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<h1>The International Obfuscated C Code Contest</h1>
|
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<h2>2011/fredriksson - Most useful</h2>
|
||
<h3>Aproximate grep</h3>
|
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</div>
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<a class="Left" href="../eastman/index.html">← 2011/eastman</a>
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<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/2011/fredriksson/fredriksson.c">C code</a>
|
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<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/2011/fredriksson/Makefile">Makefile</a>
|
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<a class="Right" href="#inventory">Inventory</a>
|
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<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/2011/fredriksson/fredriksson.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%2F2011%2Ffredriksson%2Findex.html">✓</a>
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<h2 id="author">Author:</h2>
|
||
<ul>
|
||
<li>Name: <a href="../../authors.html#Kimmo_Fredriksson">Kimmo Fredriksson</a><br>
|
||
Location: <a href="../../location.html#FI">FI</a> - <em>Republic of Finland </em> (<em>Finland</em>)</li>
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<!-- BEFORE: 1st line of markdown file: 2011/fredriksson/README.md -->
|
||
<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>
|
||
<blockquote>
|
||
<p><strong>STATUS: INABIAF - please DO NOT fix</strong></p>
|
||
</blockquote>
|
||
<p>For more detailed information see <a href="../../bugs.html#2011_fredriksson">2011/fredriksson in bugs.html</a>.</p>
|
||
<h2 id="to-use">To use:</h2>
|
||
<pre><code> ./fredriksson [-icvtnk#] regexp < file</code></pre>
|
||
<h2 id="try">Try:</h2>
|
||
<pre><code> ./try.sh</code></pre>
|
||
<p><strong>NOTE</strong>: you need to be allowed to change your stack size or else the last command
|
||
in the script would likely cause the program to dump core, which is why the
|
||
script checks the exit code of <code>ulimit</code> first.</p>
|
||
<h2 id="judges-remarks">Judges’ remarks:</h2>
|
||
<p>The author of this entry was making sure that it does not win the “Best Short
|
||
Program” award. On the outside, the program behaves as an approximate <code>grep</code>.
|
||
On the inside, it is a <a href="https://en.wikipedia.org/wiki/Burrows-Wheeler_transform">Burrows-Wheeler
|
||
transform</a> decompressor
|
||
that produces the source code of the actual obfuscated approximate <code>grep</code>
|
||
program and calls it. As an exercise, try writing the compressor.</p>
|
||
<h2 id="authors-remarks">Author’s remarks:</h2>
|
||
<h3 id="approximate-grep">Approximate grep</h3>
|
||
<p>Implements a variant of <code>grep</code>.</p>
|
||
<h3 id="usage">Usage</h3>
|
||
<p>To search regexp from file, do:</p>
|
||
<pre><code> ./fredriksson [-icvtnk#] regexp < file</code></pre>
|
||
<p>Pipes might not work, see the section Limitations.
|
||
The options <code>-i</code>, <code>-c</code>, <code>-v</code> and <code>-n</code> are the classic ones:</p>
|
||
<ul>
|
||
<li><p><code>-i</code> Ignore case.</p></li>
|
||
<li><p><code>-c</code> Count only, prints the number of matches, but not the matching lines.</p></li>
|
||
<li><p><code>-v</code> Invert match.</p></li>
|
||
<li><p><code>-n</code> Prefixes each printed line by its line number (only if
|
||
<code>-c</code> was not given).</p></li>
|
||
</ul>
|
||
<p>This version of <code>grep</code> recognizes two more options, not present in normal
|
||
<code>grep</code> implementations:</p>
|
||
<ul>
|
||
<li><p><code>-kN</code> Permit <code>N</code> insertions, deletions or mismatches of characters in the
|
||
matches, aka
|
||
<a href="https://en.wikipedia.org/wiki/Edit_distance">edit-distance</a>. E.g.,
|
||
“<code>obfuscated</code>” matches “<code>obfuscation</code>”
|
||
with one deletion and two mismatches. Likewise, “<code>obfuscate</code>” and
|
||
“<code>oversimplify</code>” match with 7
|
||
<a href="https://en.wikipedia.org/wiki/Edit_distance#Formal_definition_and_properties">edit operations</a>.
|
||
The default is <code>-k0</code> (i.e. exact match).</p></li>
|
||
<li><p><code>-t</code> Add local transpositions to the set of allowed
|
||
<a href="https://en.wikipedia.org/wiki/Edit_distance#Formal_definition_and_properties">edit-operations</a>.
|
||
That is, “<code>ab</code>” matches “<code>ba</code>” with one transposition (swap), and
|
||
“<code>obfuscated</code>” matches “<code>bofsuact</code>” with three swaps and two insertions,
|
||
i.e. use <code>-tk5</code> to find this.</p></li>
|
||
</ul>
|
||
<p>Of course, one could construct a standard
|
||
<a href="https://www.regular-expressions.info">regexp</a> that matches the same
|
||
patterns, but the problem is that such a regexp grows exponentially in
|
||
size when the number of allowed <a href="https://en.wikipedia.org/wiki/Edit_distance#Formal_definition_and_properties">edit
|
||
operations</a>
|
||
is increased.</p>
|
||
<p>This version does not recognize all regular expressions, but the
|
||
following are allowed:</p>
|
||
<ul>
|
||
<li><p>Wildcard: <code>.</code> (dot) matches any character.</p></li>
|
||
<li><p>Bracket expression: list of characters enclosed by <code>[</code> and <code>]</code>,
|
||
matches any single character in the list.</p></li>
|
||
<li><p>Range expression: two characters separated by hyphen and enclosed in
|
||
brackets, matches any character that is lexicographically between the
|
||
two characters (inclusive). E.g. <code>[a-d]</code> is the same as <code>[abcd]</code>.</p></li>
|
||
</ul>
|
||
<p>The special characters must be escaped, if they are to be taken
|
||
literally (e.g. <code>\.</code> to match period). You might want to protect
|
||
these with <code>'</code>, i.e. use <code>'foo\[bar'</code> instead of <code>foo\[bar</code>. If you want to
|
||
use the literal <code>-</code> in bracket expression, protect that too (<code>\-</code>),
|
||
otherwise this is not needed. Note that the syntax differs from standard
|
||
(?) grep a bit, i.e. in plain grep you can use <code>]</code> and <code>-</code> in bracket
|
||
expressions by putting <code>]</code> as the first character, and putting <code>-</code> last.</p>
|
||
<h3 id="other-uses">Other uses</h3>
|
||
<ul>
|
||
<li>You can use this in place of <a href="https://en.wikipedia.org/wiki/Cat_(Unix)">cat</a>.
|
||
Just say</li>
|
||
</ul>
|
||
<pre><code> ./fredriksson -k3 cat < file</code></pre>
|
||
<ul>
|
||
<li>Like with <code>cat</code>, you can append line numbers too:</li>
|
||
</ul>
|
||
<pre><code> ./fredriksson -nk3 cat < file</code></pre>
|
||
<h3 id="other-features">Other features</h3>
|
||
<ul>
|
||
<li><p>It is assumed that the user knows how to feed correct input to the
|
||
program. If undefined options are given, the result is also undefined.
|
||
This is a feature.</p></li>
|
||
<li><p>It may consume huge amounts of memory, and a stack overflow may occur.
|
||
This results in Segmentation fault (or the equivalent of your favorite
|
||
system, such as Bus error). This is a feature, that can be used to detect
|
||
overly long lines in the input file, such as checking the length of one
|
||
liners in IOCCC entries, just adjust your stack size to a suitable
|
||
threshold, and search for “<code>ioccc</code>”, with option <code>-vk5</code>.</p></li>
|
||
</ul>
|
||
<h3 id="limitations-and-remarks">Limitations and remarks</h3>
|
||
<ul>
|
||
<li><p>Using warning options (such as <code>-Wall</code>) when building gives a lot of warning,
|
||
such as “<code>suggest parentheses around '&&' within '||'</code>”, “<code>value computed is not used</code>”, “<code>implicit declaration of function 'putchar'</code>”, “<code>implicit declaration of function 'getchar'</code>”, “<code>control reaches end of non-void function</code>” and “<code>format not a string literal and no format arguments</code>”.
|
||
Please ignore them all, since they just try to tell you that the source
|
||
is obfuscated.</p></li>
|
||
<li><p>Only standard input is handled. And <em>only</em> if <code>stdin</code> comes from a file,
|
||
i.e. pipes may or may not work. If you want to count only (<code>-c</code> option),
|
||
then this shouldn’t be an issue.</p></li>
|
||
<li><p>The total length of the (preprocessed) pattern is at most
|
||
<code>sizeof(long)*CHAR_BIT</code>. That does not count things like bracket expressions
|
||
or escape chars, that is, the pattern <code>'a[bcd]e\.f'</code> is 5 chars long, not
|
||
10 chars. That does not mean that the matched substring in the standard
|
||
input has this limit, as using the edit operations can make the string
|
||
longer. However, no assumptions are made for <code>sizeof(long)</code>. In fact,
|
||
you can easily use <code>long long</code> instead,</p></li>
|
||
<li><p>Depending on the file, it might require a lot of stack space. If the
|
||
program segfaults (because of this), say</p></li>
|
||
</ul>
|
||
<pre><code> ulimit -s unlimited</code></pre>
|
||
<p>cross your fingers, hope it is enough, and try again.</p>
|
||
<ul>
|
||
<li><p>Assumes C99 standard, because of the one very long line. Most C compilers
|
||
handle this just fine even in C89 mode, though.</p></li>
|
||
<li><p>The code should be reasonably portable, it assumes standard ASCII codes
|
||
for each char, and that a C compiler is on <code>$PATH</code>; the latter is hard coded
|
||
to be ‘gcc’, but any compiler would work, provided that it supports
|
||
C99, or long lines as an extension. This code has been tested on:</p>
|
||
<ul>
|
||
<li>GNU/Linux FC4, i386, gcc</li>
|
||
<li>GNU/Linux FC7, x86_64, gcc 4.1.2, tcc 0.9.24 and icc 10.0 (Btw, tcc has
|
||
its roots in IOCCC…)</li>
|
||
<li>GNU/Linux FC9, x86_64, gcc 4.?.?</li>
|
||
<li>GNU/Linux CentOS 5, gcc 4.1.2</li>
|
||
<li>GNU/Linux Ubuntu 11.04, gcc 4.5.2</li>
|
||
<li>SunOS 5.8, UltraSPARC IIIi, gcc 4.1.2</li>
|
||
<li>SunOS 5.9, UltraSPARC IIIi, gcc 4.1.1 and Sun ONE Studio 8 CC</li>
|
||
<li>AIX 5.3, IBM eServer p5-550, gcc 3.3.3 and AIX CC Version 6</li>
|
||
</ul></li>
|
||
</ul>
|
||
<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="how-this-entry-works">How this entry works:</h3>
|
||
<ul>
|
||
<li>The initialized char array includes the source code of the real program,
|
||
as well as its name and commands to build and run it, all
|
||
<a href="https://en.wikipedia.org/wiki/Burrows-Wheeler_transform">Burrows-Wheeler</a>
|
||
-transformed, then run-length-encoded with unary coding. The main program
|
||
extracts and builds that, and then calls it. More precisely, the command
|
||
to build is</li>
|
||
</ul>
|
||
<pre><code> gcc -O3 ag.c -o ag</code></pre>
|
||
<p>To change that you need to edit the char array <code>p[]</code> and (possibly) two
|
||
specially encoded constants, <code>-~('('*'(')</code> and <code>'C'*' '-'-'</code>.
|
||
The extracted source (<code>ag.c</code>) is obfuscated as well.</p>
|
||
<p>(The original version also deleted the generated source and the
|
||
corresponding binary after running it, but this feature was removed
|
||
from the submitted entry.)</p>
|
||
<ul>
|
||
<li><p>The code demonstrates several useful programming paradigms, such as:</p>
|
||
<ul>
|
||
<li>recursion to remove all loops</li>
|
||
<li>subroutines (<code>main()</code> contains several logical subroutines,
|
||
selected by the first argument)</li>
|
||
<li>function pointers</li>
|
||
</ul></li>
|
||
<li><p>Algorithmically, it incorporates the following:</p>
|
||
<ul>
|
||
<li>(inverse) Burrows-Wheeler transform (used also e.g. in <code>bzip2(1)</code>)</li>
|
||
<li>data compression (really expansion :-), run-length-encoding,
|
||
unary coding (this is why it is expansion rather than compression)</li>
|
||
<li>approximate string matching</li>
|
||
<li>dynamic programming to compute the edit distance</li>
|
||
<li>parallel computation in sequential computers (by packing
|
||
several objects into a single <code>long</code>, to speed up the dynamic
|
||
programming)</li>
|
||
<li>self extracting, compiling and running code</li>
|
||
</ul></li>
|
||
<li><p>As a C program, it demonstrates that</p>
|
||
<ul>
|
||
<li>a C subset without reserved words is complete enough,
|
||
excluding data type specific things (<code>int</code>, <code>char</code>, <code>void</code> …)</li>
|
||
<li>only letters are needed (i.e. the digits <code>0-9</code> are not)</li>
|
||
<li>only one statement is enough to code any program (plus
|
||
variable definitions)</li>
|
||
<li>white space has other uses than just indenting the code</li>
|
||
</ul></li>
|
||
<li><p>It also shows the power of boolean logic and bitwise arithmetic.</p></li>
|
||
<li><p>This is the first (?) entry in the history of IOCCC, that cannot be
|
||
totally deobfuscated by the author. This is due to the clever choice of
|
||
the actual algorithm, that is obfuscated by nature, and it is an open
|
||
research problem whether a simpler algorithm exists, with the same time
|
||
complexity.</p></li>
|
||
<li><p>The main obfuscation comes from using only arithmetic and boolean
|
||
(short-circuit) logic combined with recursion to remove all loops and
|
||
if-then-else constructs (also, no ternary <code>?:</code> constructs are present).
|
||
Two’s complement representation of integers is also abused. E.g. instead
|
||
of writing <code>x++</code> or <code>x-1</code>, it is much better to write <code>x=-~x</code> and <code>~-x</code>.</p></li>
|
||
<li><p>No numerical values, other than in the initialized char array, try</p></li>
|
||
</ul>
|
||
<pre><code> ./fredriksson -ck0 [0-9] < fredriksson.c</code></pre>
|
||
<p>This should print 1, as there is a number <code>3</code> in the char array (only).
|
||
You can also try</p>
|
||
<pre><code> ./fredriksson -ck0 [0-9] < ag.c</code></pre>
|
||
<p>after running <code>fredriksson</code> at least once (since this generates that
|
||
<code>ag.c</code> file), and this should print 0.</p>
|
||
<ul>
|
||
<li><p>The source code is best viewed with cat (or using the program itself),
|
||
instead of some editor. (This is a somewhat system dependent thing.)</p>
|
||
<p>One reason for this is that the code builds (some of the) constant
|
||
values from string literal <code>"\b"</code>, except that the backspace <code>\b</code> is not
|
||
escaped like that; the source uses the raw ASCII value (<code>010</code> octal) instead.
|
||
Thus when viewing with cat or something, that backspace erases the leading
|
||
quotation mark. Makes it appear uncompilable, and it is: if you copy-paste
|
||
the cat output from terminal to some editor, save it, the result would not
|
||
compile.</p>
|
||
<p>Some other constants are built from ASCII values of <code>char</code>s.</p>
|
||
<p>Besides of making the code hard to read, all this makes it also quite large.</p></li>
|
||
<li><p>Running it through GNU <code>indent(1)</code> or <code>bcpp(1)</code> (C beautifiers) does not beautify
|
||
it a bit. In fact, <code>indent</code> makes it only worse (at least with the default
|
||
options). Running it through the preprocessor does basically nothing,
|
||
since no <code>#define</code>s are used.</p></li>
|
||
<li><p>Some <em>abuse of the rules</em>. The number of non-whitespace and <code>;</code>, <code>{</code>
|
||
and <code>}</code> chars is below the limit, but most of the whitespace chars are
|
||
in an <em>initialized character array</em>. That is, the number of chars in the
|
||
program exceeds the 2048 limit. However, whitespace is whitespace and
|
||
the rules did not specify that these must be in between the statements.
|
||
A character is a whitespace if <code>isspace()</code> returns non-zero value. Even
|
||
if deleting even one of those chars it breaks the program! (This does not
|
||
apply to the generated source <code>ag.c</code>.)</p></li>
|
||
</ul>
|
||
<!--
|
||
|
||
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/
|
||
|
||
-->
|
||
<!-- AFTER: last line of markdown file: 2011/fredriksson/README.md -->
|
||
|
||
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|
||
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|
||
|
||
<!-- START: this line starts content generated by: bin/output-index-inventory.sh -->
|
||
|
||
<div id="inventory">
|
||
<h1 id="inventory-for-2011fredriksson">Inventory for 2011/fredriksson</h1>
|
||
</div>
|
||
<h2 id="primary-files">Primary files</h2>
|
||
<ul>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2011/fredriksson/fredriksson.c">fredriksson.c</a> - entry source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2011/fredriksson/Makefile">Makefile</a> - entry Makefile</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2011/fredriksson/fredriksson.orig.c">fredriksson.orig.c</a> - original source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2011/fredriksson/try.sh">try.sh</a> - script to try entry</li>
|
||
</ul>
|
||
<h2 id="secondary-files">Secondary files</h2>
|
||
<ul>
|
||
<li><a href="2011_fredriksson.tar.bz2">2011_fredriksson.tar.bz2</a> - download entry tarball</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2011/fredriksson/README.md">README.md</a> - markdown source for this web page</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2011/fredriksson/.entry.json">.entry.json</a> - entry summary and manifest in JSON</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2011/fredriksson/.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/2011/fredriksson/.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>
|
||
|
||
<!-- END: this line ends content from: inc/after-content.default.html -->
|
||
<!-- START: this line starts content from: inc/footer.inventory.html -->
|
||
|
||
<!--
|
||
|
||
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;"
|
||
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%2F2011%2Ffredriksson%2Findex.html" rel="nofollow">Nu HTML check this web page</a><br>
|
||
<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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</p>
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|
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