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<title>1992/buzzard.1 - Most Obfuscated Algorithm</title>
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<img src="../../png/ioccc.png" alt="IOCCC image by Matt Zucker" width=300 height=110>
<h1>The International Obfuscated C Code Contest</h1>
<h2>1992/buzzard.1 - Most Obfuscated Algorithm</h2>
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<a class="Left" href="../ant/index.html">&larr; ant</a>
<a class="Left" href="../index.html">&uarr; 1992 &uarr;</a>
<a class="Left" href="../buzzard.2/index.html">buzzard.2 &rarr;</a>
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<h2 id="author"><a name="author"></a>Author:</h2>
<ul>
<li>Name: <a href="../../authors.html#Sean_Barrett">Sean Barrett</a><br>
Location: <a href="../../location.html#ZZ">ZZ</a> <br><br></li>
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<h2 id="to-build">To build:</h2>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="fu">make</span> all</span></code></pre></div>
<h2 id="to-use">To use:</h2>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="ex">./buzzard.1</span> num num</span></code></pre></div>
<h2 id="try">Try:</h2>
<div class="sourceCode" id="cb3"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="ex">./try.sh</span></span></code></pre></div>
<h2 id="judges-remarks">Judges’ remarks:</h2>
<p>To see good C Preprocessor buzzard.1, try:</p>
<div class="sourceCode" id="cb4"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="fu">make</span> babble.cppcb</span>
<span id="cb4-2"><a href="#cb4-2" aria-hidden="true" tabindex="-1"></a><span class="fu">cat</span> babble.cppcb</span></code></pre></div>
<p>Notice how many statements it takes to do anything useful?</p>
<h2 id="authors-remarks">Author’s remarks:</h2>
<p>What you shouldn’t think about <code>buzzard.1</code>:</p>
<p><code>buzzard.1</code> doesn’t just do a mass of
<code>#define</code>s as its obfuscation.</p>
<h3 id="what-you-should-be-glad-about">What you should be glad
about:</h3>
<p>I didn’t just submit the post-C-preprocessed output as an entry.</p>
<h4 id="cute-trick-warning">Cute trick warning</h4>
<p><code>buzzard.1</code> contains only a numeric
<code>printf(3)</code>, yet sometimes it prints out short strings.</p>
<h3 id="what-it-does">What it does</h3>
<p><code>buzzard.1</code> is a simple mathematical program. It expects
two numeric arguments.</p>
<div class="sourceCode" id="cb5"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a><span class="ex">./buzzard.1</span> 0 <span class="op">&lt;</span>num<span class="op">&gt;</span></span></code></pre></div>
<p>will print out the factorial of <code>&lt;num&gt;</code>.</p>
<div class="sourceCode" id="cb6"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb6-1"><a href="#cb6-1" aria-hidden="true" tabindex="-1"></a><span class="ex">./buzzard.1</span> <span class="op">&lt;</span>num1<span class="op">&gt;</span> <span class="op">&lt;</span>num2<span class="op">&gt;</span></span></code></pre></div>
<p>will print out the largest common factor of <code>num1</code> and
<code>num2</code>.</p>
<div class="sourceCode" id="cb7"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true" tabindex="-1"></a><span class="ex">./buzzard.1</span> 1 <span class="op">&lt;</span>num2<span class="op">&gt;</span></span></code></pre></div>
<p>will print out a factor of <code>num2</code> if it’s composite, or
else it will print a string informing you that <code>num2</code> is
prime.</p>
<p>If the first argument is less than 0, it prints out an error
message.</p>
<h3 id="what-it-is">What it is</h3>
<p><code>buzzard.1</code> is a translator from a pseudo-assembly
language into a subset of C suitable for execution on Charles Babbage’s
Analytical Engine. Or rather, the <code>#define</code>s in
<code>buzzard.1</code> are that translator. The rest of
<code>buzzard.1</code> is a <code>buzzard.1</code> program. If you run
the whole mess through CPP and a beautifier, you will see that all you
have is a loop that runs until a variable is not 0, and a sequence of
assignment statements. The assignment statements are all of the form
<code>a op= b</code> or <code>a = b</code>. The Engine actually allowed
‘a = b op c’. Only <code>+</code>, <code>-</code>, <code>/</code>, and
<code>*</code> are used–no boolean or bitwise operators. The infinite
loop could have been simulated on the AE by connecting the
already-processed card stack to the input card stack.</p>
<h3 id="how-to-try-to-understand-it">How to try to understand it</h3>
<p><em>Don’t</em> expand the <code>#define</code>s! Rather, decipher
what they do. Some of them are mere obfuscation fodder, put in to
encourage you to run it through CPP.</p>
<h3 id="what-it-doesnt-do-quite-right-as-an-emulator">What it doesn’t do
quite right as an emulator</h3>
<p>Because of the definitional constraints, calls to
<code>atoi(argv[#])</code> also appear inside the loop. These could be
put outside–the initial values of the “registers” on the AE–but the
macro conventions being used didn’t lend themselves to it.</p>
<h3 id="theoretical-observations">Theoretical observations</h3>
<p>The simulated comparison operations only work with a certain range of
numbers; numbers that are too large will cause the output code to fail
to simulate the input code. This means that this implementation of
<code>buzzard.1</code> would not be Turing-complete, even if the AE
could process indefinitely-sized numbers. However, this is actually a
constraint that no actual computer can meet, either, so we can conclude
that if an AE, with card bins connected as suggested above, were hooked
up to a memory unit of sufficient size, it would be as Turing complete
as any existing machine (or, for those who interpret that excessively
critically, i.e. “not at all” for both, we can simply say that the AE
could simulate any existing machine–although not quickly). This would be
a good place to site some references on the AE, but I don’t have
any.</p>
<h3
id="definition-of-the-input-language-to-buzzard.1-or-what-exactly-do-all-the-macros-do">Definition
of the input language to buzzard.1 (OR What Exactly Do All The Macros
Do?)</h3>
<p>[Don’t read this unless you’re stumped!]</p>
<pre><code>
MACRO FUNCTION MNEMONIC
V begin variable declarations Variable
C begin program Code
Q(b,a) let b = a eQuals
A(c,a,b) let c = a + b Add
S(c,a,b) let c = a - b Subtract
D(c,a,b) let c = a / b, where b is a *constant* Divide
U(c,a,b) let c = a / b, where b is anything Unknown
M(c,a,b) let c = a * b Multiply
O(c,a,b) let c = a boolean-or b (a,b are 0 or 1) Or
B(b, a) let b = boolean value of a Boolean
P(b, a) let b = 1 if a&gt;0, else 0. Positive
l emit next sequential label Label
J(x) goto label #x Jump
Z(a,d) if a is 0 goto d (a is 0 or 1) Zero
E(a,d) if a is 1 goto d (a is 0 or 1) Else
H halt Haly
K(x) let x = number of cmd line arguments Kount
G(x,y) let x = the value if the yth argument Get argument
T end of code; begin output section Terminate
X(y) print out hexadecimal value of y heXadecimal
T end of output section and program Terminate</code></pre>
<p>You can figure out the other macros yourself. In the sample program,
I’ve actually implemented subroutines by saving a return address in a
variable and then jumping to a routine– specifically, a routine that
converts a number into BCD, so it can be output by the hexadecimal
output statement.</p>
<h3 id="how-it-works-i.e.-how-to-get-useful-programs-from-a-op-b">How it
works, i.e., how to get useful programs from a op= b</h3>
<p>The essential statement to be able to make interesting programs is
the conditional (given that we have loops). Since all you can do in the
given operation output set is assignment, we implement “conditional
assignment”:</p>
<div class="sourceCode" id="cb9"><pre class="sourceCode c"><code class="sourceCode c"><span id="cb9-1"><a href="#cb9-1" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="op">(</span>x<span class="op">)</span> y <span class="op">=</span> z<span class="op">;</span></span></code></pre></div>
<p>To implement this, we constrain <code>x</code> to be either 0 or 1,
and simply compute:</p>
<div class="sourceCode" id="cb10"><pre class="sourceCode c"><code class="sourceCode c"><span id="cb10-1"><a href="#cb10-1" aria-hidden="true" tabindex="-1"></a>y <span class="op">=</span> <span class="op">(</span>z <span class="op">*</span> x<span class="op">)</span> <span class="op">+</span> <span class="op">(</span>y <span class="op">*</span> <span class="op">(</span><span class="dv">1</span><span class="op">-</span>x<span class="op">));</span></span></code></pre></div>
<p>This is more obscured by factoring out common terms and restricting
ourselves to two operand operations:</p>
<div class="sourceCode" id="cb11"><pre class="sourceCode c"><code class="sourceCode c"><span id="cb11-1"><a href="#cb11-1" aria-hidden="true" tabindex="-1"></a>temp <span class="op">=</span> z<span class="op">;</span> <span class="op">(</span>temp <span class="op">==</span> z<span class="op">)</span></span>
<span id="cb11-2"><a href="#cb11-2" aria-hidden="true" tabindex="-1"></a>temp <span class="op">-=</span> y<span class="op">;</span> <span class="op">(</span>temp <span class="op">==</span> z<span class="op">-</span>y<span class="op">)</span></span>
<span id="cb11-3"><a href="#cb11-3" aria-hidden="true" tabindex="-1"></a>temp <span class="op">*=</span> x<span class="op">;</span> <span class="op">(</span>temp <span class="op">==</span> <span class="op">(</span>z<span class="op">-</span>y<span class="op">)*</span>x<span class="op">)</span></span>
<span id="cb11-4"><a href="#cb11-4" aria-hidden="true" tabindex="-1"></a>y <span class="op">+=</span> temp<span class="op">;</span> <span class="op">(</span>y <span class="op">==</span> <span class="op">(</span>z<span class="op">-</span>y<span class="op">)*</span>x <span class="op">+</span> y<span class="op">)</span></span>
<span id="cb11-5"><a href="#cb11-5" aria-hidden="true" tabindex="-1"></a> <span class="op">(</span> <span class="op">==</span> z<span class="op">*</span>x <span class="op">-</span> y<span class="op">*</span>x <span class="op">+</span> y<span class="op">)</span></span>
<span id="cb11-6"><a href="#cb11-6" aria-hidden="true" tabindex="-1"></a> <span class="op">(</span> <span class="op">==</span> z<span class="op">*</span>x <span class="op">+</span> y<span class="op">*(</span><span class="dv">1</span><span class="op">-</span>x<span class="op">))</span></span></code></pre></div>
<p>Next we imagine we have a <a
href="https://en.wikipedia.org/wiki/Program_counter">pc</a>. “I’m
supposed to execute statement pc next”, says our emulator. But suppose
we’re not currently coming up on statement pc. To handle this, we simply
make every operation conditional on the pc having the correct value:</p>
<div class="sourceCode" id="cb12"><pre class="sourceCode c"><code class="sourceCode c"><span id="cb12-1"><a href="#cb12-1" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="op">(</span>pc <span class="op">==</span> some_constant<span class="op">)</span> y <span class="op">=</span> z<span class="op">;</span></span></code></pre></div>
<p>To combine this with other operations, we simply multiply by our
(<code>pc == some_constant</code>) flag right after the above
<code>temp *= x</code>.</p>
<p>To evaluate <code>pc == some_constant</code> requires one more trick.
We assume that numbers can only be in some limited range. Then we use
successive additions and divisions to reduce that number down to
<code>-1</code>, <code>0</code>, or <code>1</code>. You could, for
instance, do this by using mod by <code>2</code> and div by
<code>2</code> to count bits, stopping after, say, <code>32</code>
iterations. The number you get is between <code>0..32</code>, so another
<code>6</code> iterations on it reduces it to <code>0..6</code>. Three
iterations on this produces <code>0..2</code> (<code>3</code> would be
<code>7</code>), and then two iterations on this produces 0 or 1.
Instead I use a shorter two-divide approach that assumes I’m allowed to
use numbers slightly larger than the numbers I’m operating on.</p>
<p>A similar approach is used to detect positive numbers.</p>
<p>Note that the obvious code to compute <code>y/x</code> will not work
correctly, because every value is computed, even if the pc is not set
correctly; if <code>x</code> is ever <code>0</code> when the real C code
reaches this computation the program will die. (This was discovered the
hard way.) The solution is to stick <code>x</code> in a temporary, and
if the current code is not about to be executed, set the temporary to
<code>1</code>.</p>
<p>Thanks to Bill Pugh for bringing the loop-ability of the AE to my
attention.</p>
<p><code>buzzard.1</code> was originally named ‘cb’, for obvious
reasons, and is dedicated to the memory of Charles Barrett.</p>
<h2 id="copyright-and-cc-by-sa-4.0-license">Copyright and CC BY-SA 4.0
License:</h2>
<p>This file is Copyright (c) 2023 by Landon Curt Noll. All Rights
Reserved. You are free to share and adapt this file under the terms of
this license:</p>
<pre><code>Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)</code></pre>
<p>For more information, see:
https://creativecommons.org/licenses/by-sa/4.0/</p>
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<h1 id="inventory-for-1992buzzard.1"><a name="inventory"></a>Inventory
for 1992/buzzard.1</h1>
<h2 id="primary-files">Primary files</h2>
<ul>
<li><a href="index.html">index.html</a> - entry home page</li>
<li><a
href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1992/buzzard.1/buzzard.1.c">buzzard.1.c</a>
- winning source</li>
<li><a
href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1992/buzzard.1/Makefile">Makefile</a>
- entry Makefile</li>
<li><a
href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1992/buzzard.1/buzzard.1.orig.c">buzzard.1.orig.c</a>
- original source</li>
<li><a
href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1992/buzzard.1/try.sh">try.sh</a>
- how to run</li>
<li><a href="1992_buzzard.1.tar.bz2">1992_buzzard.1.tar.bz2</a> -
download winning source</li>
</ul>
<h2 id="secondary-files">Secondary files</h2>
<ul>
<li><a
href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1992/buzzard.1/.entry.json">.entry.json</a>
- description of entry in JSON</li>
<li><a
href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1992/buzzard.1/.gitignore">.gitignore</a>
- list of files that should not be committed under git</li>
<li><a href=".path">.path</a> - directory path from top directory</li>
<li><a
href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1992/buzzard.1/README.md">README.md</a>
- markdown source for index.html</li>
</ul>
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