> - directory path from top directory</li>
<li><a href="index.html">index.html</a> - this web page</li>
</ul>

<!-- END: next line ends content generated by: bin/output-index-inventory.sh -->

<!-- END: this line ends content for HTML phase 22 by: bin/output-index-inventory.sh via bin/md2html.sh -->
<!-- START: this line starts content from: inc/after-content.default.html -->

    </div>

<!-- END: this line ends content from: inc/after-content.default.html -->
<!-- START: this line starts content from: inc/footer.default.html -->

<!--

    Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.

    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/

-->

<div class="footer">
  <div id="copyright"><h2>Copyright and CC BY-SA 4.0 License</h2></div>
  <p>All IOCCC content including this file and web page are:</p>
  <b>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Copyright &copy; 1984-2024 by Landon Curt Noll. <a href="https://creativecommons.org/faq/#what-does-some-rights-reserved-mean">Some Rights Reserved</a>.</b>
  <p>This work is licensed by Landon Curt Noll under:</p>
  <p><b><a href="https://creativecommons.org/licenses/by-sa/4.0/?ref=chooser-v1"
  target="_blank" rel="license noopener noreferrer" style="display:inline-block;">&nbsp;&nbsp;&nbsp;&nbsp;CC BY-SA 4.0
  <img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
  src="../../png/cc.png"
  alt="cc inside circle symbol">
  <img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
  src="../../png/by.png"
  alt="person inside circle symbol">
  <img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
  src="../../png/sa.png"
  alt="arrow looping back on itself inside circle symbol">
  </a></b></p>
  <p>The <b>CC BY-SA 4.0 LEGAL CODE</b> for this license is found under:</p>
  <p>&nbsp;&nbsp;&nbsp;<b><a href="https://creativecommons.org/licenses/by-sa/4.0/legalcode.en">
  https://creativecommons.org/licenses/by-sa/4.0/legalcode.en</a></b></p>
  <p>You should <b>carefully review</b> all of the terms and conditions of the
  <a href="https://creativecommons.org/licenses/by-sa/4.0/legalcode.en">actual license</a>
  before using the licensed material.</p>
  <p>You may wish to review the <b><a href="../../license.html">highlights of some of the key
  features and terms</a></b> of the <a href="https://creativecommons.org/licenses/by-sa/4.0/legalcode.en">actual license</a>.</p>
  <h2>Coda</h2>
  <p><a href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fioccc-src.github.io%2Ftemp-test-ioccc%2F2015%2Fmills2%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>
</div>

<!-- END: this line ends content from: inc/footer.default.html -->
<!-- START: this line starts content from: inc/bottom.default.html -->

</body>
</html>

<!-- END: this line ends content from: inc/bottom.default.html -->