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<h1>The International Obfuscated C Code Contest</h1>
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<h2>1992/buzzard.1 - Most obfuscated algorithm</h2>
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<h3>print factorial or gcd or prime test w/Babbage-like engine</h3>
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<a class="Left" href="../ant/index.html">← 1992/ant</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#Sean_Barrett">Sean Barrett</a><br>
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Location: <a href="../../location.html#US">US</a> - <em>United States of America</em> (<em>United States</em>)</li>
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<h2 id="to-build">To build:</h2>
|
||
<pre><code> make all</code></pre>
|
||
<h2 id="to-use">To use:</h2>
|
||
<pre><code> ./buzzard.1 num num</code></pre>
|
||
<h2 id="try">Try:</h2>
|
||
<pre><code> ./try.sh</code></pre>
|
||
<h2 id="judges-remarks">Judges’ remarks:</h2>
|
||
<p>To see good C Preprocessor buzzard.1, try:</p>
|
||
<pre><code> make babble.cppcb
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cat babble.cppcb</code></pre>
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||
<p>Notice how many statements it takes to do anything useful?</p>
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||
<h2 id="authors-remarks">Author’s remarks:</h2>
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||
<h3 id="what-you-shouldnt-think-about-buzzard.1">What you shouldn’t think about <code>buzzard.1</code>:</h3>
|
||
<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>
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||
<p>I didn’t just submit the post-C-preprocessed output as an entry.</p>
|
||
<h3 id="cute-trick-warning">Cute trick warning</h3>
|
||
<p><code>buzzard.1</code> contains only a numeric <code>printf(3)</code>, yet sometimes it prints out
|
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short strings.</p>
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||
<h3 id="what-it-does">What it does</h3>
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||
<p><code>buzzard.1</code> is a simple mathematical program. It expects two numeric
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arguments.</p>
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<pre><code> ./buzzard.1 0 <num></code></pre>
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<p>will print out the factorial of <code><num></code>.</p>
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<pre><code> ./buzzard.1 <num1> <num2></code></pre>
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<p>will print out the largest common factor of <code>num1</code> and <code>num2</code>.</p>
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||
<pre><code> ./buzzard.1 1 <num2></code></pre>
|
||
<p>will print out a factor of <code>num2</code> if it’s composite, or else
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||
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 Divide
|
||
constant
|
||
|
||
U(c,a,b) let c = a / b,
|
||
where b is Unknown
|
||
anything
|
||
|
||
M(c,a,b) let c = a * b Multiply
|
||
|
||
O(c,a,b) let c = a Or
|
||
boolean-or
|
||
b (a,b are
|
||
0 or 1)
|
||
|
||
B(b, a) let Boolean
|
||
b = boolean
|
||
value of a
|
||
|
||
P(b, a) let b = 1 if
|
||
a>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 Zero
|
||
0 or 1)
|
||
|
||
E(a,d) if a is 1
|
||
goto d Else
|
||
(a is 0 or 1)
|
||
|
||
H halt Halt
|
||
|
||
K(x) let x = number
|
||
of cmdline Kount
|
||
arguments
|
||
|
||
G(x,y) let x = the
|
||
value
|
||
of the yth Get arg
|
||
argument
|
||
|
||
T end of code;
|
||
begin output Terminate
|
||
section
|
||
|
||
X(y) print hex
|
||
value of y heX
|
||
|
||
T end of output Terminate
|
||
section
|
||
and program</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>
|
||
<pre><code> if (x) y = z;</code></pre>
|
||
<p>To implement this, we constrain <code>x</code> to be either 0 or 1, and
|
||
simply compute:</p>
|
||
<pre><code> y = (z * x) + (y * (1-x));</code></pre>
|
||
<p>This is more obscured by factoring out common terms and restricting
|
||
ourselves to two operand operations:</p>
|
||
<pre><code> temp = z; (temp == z)
|
||
temp -= y; (temp == z-y)
|
||
temp *= x; (temp == (z-y)*x)
|
||
y += temp; (y == (z-y)*x + y)
|
||
( == z*x - y*x + y)
|
||
( == z*x + y*(1-x))</code></pre>
|
||
<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>
|
||
<pre><code> if (pc == some_constant) y = z;</code></pre>
|
||
<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 <code>cb</code>, for obvious reasons, and is
|
||
dedicated to the memory of Charles Barrett.</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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<div id="inventory">
|
||
<h1 id="inventory-for-1992buzzard.1">Inventory for 1992/buzzard.1</h1>
|
||
</div>
|
||
<h2 id="primary-files">Primary files</h2>
|
||
<ul>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1992/buzzard.1/buzzard.1.c">buzzard.1.c</a> - entry source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1992/buzzard.1/Makefile">Makefile</a> - entry Makefile</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1992/buzzard.1/buzzard.1.orig.c">buzzard.1.orig.c</a> - original source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1992/buzzard.1/try.sh">try.sh</a> - script to try entry</li>
|
||
</ul>
|
||
<h2 id="secondary-files">Secondary files</h2>
|
||
<ul>
|
||
<li><a href="1992_buzzard.1.tar.bz2">1992_buzzard.1.tar.bz2</a> - download entry tarball</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1992/buzzard.1/README.md">README.md</a> - markdown source for this web page</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1992/buzzard.1/.entry.json">.entry.json</a> - entry summary and manifest in JSON</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/1992/buzzard.1/.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/1992/buzzard.1/.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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Jump to: <a href="#">top</a>
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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:
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||
|
||
Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
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|
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For more information, see:
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|
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https://creativecommons.org/licenses/by-sa/4.0/
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|
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-->
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<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>
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||
<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"
|
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rel="license noopener noreferrer"
|
||
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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src="../../png/cc.png"
|
||
alt="cc inside circle symbol">
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<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
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src="../../png/by.png"
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alt="person inside circle symbol">
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<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
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src="../../png/sa.png"
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alt="arrow looping back on itself inside circle symbol"><br>
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You should <b>carefully review</b> the
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<b><a href="https://creativecommons.org/licenses/by-sa/4.0/legalcode.en"
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target="_blank"
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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>
|
||
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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</p>
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</div>
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|
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<div id="coda"><h3>Coda</h3>
|
||
<p>
|
||
<a href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fwww.ioccc.org%2F1992%2Fbuzzard.1%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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