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Landon Curt Noll a1c86c8a7a add original C links to entry navigation bars
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<h1>The International Obfuscated C Code Contest</h1>
<h2>2020/burton - Best one liner</h2>
<h3>Byte to binary without loops as a 1-liner</h3>
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<a class="Left" href="../../2019/yang/index.html">&larr; 2019/yang</a>
<a class="Left" href="../index.html">&uarr; 2020 &uarr;</a>
<a class="Left" href="../carlini/index.html">2020/carlini &rarr;</a>
<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/2020/burton/prog.c">C code</a>
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<h2 id="author">Author:</h2>
<ul>
<li>Name: <a href="../../authors.html#Dave_Burton">Dave Burton</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>
<h3 id="bugs-and-misfeatures">Bugs and (Mis)features:</h3>
<p>The current status of this entry is:</p>
<blockquote>
<p><strong>STATUS: INABIAF - please DO NOT fix</strong></p>
</blockquote>
<p>For more detailed information see <a href="../../bugs.html#2020_burton">2020/burton in bugs.html</a>.</p>
<h2 id="to-use">To use:</h2>
<pre><code> ./prog arg ...</code></pre>
<h2 id="try">Try:</h2>
<pre><code> ./try.sh</code></pre>
<h2 id="alternate-code">Alternate code:</h2>
<p>By default, the program works for Little Endian machines. This alternate build
is for Big Endian machines (that works whether you have LE or BE).</p>
<h3 id="alternate-build">Alternate build:</h3>
<p>Running <code>make</code> builds the alternate code by default.</p>
<h3 id="alternate-use">Alternate use:</h3>
<p>Use <code>prog_be</code> as you would <code>prog</code> above.</p>
<h2 id="judges-remarks">Judges’ remarks:</h2>
<p>Can you determine why this shows strange output for <code>./prog 128 128</code>
and <code>./prog 128 128 128 128</code> but not <code>./prog 128 128 128</code>?</p>
<p>Can you find a pattern here?</p>
<p>What happens if you specify different numbers?</p>
<p>This tiny one-liner is a bit-twiddler’s delight! It does all of the work
without looping.</p>
<p>To understand how it works, a good place to start is to look at the hex
value that results when the two magic constants are <code>XOR</code>ed.</p>
<p>Once you’ve figured out what happens with one set of constants, how can
choosing new constants, but using the same computation generate a reversed
result?</p>
<p>This code may be tested by:</p>
<pre><code> make test</code></pre>
<h2 id="authors-remarks">Author’s remarks:</h2>
<p>Invoke this with a single non-negative integer less than 256, and a useful
transformation occurs.</p>
<h3 id="rule-2-ish">Rule 2-ish:</h3>
<p>Exporting the constants <code>B</code>,<code>I</code>,<code>T</code>,<code>S</code> to the <a href="https://github.com/ioccc-src/winner/blob/master/2020/burton/Makefile">Makefile</a> allows the
code to be compiled for either LE (little-endian) or BE (big-endian)
machines(!!), so they are truly configuration parameters, not logic.</p>
<h3 id="notes">Notes:</h3>
<p>One <del>ping</del> argument only. It will segfault on zero arguments, and
display strange results with more than one argument.</p>
<p>Small, non-negative integers only. Useful range is <code>0 .. 511</code>, sorta, for LE; <code>0 .. 255</code> for BE. Bonus points if you can explain why the limits work this way.</p>
<p>ASCII character set, 64-bit <code>long long</code>s are required.</p>
<p>v,a,r,i,a,b,l,e,s_NAME the operation.</p>
<p>No loops, no branches?!?</p>
<h4 id="compilation">Compilation:</h4>
<p>Compiles cleanly under <code>clang -Wall -Weverything -pedantic</code>, but you need to add
<code>--include stdio.h --include stdlib.h</code> for the <code>printf(3)</code> and <code>atoi(3)</code>.</p>
<p>On a little-endian machine:</p>
<pre><code> clang -include stdio.h -include stdlib.h -Wall -Weverything -pedantic -DB=6945503773712347754LL -DI=5859838231191962459LL -DT=0 -DS=7 -o prog prog.c</code></pre>
<p>On a big-endian machine:</p>
<pre><code> clang -include stdio.h -include stdlib.h -Wall -Weverything -pedantic -DB=7091606191627001958LL -DI=6006468689561538903LL -DT=1 -DS=0 -o prog_be prog.c</code></pre>
<p>You might be interested to compile it both ways on the same host, and try:</p>
<pre><code> ./prog 1; ./prog_be 1</code></pre>
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<h2 id="primary-files">Primary files</h2>
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