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<h1>The International Obfuscated C Code Contest</h1>
|
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<h2>2013/endoh1 - Most lazy SKIer</h2>
|
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<h3>SKI Combinator Calculus tool</h3>
|
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<a class="Left" href="../dlowe/index.html">← 2013/dlowe</a>
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<a class="Right" href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fwww.ioccc.org%2F2013%2Fendoh1%2Findex.html">✓</a>
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<h2 id="author">Author:</h2>
|
||
<ul>
|
||
<li>Name: <a href="../../authors.html#Yusuke_Endoh">Yusuke Endoh</a><br>
|
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Location: <a href="../../location.html#JP">JP</a> - <em>Japan</em></li>
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<!-- BEFORE: 1st line of markdown file: 2013/endoh1/README.md -->
|
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<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#2013_endoh1">2013/endoh1 in bugs.html</a>.</p>
|
||
<h2 id="to-use">To use:</h2>
|
||
<pre><code> ./endoh1 [file.lazy]</code></pre>
|
||
<h2 id="try">Try:</h2>
|
||
<pre><code> ./try.sh</code></pre>
|
||
<p>You might also enjoy running:</p>
|
||
<pre><code> cc -E endoh1.c | less</code></pre>
|
||
<h2 id="judges-remarks">Judges’ remarks:</h2>
|
||
<p>We liked this entry because it can serve as a standalone program as well as an
|
||
include file; and, as usual, because its input data is at least as obfuscated as
|
||
the program itself.</p>
|
||
<p>This entry can be considered an abuse of the GCC’s optimizer; it takes GCC about
|
||
4x longer to compile it with -O3 than without, compared to clang’s 2x.</p>
|
||
<h2 id="authors-remarks">Author’s remarks:</h2>
|
||
<h3 id="remarks">Remarks</h3>
|
||
<pre><code> less endoh1.c
|
||
gcc -o endoh1 endoh1.c
|
||
./endoh1</code></pre>
|
||
<p>… Isn’t there any more to it?</p>
|
||
<p>Yes, of course.</p>
|
||
<p>This is a tool <em>for C programmers</em> to play the <a href="http://en.wikipedia.org/wiki/SKI_combinator_calculus">SKI combinator calculus</a>,
|
||
especially, <a href="https://tromp.github.io/cl/lazy-k.html">Lazy K</a>.</p>
|
||
<p>This program will shine when it is used as a library. For example,
|
||
<a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/hello.lazy">hello.lazy</a> is a “Hello world” program written in Lazy K.</p>
|
||
<pre><code> $ lazy hello.lazy
|
||
Hello, world!</code></pre>
|
||
<p>where <code>lazy</code> is <a href="https://github.com/irori/lazyk">a reference implementation of Lazy K</a>. At the same time,
|
||
<a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/hello.lazy">hello.lazy</a> is <em>a valid C program</em> that uses <a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/endoh1.c">endoh1.c</a>
|
||
as a library.</p>
|
||
<pre><code> $ gcc -o hello -xc hello.lazy
|
||
$ ./hello
|
||
Hello, world!</code></pre>
|
||
<p>In other words, this program is a kind of <a href="http://en.wikipedia.org/wiki/Polyglot_%28computing%29">polyglot</a>.</p>
|
||
<p>The usage is simple: you just have to wrap Lazy K program with <code>#include "endoh1.c"</code>. Note that <code>#</code> is a comment in Lazy K.</p>
|
||
<h3 id="obfuscation">Obfuscation</h3>
|
||
<p>… is inherent in SKI combinator calculus :-)</p>
|
||
<p>In addition, it uses various hacks to parse SKI code as C,
|
||
and to satisfy IOCCC’s size rule.</p>
|
||
<ul>
|
||
<li>Abuse of function pointers.</li>
|
||
<li>Code duplication by macros.</li>
|
||
<li>Short coding.</li>
|
||
</ul>
|
||
<p>These led to the good obfuscation.</p>
|
||
<p>See the <a href="#how-this-entry-works">How this entry works section</a> in detail, if you need.</p>
|
||
<h3 id="limitation">Limitation</h3>
|
||
<p>This program supports only “Combinator-calculus style notation” of Lazy K.
|
||
“Unlambda style” and “Iota and Jot” style are not supported.</p>
|
||
<p>Also, it requires a space between identifiers. In short, use <code>(S K)</code> instead of
|
||
<code>(SK)</code>, “`sk”, <code>**i*i*i*ii*i*i*ii</code>, or <code>11111100011100</code>.</p>
|
||
<p>Huge memory may be required to compile the program (about 300 MB on my machine).</p>
|
||
<p>In addition, there are some limitations (and workarounds) mentioned in
|
||
the <a href="#how-this-entry-works">How this entry works section</a>.</p>
|
||
<p>But I think it would only matter when you run the attached programs.</p>
|
||
<h3 id="portability">Portability</h3>
|
||
<p>I confirmed that the program successfully worked with the following compilers:</p>
|
||
<ul>
|
||
<li>gcc 4.6.3 [Linux, Mac OS X]</li>
|
||
<li>clang 3.0 [Linux, Mac OS X]</li>
|
||
<li>tcc 0.9.26 [Linux]
|
||
<ul>
|
||
<li>N.B. tcc 0.9.25 seems to have a bug and fails to run it.</li>
|
||
</ul></li>
|
||
</ul>
|
||
<p>Recent compilers with <code>-Wall -W -Wextra -pedantic</code> say nothing.</p>
|
||
<pre><code> gcc -Wall -W -Wextra -pedantic prog.c
|
||
clang -Wall -W -Wextra -pedantic prog.c
|
||
tcc -Wall -W -Wextra -pedantic prog.c</code></pre>
|
||
<p>I think it will work on almost all platforms. I confirmed:</p>
|
||
<ul>
|
||
<li>Ubuntu Linux</li>
|
||
<li>Mac OS X</li>
|
||
<li>Raspberry PI</li>
|
||
</ul>
|
||
<p>To check whether the program is specified on the command line or included from
|
||
another source file, the program uses a predefined macro <code>__INCLUDE_LEVEL__</code>.
|
||
It is a gcc extension, and also supported by clang. If your compiler does not
|
||
support it, you cannot use the program as a library. But you can compile and
|
||
run it as a standalone program, at least. In fact, tcc does not support the
|
||
macro, but does work.</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="how-this-entry-works">How this entry works:</h3>
|
||
<p>The whole program is interpreted by macro expansion.
|
||
For example, <code>S (K I)</code> is translated to a normal C code, <code>(s)((k)(i))</code>, or
|
||
simply <code>s(k(i))</code>.</p>
|
||
<p>This expression returns an abstract syntax tree, and <a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/endoh1.c">endoh1.c</a>
|
||
evaluates it.</p>
|
||
<p>This program uses a very simple “term rewriting” approach for evaluating SKI
|
||
combinator calculus. The rewriting rules are shown in the shape of the code.</p>
|
||
<h4 id="abuse-of-function-pointers">Abuse of function pointers</h4>
|
||
<p>Consider a sequence of function applications in C:</p>
|
||
<pre><code> s(x)(x)(x)(x)...</code></pre>
|
||
<p>What type should <code>s</code> have? Unfortunately, C does <em>not</em> provide a “recursive
|
||
type”, such as <code>typedef f (*f)();</code>.</p>
|
||
<p>So, I used a heavily nested function pointer type:</p>
|
||
<pre><code> typedef void *(*(*(*...(*(f))()...)())())</code></pre>
|
||
<p>This limits how many arguments one function can be consecutively applied to.
|
||
But you can increase the number by tweaking the definition of macro <code>p</code>.</p>
|
||
<h4 id="code-duplication-by-macros">Code duplication by macros</h4>
|
||
<p>Next, we need to encode “closures”. A closure is a function together with an
|
||
environment which is a reference to non-local variable.</p>
|
||
<p>In this case, we need something that meets all of the following criteria:</p>
|
||
<ul>
|
||
<li>Is callable itself.</li>
|
||
<li>Internally possesses a reference to another closure as a non-local variable.</li>
|
||
<li>Applies the internal closure to an argument when it is called.</li>
|
||
</ul>
|
||
<p>However, no type in C is callable and has a reference at the same time.
|
||
(It is feasible by dynamic code generation, but it is far from portable.)</p>
|
||
<p>So, I addressed this issue by generating many function definitions
|
||
statically by (ab)using macros:</p>
|
||
<pre><code> void *x1; void f1(void *y) { return apply(x1, y); }
|
||
void *x2; void f2(void *y) { return apply(x2, y); }
|
||
void *x3; void f3(void *y) { return apply(x3, y); }
|
||
...
|
||
void *(h[]) = { f1, f2, f3, ... }</code></pre>
|
||
<p>and by allotting each of them when a closure is needed.</p>
|
||
<p>This leads to another limitation: the number of pre-defined closures limits how
|
||
many identifiers (<code>S</code> <code>K</code> <code>I</code>) one program can use.</p>
|
||
<p>But you can increase this number by tweaking the definition of macro <code>A</code> <code>B</code> <code>C</code>
|
||
and <code>D</code>. (Note that closures are allotted only when parsing; after the
|
||
evaluation starts, “out of closure” cannot occur.)</p>
|
||
<h4 id="short-cording">Short cording</h4>
|
||
<p>This margin is too narrow to contain a detailed explanation. Instead, I just
|
||
ask you one question. Can you tell what <code>v s[]={0,0,s+6,s+2,s+4,s,s+3,s+5,s+1};</code> is? I found this by using an <a href="https://en.wikipedia.org/wiki/Satisfiability_modulo_theories">SMT
|
||
solver</a>.</p>
|
||
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|
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|
||
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|
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|
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You are free to share and adapt this file under the terms of this license:
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|
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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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|
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|
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<div id="inventory">
|
||
<h1 id="inventory-for-2013endoh1">Inventory for 2013/endoh1</h1>
|
||
</div>
|
||
<h2 id="primary-files">Primary files</h2>
|
||
<ul>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/endoh1.c">endoh1.c</a> - entry source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/Makefile">Makefile</a> - entry Makefile</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/endoh1.orig.c">endoh1.orig.c</a> - original source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/try.sh">try.sh</a> - script to try entry</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/echo.lazy">echo.lazy</a> - lazy input file</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/hello.lazy">hello.lazy</a> - lazy input file</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/rot13.ed">rot13.ed</a> - rot13 ed script</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/tac.lazy">tac.lazy</a> - lazy input file</li>
|
||
</ul>
|
||
<h2 id="secondary-files">Secondary files</h2>
|
||
<ul>
|
||
<li><a href="2013_endoh1.tar.bz2">2013_endoh1.tar.bz2</a> - download entry tarball</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/README.md">README.md</a> - markdown source for this web page</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/.entry.json">.entry.json</a> - entry summary and manifest in JSON</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/endoh1/.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/2013/endoh1/.path">.path</a> - directory path from top level directory</li>
|
||
<li><a href="index.html">index.html</a> - this web page</li>
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</ul>
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<hr style="width:10%;text-align:left;margin-left:0">
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<h4>
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Copyright © 1984-2025 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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<div class="footer">
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<div id="copyright"><h3>Copyright © 1984-2025 by Landon Curt Noll:
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<a href="https://creativecommons.org/faq/#what-does-some-rights-reserved-mean"
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target="_blank"
|
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rel="license noopener noreferrer">Some Rights Reserved</a></h3>
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<p>
|
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This work is <b>licensed by Landon Curt Noll</b> under
|
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<b><a href="https://creativecommons.org/licenses/by-sa/4.0/?ref=chooser-v1"
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target="_blank"
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rel="license noopener noreferrer"
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style="display:inline-block;">CC BY-SA 4.0</a></b>.
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<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
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<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
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<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
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You should <b>carefully review</b> the
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rel="license noopener noreferrer">CC BY-SA 4.0 LEGAL CODE</a></b>
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before using the licensed material.<br>
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You may wish to review the
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<b><a href="../../license.html"
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target="_blank"
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rel="license noopener noreferrer">highlights of some of the key features and terms</a></b>
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of <b>CC BY-SA 4.0</b>.<br>
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<div id="coda"><h3>Coda</h3>
|
||
<p>
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<a href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fwww.ioccc.org%2F2013%2Fendoh1%2Findex.html" rel="nofollow">Nu HTML check this web page</a><br>
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