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ioccc/2015/burton/obfuscation.html
Landon Curt Noll f29b37e49a improve HTML menus, add social.html, prep for IOCCC28 winners
Prepare for the winners of **IOCCC28**.

> However these are not the 2024 droids you are looking for.  :-)

The HTML menu (both JavaScript and non-JavaScript) has been updated.

The `Status -> Rules and guidelines' have been replaced with two
separate menus `Status -> IOCCC rules` and `Status -> IOCCC guidelines`.

Added a new top level `social.html` page: built from a new `social.md`.

Sorted rules for building specific web pages in the top level `Makefile`.
Added `make social` to make the `social.html` page from `social.md`.

The `bin/gen-top-html.sh` now is able to process a argument of **social**
to process the new top level `social.html` page.

Changed `bin/gen-top-html.sh` VERSION from "2.0.0 2025-03-13"
to "2.0.1 2025-07-25".

Below `About -> Home page` a new `About -> IOCCC social media` menu item
as added.

Because the menu change touched every HTML file, we changed the general
copyright date range for HTML files from "1984-2024" to "1984-2025"
due to the extensive changes made for **IOCCC28**.

Those markdown files that were modified in 2025 had their copyright date
range also changed from "1984-2024" to "1984-2025".

Rebuilt tarballs and sitemap due to the extensive HTML rebuilding.

Ran `make update` to perform the above.
2025-07-26 13:06:29 -07:00

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<h1>The International Obfuscated C Code Contest</h1>
<h2>obfuscation.html for 2015/burton</h2>
</div>
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<h3 id="deobfuscation">Deobfuscation</h3>
<p><code>calc</code> is a recursive-descent parser. It allocates from the stack deep enough
that all expressions are exhausted before the recursion stack depth reaches the
allocations. The memory map and source is documented in
<a href="src.doc.txt">src.doc.txt</a>. Tokens are encoded using values 0-20, where 0 is an
invalid token, 1 is minus, 2 is space, 3 is plus, etc. The necessary constants
are derived at the start of the program, using the guarantee that globals are
initialized to zero; so a correct NULL pointer is obtained from an uninitialized
global pointer variable, and the integers from uninitialized global <code>int</code>
variables. If <code>x</code> is a global <code>int</code>, then <code>!x</code> is <code>1</code>, and the derivation
proceeds from there, using some identities that are confusingly similar and
interestingly combined (increasing obfuscation):</p>
<pre><code> obc clr
--- ---
-~x x+1
~-x x-1
y-~x y+x+1</code></pre>
<p>The derived constants are a compromise between simple expressions, maximum utility,
and minimum number of variables used.</p>
<p>Command line arguments are copied into the upper half of the input buffer,
separated by a space. This allows the code to have a single input parser by using
a pointer-to-func to either <code>getchar(3)</code> if live, or a <code>getchar(3)</code> simulator.</p>
<p>A small amount of obfuscation comes from <code>void</code> functions declared <code>int</code>, but
missing <code>return</code>. This is necessary to allow these functions in ternary <code>?:</code>
expressions and paired with <code>&amp;&amp;</code> and <code>||</code>; but the requisite returns would add
symbol count at no benefit to obscurity or functionality. Function
decomposition was mostly chosen to avoid curly braces: if a <code>for</code>-loop required
multiple statements, the body became a new function. Last, but not least:
sharing state via global variables is an ancient and honored form of
obfuscation, and remarkably effective.</p>
<hr style="width:10%;text-align:left;margin-left:0">
<p>Jump to: <a href="#">top</a></p>
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<div id="coda"><h3>Coda</h3>
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