Files
Landon Curt Noll a1c86c8a7a add original C links to entry navigation bars
The navigation bar for a winning entry now has a "_Original C_" link
(between the ✅ and the Inventory on the right hand side) so that one
may easily view the original C code that was submitted for IOCCC judging.

Ran `make www timestamp` to perform the above.
2025-08-10 12:46:23 -07:00

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<h1>The International Obfuscated C Code Contest</h1>
<h2>2004/omoikane - Best utility</h2>
<h3>A CRC inserter</h3>
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<div class="navbar">
<a class="Left" href="../newbern/index.html">&larr; 2004/newbern</a>
<a class="Left" href="../index.html">&uarr; 2004 &uarr;</a>
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<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/2004/omoikane/omoikane.c">C code</a>
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<h2 id="author">Author:</h2>
<ul>
<li>Name: <a href="../../authors.html#Don_Yang">Don Yang</a><br>
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</code></pre>
<h2 id="to-use">To use:</h2>
<pre><code> ./omoikane infile layout outfile</code></pre>
<h2 id="try">Try:</h2>
<pre><code> ./try.sh</code></pre>
<h2 id="judges-remarks">Judges’ remarks:</h2>
<p>For extra credit, spot the checksum in the source file itself.
What makes this one particularly interesting is that the checksum,
strictly speaking, isn’t being computed at all. Rather, the file
is modified to have the desired checksum! This does, we suppose,
solve the problem that inserting a checksum would change the file’s
checksum; if you have to change it, you might as well change it!</p>
<p>This program was submitted under the name <code>Rinia</code>, so the <a href="#authors-remarks">Author’s
remarks</a> refer to it as such.</p>
<h2 id="authors-remarks">Author’s remarks:</h2>
<h3 id="rinia-11404"><code>Rinia</code> (1/14/04)</h3>
<p><code>Rinia</code> is a tool for embedding CRCs in text files. No need to assign
strange file names or package .SFVs with your files! <code>Rinia</code> will
insert a human-readable checksum string in the text itself! <code>^_^</code></p>
<h3 id="usage">Usage</h3>
<pre><code> ./omoikane &lt;infile&gt; &lt;layout&gt; &lt;outfile&gt;</code></pre>
<p>All three arguments may reference the same file. All files is
assumed to be of ASCII character set.</p>
<h3 id="input">Input</h3>
<p>Any file larger than 8 bytes is valid. Upper limit on file size is
limited by memory.</p>
<p>If input file can’t be loaded for any reason, <code>Rinia</code> will say “bad
input” and exit immediately.</p>
<h3 id="layout">Layout</h3>
<p>The layout file contains a map of where <code>Rinia</code> can patch. The
content consists of marker characters (where <code>Rinia</code> is allowed to
change in the original text) and other characters (where the
original text will stay as is). <code>Rinia</code> will select the marker
character using these heuristics:</p>
<ol type="1">
<li>Ignore all space/control/extended characters.</li>
<li>Select characters that appeared 8 times in a row.</li>
<li>Of those selected characters, pick one with the lowest
frequency.</li>
</ol>
<p>One way to create the layout file is to make a copy of the original
file, replace where you want <code>Rinia</code> to match with a rare character,
then replace the remaining ones with space. Often it’s possible to
write the original file in such a way that it can be used as a
layout.</p>
<p>Example file/layout:</p>
<pre><code> file: layout:
crc = ######## ... . XXXXXXXX
patch = ###### ..... . XXXXXX
other text here ..... .... ....</code></pre>
<p>And <code>Rinia</code> may generate a file similar to this:</p>
<pre><code> crc = 1bad73cf
patch = #FR-QQ
other text here</code></pre>
<p>Note that the original file by itself is a valid layout file, since
<code>Rinia</code> will recognize that only <code>#</code> marks enough space to hold the
checksum, and has the lowest frequency.</p>
<p>If layout file can’t be used for any reason, <code>Rinia</code> will say “bad
layout” and exit immediately.</p>
<h3 id="output-m">Output m</h3>
<p>If <code>Rinia</code> finds a usable checksum, she will say “OK.” and write to
the specified output file. Otherwise the exit message is “fail”
and nothing is written.</p>
<p>Chances of success and how long it takes to run to completion is
completely dominated by the layout file design. In general, <code>Rinia</code>
runs faster if the checksum is placed before the other marker
characters rather than after, e.g.:</p>
<pre><code> a: X X XXX b: XXXXXXXX c: XXXXXXXX
XXXXXXXX X X XXX XXXXX</code></pre>
<p><code>a</code> usually takes the longest time, while <code>c</code> usually is the
fastest.</p>
<p>That said, each run is randomized with respect to system time, so
it’s not always certain whether <code>Rinia</code> will succeed in a short time
or not. In general, 5 marker characters are sufficient, and takes
a few minutes.</p>
<p>For reference, <code>rinia.c</code> was produced on a 1.7GHz machine (the
checksum is at line 17). Out of 25 runs, the shortest was 2
seconds while the longest took 5 minutes. Average was about a
minute. Checksum for this file (<code>b7a81524</code>) took about 4 minutes.</p>
<h3 id="algorithm">Algorithm</h3>
<p>Inserting a checksum in the file you are computing the checksum of
isn’t quite trivial, since changing the file content would change
the final checksum value.</p>
<p>To insert the checksum, <code>Rinia</code> first assumes a random final
checksum, inserts that string, then modifies other parts to compensate
for the change in content.</p>
<p>The compensation bytes are very easy to compute for binary files
with enough consecutive scratch areas, but for text files with
non-consecutive areas and limited degrees of freedom, <code>Rinia</code> has to
try out all character combinations. This is done in a hierarchical
fashion, computing only smallest partial checksum after each
change.</p>
<p>For computers a few years old, this is probably still too slow to be
acceptable… but at the speed the IOCCC judges run the contest
these days, I am sure you have enough patience for it <code>_^</code></p>
<h3 id="source-code">Source code</h3>
<p><code>rinia.c</code> should compile anywhere (but with a few warnings). I don’t
have a big-endian machine to test but <code>Rinia</code> should work there as
well. ASCII character set required though.</p>
<p>Code is formatted to the shape of “<code>Rinia</code>” from the anime/game
“Moekko Company”. Of course at 90x50 it’s hard to recognize anything
<code>^_^</code></p>
<p><code>Rinia</code> is the slow but hardworking android. On some jobs she does
very well, on others she would spend lots of time and effort but
still fail…</p>
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<h1 id="inventory-for-2004omoikane">Inventory for 2004/omoikane</h1>
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<h2 id="primary-files">Primary files</h2>
<ul>
<li><a href="https://github.com/ioccc-src/winner/blob/master/2004/omoikane/omoikane.c">omoikane.c</a> - entry source code</li>
<li><a href="https://github.com/ioccc-src/winner/blob/master/2004/omoikane/Makefile">Makefile</a> - entry Makefile</li>
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<li><a href="https://github.com/ioccc-src/winner/blob/master/2004/omoikane/omoikane.info">omoikane.info</a> - information about Rinia - author’s name for program</li>
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