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<h1>The International Obfuscated C Code Contest</h1>
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<h2>1998/schweikh3 - Most space efficient</h2>
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<h3>Finds duplicate files that waste disk space</h3>
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<a class="Left" href="../schweikh2/index.html">← 1998/schweikh2</a>
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<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/schweikh3.orig.c">Original C</a>
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<a class="Right" href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fwww.ioccc.org%2F1998%2Fschweikh3%2Findex.html">✓</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#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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<!-- BEFORE: 1st line of markdown file: 1998/schweikh3/README.md -->
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<h2 id="to-build">To build:</h2>
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<pre><code> make all</code></pre>
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<p>The author stated:</p>
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<blockquote>
|
||
<p>In the remote event that the input has more than <code>8192</code> files with the same
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size (on systems where <code>sizeof (char *) == 4</code>, or <code>4096</code> when <code>sizeof (char *) == 8</code>), increase the manifest constant 32767 on <a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/schweikh3.c#L31">line
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31</a>.</p>
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</blockquote>
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<p>An alternate version allows one to fix this; see <a href="#alternate-code">Alternate
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code</a> below.</p>
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<h2 id="to-use">To use:</h2>
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<p>If <code>dir</code> is the directory (or a directory tree) where you keep
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all your favorite pictures off the Internet or from
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<code>alt.binaries.pictures.*</code>, do</p>
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<pre><code> find dir -type f -print | ./samefile</code></pre>
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<p>Maybe you will not need to buy another 10 GB disk to store them. :-)</p>
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<h2 id="try">Try:</h2>
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||
<p>If you’re in this winning entry’s directory:</p>
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<pre><code> ./try.sh</code></pre>
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<p>Notice that the tool finds some files that are duplicates.</p>
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<h2 id="alternate-code">Alternate code:</h2>
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<p>If you run into the problem that the author described (above) you can redefine
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the size as described; this was done with the <code>SZ</code> macro defined in the Makefile
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which if (in the code) is unset will be set to the default, 32767.</p>
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<h3 id="alternate-build">Alternate build:</h3>
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<p>If you wish to change the size to say, 55555:</p>
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<pre><code> make clobber SIZE=55555 alt</code></pre>
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<p>or whatever you wish to redefine it to.</p>
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<h2 id="judges-remarks">Judges’ remarks:</h2>
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<p>This program is not as smart as to detect identity of JPEG files with the same
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picture but with different compression levels. On the other hand compression can
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make a thing look/sound/feel different so these probably aren’t duplicates
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anyway. :-)</p>
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||
<p>Some time after this entry won, the Internet Systems Consortium (ISC) added the
|
||
samefile utility to its treasure of software gems! See the author’s page about
|
||
the tool as well at <a href="http://www.schweikhardt.net/samefile" class="uri">http://www.schweikhardt.net/samefile</a>.</p>
|
||
<h2 id="authors-remarks">Author’s remarks:</h2>
|
||
<p>The source is expected to conform to IEEE Std 1003.1-1990 (“POSIX”).
|
||
Thank God the IEEE does not standardize a coding style…</p>
|
||
<h3 id="what-this-program-does">What this program does</h3>
|
||
<p>This is best explained in the man page. The troff source for this man page can
|
||
be found in the file <a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/samefile.1">samefile.1</a>. To
|
||
render try:</p>
|
||
<pre><code> `man ./samefile.1</code></pre>
|
||
<p>Otherwise:</p>
|
||
<h3 id="samefile1-user-manuals-samefile1">SAMEFILE(1) User Manuals SAMEFILE(1)</h3>
|
||
<h4 id="name">NAME</h4>
|
||
<p><code>samefile</code> - find identical files</p>
|
||
<h4 id="synopsis">SYNOPSIS</h4>
|
||
<pre><code> ./samefile</code></pre>
|
||
<h4 id="description">DESCRIPTION</h4>
|
||
<p><code>samefile</code> reads a list of file names (one file name per
|
||
line) from <code>stdin</code>. For each file name pair with identical
|
||
contents, a line consisting of six tab separated fields is
|
||
output: The size in bytes, two file names, the character
|
||
<code>=</code> if the two files are on the same device, <code>X</code> otherwise,
|
||
and the link counts of the two files. The output
|
||
is sorted in reverse order by size.</p>
|
||
<p><code>samefile</code> uses two stages to give optimum performance.</p>
|
||
<p>In the first stage, all non-plain files are silently
|
||
ignored (directories, devices, FIFOs, sockets, symbolic
|
||
links) as well as files for which <code>stat(2)</code> or <code>open(2)</code>
|
||
fails. The result of the first stage (the file names) is
|
||
written into a binary tree with one node for every file
|
||
size. Each node is in turn a linked list of file names
|
||
along with inode and device information. It is also at
|
||
this first stage where checks for hard links are done.
|
||
For any inode only one filename will be added to the
|
||
binary tree.</p>
|
||
<p>In the second stage all files having the same size are
|
||
compared against each other. The rules of mathematical
|
||
logic are applied to reduce work and output noise: if
|
||
files <code>A</code>, <code>B</code>, and <code>C</code> have the same size and samefile finds
|
||
that <code>A = B</code> and <code>A = C</code> then it will not compare <code>B</code> against <code>C</code>
|
||
(and will not output a line for <code>B</code> and <code>C</code>) but only for <code>A = B</code> and <code>A = C</code>. The algorithm will detect equality across
|
||
arbitrarily long chains. Note however, that because only
|
||
the first filename per inode gets into the first stage,
|
||
the output for a group of identical files with different
|
||
inode numbers is also minimized. Suppose you have six
|
||
identical files of size 100 in an inode group consisting
|
||
of the three inodes with numbers 10, 20 and 30:</p>
|
||
<pre><code> $ ls -i # output edited for readability:
|
||
10 file1 20 file4 30 file6
|
||
10 file2 20 file5
|
||
10 file3
|
||
$ ls | ./samefile
|
||
100 file1 file4 = 3 2
|
||
100 file1 file6 = 3 1</code></pre>
|
||
<p>The sum of the sizes in the first column is the amount of
|
||
disk space you could gain by making all 6 files links to
|
||
only one file or remove all but one of the files. To be
|
||
precise, disk space is allocated in blocks - you will
|
||
probably gain two blocks here, rather than 200 bytes.
|
||
Note that it is not enough to just remove <code>file4</code> and <code>file6</code>
|
||
(you would gain only 100 bytes because <code>file5</code> still
|
||
exists.)</p>
|
||
<h4 id="limitations">LIMITATIONS</h4>
|
||
<p><code>samefile</code> was written with no limits in mind. The number of
|
||
input lines is unlimited. The size of the actual files is
|
||
only limited by available virtual memory needed to compare
|
||
one pair of files. The only hard limit is the constraint
|
||
that there should not be more than about <code>8192</code> files having
|
||
the same size. Experience has shown that there are rarely
|
||
more than a couple dozen files of the same size.</p>
|
||
<h4 id="examples">EXAMPLES</h4>
|
||
<p>For everybody:</p>
|
||
<p>What are the duplicates under my home directory?</p>
|
||
<pre><code> find $HOME | ./samefile</code></pre>
|
||
<p>For the sysadmin folks:</p>
|
||
<p>Report all duplicate files under /usr larger than 16k:</p>
|
||
<pre><code> find /usr -size +16384c -a -type f | ./samefile</code></pre>
|
||
<p>For the ftp and WWW admins:
|
||
How much space is wasted below our site’s /pub directory?</p>
|
||
<pre><code> find /pub -type f | samefile | awk '{sum += $1} END {print sum}'</code></pre>
|
||
<h4 id="exit-status">EXIT > STATUS</h4>
|
||
<p>If <code>samefile</code> runs out of memory the exit status is 1, zero
|
||
otherwise.</p>
|
||
<h4 id="see-also">SEE ALSO</h4>
|
||
<p><code>find(1)</code>, <code>ln(1)</code>, <code>rm(1)</code></p>
|
||
<h3 id="notice-to-those-who-wish-for-a-greater-challenge">NOTICE to those who wish for a greater challenge</h3>
|
||
<p><strong>If you want a greater challenge, don’t read any further</strong>:
|
||
just try to understand the program via the source.</p>
|
||
<p>If you get stuck, come back and read below for additional hints and information.</p>
|
||
<h3 id="why-i-think-it-is-obfuscated">Why I think it is obfuscated</h3>
|
||
<ul>
|
||
<li>The code is commented but this gives only an <em>extremely</em> faint clue.</li>
|
||
<li>The layout does not reflect the program structure, or does it?</li>
|
||
<li>The data structure the program builds is an ordered binary tree
|
||
where each node consists of a linked list. This is probably too
|
||
heavy to comprehend for N percent of all programmers ;-)</li>
|
||
<li>The tree is built and traversed by recursive function calls.</li>
|
||
<li>Why does this program look at <code>dev_t</code> and <code>ino_t</code>? Heavy wizardry.</li>
|
||
<li>Can you find out how the algorithm works that detects identity
|
||
of files across arbitrarily long chains? In my private unobfuscated
|
||
source there are 17 lines describing just that. A classical case for
|
||
the well known <code>/* You're not supposed to understand this */</code> comment.</li>
|
||
<li>Would Dijkstra consider this <code>goto</code> harmful?</li>
|
||
<li>The only string literal is split in more than a dozen substrings.</li>
|
||
<li>For the task at hand the code is pretty terse. Some dynamic memory
|
||
is even freed as soon as it’s no longer needed. I have tried to
|
||
make the preprocessor directives as short as possible. This means
|
||
no spaces after <code>#include</code> and no spaces after some of the macro
|
||
names.</li>
|
||
</ul>
|
||
<p>Are you an algorithms guru? If so you should know why the output
|
||
appears sorted without any use of <code>qsort(3)</code> or <code>system("sort")</code>.</p>
|
||
<p>Rewrite (hah!) the program to use memory mapping of files instead
|
||
of <code>read(2)</code>. Does this affect performance noticeably?</p>
|
||
<p>It’s easy to write a script that takes <code>samefile</code>’s output and
|
||
hard links (or symlinks) identical files. Writing such a script is
|
||
left as an exercise for the deobfuscator.</p>
|
||
<p>When you run <code>samefile</code> on some directory tree, try to estimate
|
||
how much you think it will find. Is the actual result anywhere
|
||
near your estimate? How many copies of the GPL <code>COPYING</code> file
|
||
are there on your filesystems? :-)</p>
|
||
<p>In the remote event that the input has more than <code>8192</code> files with
|
||
the same size (on systems where <code>sizeof (char *) == 4</code>, or <code>4096</code> when
|
||
<code>sizeof (char *) == 8</code>), increase the manifest constant 32767 on line
|
||
31.</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/
|
||
|
||
-->
|
||
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|
||
|
||
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|
||
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|
||
|
||
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|
||
|
||
<div id="inventory">
|
||
<h1 id="inventory-for-1998schweikh3">Inventory for 1998/schweikh3</h1>
|
||
</div>
|
||
<h2 id="primary-files">Primary files</h2>
|
||
<ul>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/schweikh3.c">schweikh3.c</a> - entry source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/Makefile">Makefile</a> - entry Makefile</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/schweikh3.alt.c">schweikh3.alt.c</a> - alternate source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/schweikh3.orig.c">schweikh3.orig.c</a> - original source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/samefile.1.dupe">samefile.1.dupe</a> - copy of samefile man page</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/samefile.1">samefile.1</a> - samefile man page</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/try.sh">try.sh</a> - script to try entry</li>
|
||
</ul>
|
||
<h2 id="secondary-files">Secondary files</h2>
|
||
<ul>
|
||
<li><a href="1998_schweikh3.tar.bz2">1998_schweikh3.tar.bz2</a> - download entry tarball</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/README.md">README.md</a> - markdown source for this web page</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/.entry.json">.entry.json</a> - entry summary and manifest in JSON</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/.gitignore">.gitignore</a> - list of files that should not be committed under git</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1998/schweikh3/.path">.path</a> - directory path from top level directory</li>
|
||
<li><a href="index.html">index.html</a> - this web page</li>
|
||
</ul>
|
||
<hr style="width:10%;text-align:left;margin-left:0">
|
||
<h4>
|
||
Jump to: <a href="#">top</a>
|
||
</h4>
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||
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|
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</div>
|
||
|
||
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|
||
|
||
<!--
|
||
|
||
Copyright © 1984-2025 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"><h3>Copyright © 1984-2025 by Landon Curt Noll:
|
||
<a href="https://creativecommons.org/faq/#what-does-some-rights-reserved-mean"
|
||
target="_blank"
|
||
rel="license noopener noreferrer">Some Rights Reserved</a></h3>
|
||
<p>
|
||
This work is <b>licensed by Landon Curt Noll</b> under
|
||
<b><a href="https://creativecommons.org/licenses/by-sa/4.0/?ref=chooser-v1"
|
||
target="_blank"
|
||
rel="license noopener noreferrer"
|
||
style="display:inline-block;">CC BY-SA 4.0</a></b>.
|
||
<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;"
|
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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"><br>
|
||
You should <b>carefully review</b> the
|
||
<b><a href="https://creativecommons.org/licenses/by-sa/4.0/legalcode.en"
|
||
target="_blank"
|
||
rel="license noopener noreferrer">CC BY-SA 4.0 LEGAL CODE</a></b>
|
||
before using the licensed material.<br>
|
||
You may wish to review the
|
||
<b><a href="../../license.html"
|
||
target="_blank"
|
||
rel="license noopener noreferrer">highlights of some of the key features and terms</a></b>
|
||
of <b>CC BY-SA 4.0</b>.<br>
|
||
</p>
|
||
</div>
|
||
|
||
<div id="coda"><h3>Coda</h3>
|
||
<p>
|
||
<a href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fwww.ioccc.org%2F1998%2Fschweikh3%2Findex.html" rel="nofollow">Nu HTML check this web page</a><br>
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||
<a href="#top">Jump to top</a> <a href="#content">Jump to Content</a> <a href="#inventory">Jump to Inventory</a><br>
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