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  <h1>The International Obfuscated C Code Contest</h1>
  <h2>2015/howe - Most Different</h2>
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  <a class="Left" href="../hou/index.html">&larr; hou</a>
  <a class="Left" href="../index.html">&uarr; 2015 &uarr;</a>
  <a class="Left" href="../mills1/index.html">mills1 &rarr;</a>
  <a class="Right" href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/prog.c">C code</a>
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<h2 id="author">Author:</h2>
<ul>
<li>Name: <a href="../../authors.html#Anthony_C_Howe">Anthony C. Howe</a><br>
Location: <a href="../../location.html#CA">CA</a> - <em>Canada</em></li>
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<h2 id="to-build">To build:</h2>
<pre><code>    make</code></pre>
<p>There is an alternate version provided. See <a href="#alternate-code">Alternate code</a>
below.</p>
<h2 id="to-use">To use:</h2>
<pre><code>    ./prog file1 file2

    ./prog -d file1 file2</code></pre>
<h2 id="try">Try:</h2>
<pre><code>    ./try.sh</code></pre>
<h2 id="alternate-code">Alternate code:</h2>
<p>This alternate version does not use a 64-bit FNV hash. This was the original
entry but was changed to be the alt version.</p>
<h3 id="alternate-build">Alternate build:</h3>
<pre><code>    make alt</code></pre>
<h3 id="alternate-use">Alternate use:</h3>
<p>Use <code>prog.alt</code> as you would <code>prog</code> above.</p>
<h2 id="judges-remarks">Judges’ remarks:</h2>
<p>This is the best use of the FNV that we have seen in the IOCCC so far!
The output, when used without <code>-d</code>, is compatible with POSIX <code>diff(1)</code> and
is suitable for use with <code>patch(1)</code>.</p>
<p>We welcome back Canada to the list of nations from where winning
entries have been submitted.</p>
<p>Is this code a bug or a feature? :-) Or is this an attempt to corrupt the
programming of our youth? Should we heed Kyle’s mom words that she uttered
during a South Park P.T.A. Meeting?</p>
<p>“We must stop dirty (C) language from getting to our children’s ears!”</p>
<p><a href="https://www.youtube.com/watch?v=bOR38552MJA">Blame Canada</a></p>
<p>Or should we teach our youth to understand the intricacies of this code?
Ying Tong Iddle I Po! We suggest you read the source for yourself, which
might be easier than the academic papers it was inspired by.</p>
<p>NOTE: Unlike the original entry source, <a href="prog.alt.c">prog.alt.c</a>,
<a href="prog.c">prog.c</a> uses a
64 bit FNV hash and fixes a function call warning.</p>
<h2 id="authors-remarks">Author’s remarks:</h2>
<h3 id="features">Features</h3>
<ul>
<li><p>“An O(NP) Sequence Comparison Algorithm” by Wu, Manber, Myers, Miller.</p></li>
<li><p>Output compatible with <code>patch(1)</code>.</p></li>
<li><p>Strokes one of the judge’s ego (I couldn’t email chocolate or curry).</p></li>
</ul>
<h3 id="description">Description</h3>
<p>This is a functioning micro <code>diff(1)</code> tool using an <a href="http://myerslab.mpi-cbg.de/wp-content/uploads/2014/06/np_diff.pdf">O(NP) algorithm</a>,
compared to the older <a href="http://www.xmailserver.org/diff2.pdf">O(ND) difference algorithm</a> used by some versions
of <code>diff(1)</code>. Its output is based on the default <code>diff(1)</code> output described by POSIX
and <a href="http://pubs.opengroup.org/onlinepubs/9699919799/utilities/diff.html">the Open Group Base Specifications</a>. The output is suitable for use
with <code>patch(1)</code>.</p>
<p>The <code>-d</code> option simply writes the edit distance between <code>file1</code> and <code>file2</code>.</p>
<h3 id="observations">Observations</h3>
<p>The FNV1a hash is a little slow compared to the trivial hash <a href="https://www.gnu.org/software/diffutils/">GNU
diff</a> uses. I downloaded a plain text
copy of “War And Peace” from <a href="https://www.gutenberg.org">Project Gutenberg</a>,
used <a href="makeholes.c">makeholes.c</a> to make 1000 random changes, then profiled and
timed the program verses GNU <code>diff(1)</code>. The bottleneck appears to be in the
file I/O and line hashing with an average +0.05s slower. Using a huge file like
“War And Peace” for testing offsets the <code>diff(1)</code> optimised file I/O.</p>
<p>There is no hash collision checking, partly because FNV1a appears to generate
very <a href="http://programmers.stackexchange.com/questions/49550/which-hashing-algorithm-is-best-for-uniqueness-and-speed">few collisions</a> and an assumption that localised collisions within
a region of edits are highly unlikely.</p>
<h3 id="support-files">Support Files</h3>
<ul>
<li><p><a href="prog-test.sh">prog-test.sh</a>
Basic test program verifies known test edit distances and <code>patch(1)</code> support.</p></li>
<li><p><a href="avgtime.sh">avgtime.sh</a></p></li>
<li><p><a href="makeholes.c">makeholes.c</a>
Random edits (holes) made to a file in-place.</p></li>
</ul>
<h3 id="references">References</h3>
<p>Wu, Manber, Myers, and Miller; August 1989;<br>
“An O(NP) Sequence Comparison Algorithm”;<br>
<a href="http://myerslab.mpi-cbg.de/wp-content/uploads/2014/06/np_diff.pdf" class="uri">http://myerslab.mpi-cbg.de/wp-content/uploads/2014/06/np_diff.pdf</a></p>
<p>Fowler, Noll, Vo; 1994<br>
<a href="http://www.isthe.com/chongo/tech/comp/fnv/index.html" class="uri">http://www.isthe.com/chongo/tech/comp/fnv/index.html</a></p>
<p>Fowler, Noll, Vo on Wikipedia<br>
<a href="https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function" class="uri">https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function</a></p>
<p>“diff”, The Open Group Base Specifications Issue 7<br>
IEEE Std 1003.1, 2013 Edition<br>
<a href="http://pubs.opengroup.org/onlinepubs/9699919799/utilities/diff.html" class="uri">http://pubs.opengroup.org/onlinepubs/9699919799/utilities/diff.html</a></p>
<p>Eugene W. Myers; “An O(ND) Difference Algorithm and Its Variations”;<br>
Algorithmica, 1986, pages. 251-266<br>
<a href="http://www.xmailserver.org/diff2.pdf" class="uri">http://www.xmailserver.org/diff2.pdf</a></p>
<p>Webb Miller and Eugene W. Myers; “A File Comparison Program”;<br>
Software-Practice And Experience, Vol. 15(11). 1025-1040 (November 1985)<br>
<a href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.189.70&amp;rep=rep1&amp;type=pdf" class="uri">http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.189.70&amp;rep=rep1&amp;type=pdf</a></p>
<p>D.S. Hirschberg, “A linear space algorithm for computing maximal common subsequence problem”;<br>
Comm. of ACM, Vol. 18, June 1975, pages 341-343<br>
<a href="http://www.mathcs.emory.edu/~cheung/Courses/323/Syllabus/DynProg/Docs/Hirschberg-LCS-1975.pdf" class="uri">http://www.mathcs.emory.edu/~cheung/Courses/323/Syllabus/DynProg/Docs/Hirschberg-LCS-1975.pdf</a></p>
<p>Which hashing algorithm is best for uniqueness and speed?<br>
<a href="http://programmers.stackexchange.com/questions/49550/which-hashing-algorithm-is-best-for-uniqueness-and-speed" class="uri">http://programmers.stackexchange.com/questions/49550/which-hashing-algorithm-is-best-for-uniqueness-and-speed</a></p>
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<h1 id="inventory-for-2015howe">Inventory for 2015/howe</h1>
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<h2 id="primary-files">Primary files</h2>
<ul>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/prog.c">prog.c</a> - entry source</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/Makefile">Makefile</a> - entry Makefile</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/prog.alt.c">prog.alt.c</a> - alternative source</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/prog.orig.c">prog.orig.c</a> - original source</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/avgtime.sh">avgtime.sh</a> - how to run</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/makeholes.c">makeholes.c</a> - add random holes to a file</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/prog-test.sh">prog-test.sh</a> - how to run</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/try.sh">try.sh</a> - how to run</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/cc.1">cc.1</a> - gcc man page</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/spoiler/Makefile">spoiler/Makefile</a> - SPOILER WARNING how to make the spoiler</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/spoiler/err.h">spoiler/err.h</a> - SPOILER WARNING</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/spoiler/prog.c">spoiler/prog.c</a> - SPOILER WARNING</li>
<li><a href="war-and-peace.txt">war-and-peace.txt</a> - War and Peace translated to English</li>
</ul>
<h2 id="secondary-files">Secondary files</h2>
<ul>
<li><a href="2015_howe.tar.bz2">2015_howe.tar.bz2</a> - download entry tarball</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/README.md">README.md</a> - markdown source for this web page</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/.entry.json">.entry.json</a> - description of entry in JSON</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/.gitignore">.gitignore</a> - list of files that should not be committed under git</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/howe/.path">.path</a> - directory path from top directory</li>
<li><a href="index.html">index.html</a> - this web page</li>
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