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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta name="GENERATOR" content="mkd2html 2.1.5a DL=DISCOUNT">
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=utf-8">
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<link rel="stylesheet"
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type="text/css"
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href="../hint.css">
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<title>Best abuse of the rules</title>
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</head>
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<body>
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<h1>Best abuse of the rules</h1>
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<p>Dave Burton<br>
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<a href="http://ioccc.snox.net">http://ioccc.snox.net</a></p>
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<h2>Judges' comments:</h2>
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<h3>To use:</h3>
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<pre><code>make
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./prog [-tcksri] < file.c
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</code></pre>
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<h3>Try:</h3>
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<pre><code>./prog -i < prog.c
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./prog -s < prog.c
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./prog -sk < prog.c
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</code></pre>
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<p>If you get stuck, try:</p>
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<pre><code>make test
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</code></pre>
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<p>If you get really stuck, try:</p>
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<pre><code>man ./tac.man
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</code></pre>
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<h3>Selected Judges Remarks:</h3>
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<p>They say size isn’t everything, and in the case of IOCCC <a href="/2018/iocccsize.c">iocccsize.c</a>
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that is saying something! What is this program weighing and how much does it weigh?</p>
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<h2>Author’s comments:</h2>
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<h2>tac - tokenize and count C and derivative languages</h2>
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<blockquote><pre style="font-style:italic">
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tac computes C program size
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(obfuscated / otherwise)
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by splitting code as tokens small,
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ignoring space, then counting all.
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It tries quite hard to act the same
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as counting tool of I-OCCC fame.
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Some bugs were fixed, it's faster too,
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and does more things, just add some glue!
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It does far more than print the size:
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the token part's a better prize!
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With each upon on a single line,
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how many things can you design?
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Included is a keyword sorter,
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de-obfuscator, freq reporter.
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With code produced as little parts,
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just add your own creative arts.
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But first you have to figure out
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the braces part, without a doubt!
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And then the code - it isn't easy:
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for as else? That's rather cheesy!
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The rest of it is standard fare:
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expressions strange, the globals bare,
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confusing symbols one and oh,
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and precedence you have to know.
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The keyword list was made external,
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because of standards change eternal.
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Thus other languages can now,
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be counted just like C, somehow!
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I hope you find this code obscure
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enough to win, and thus procure
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a public place for all to see
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how badly I can butcher C!
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</pre></blockquote>
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<h2>Said another way….</h2>
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<p><code>tac</code> is the inverse of <code>cat</code>(1): it un-concatenates its input into C tokens,
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writing the token stream to stdout. There are options to suppress the token ids,
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summarize the token counts, and several options to allow it to be compatible
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with <code>iocccsize</code>.</p>
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<p>The token-based output is quite useful in analyzing source code (see below),
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and the counter is more accurate than <code>iocccsize</code> (see below); but this can be
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fixed by using the -c compatibility flag, restoring the following problems as
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in the official tool:</p>
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<ul>
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<li>whitespace <strong>within</strong> a string is <strong>not</strong> counted;
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this seems wrong, as these chars <strong>are</strong> significant</li>
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<li>“<code>{;}</code>” is not counted within a double-quoted string</li>
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<li>whitespace preceding a comment is char-counted, unless the comment starts a line</li>
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<li>-k processes the reserved words within <code>//</code> comments(!), but not <code>/*</code>, changing the counts</li>
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</ul>
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<p>The following bugs are always corrected:</p>
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<ul>
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<li>treats <code>/*/</code> as a complete comment (<code>/*/int if for/*/</code> has three keywords)</li>
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<li>-k enables <code>//*</code> or within a line comment <code>/*</code> to initiate a comment block until following <code>*/</code></li>
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<li>-k processes double quote characters in <code>//</code> comments -
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thus a solitary quote consumes everything until the next quote</li>
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<li>single quotes are not handled correctly (<code>'"'</code> starts a dquote in <code>iocccsize</code>)</li>
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<li><code>#ifndef</code> is omitted as a keyword (but <code>#ifdef</code> is allowed?)</li>
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<li>I is not a reserved word.</li>
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<li><code>tac</code> correctly penetrates <a href="http://ioccc.org/2014/birken/hint.html" title="Best use of port 1701">23rd century cloaking technology</a>. ;-)</li>
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</ul>
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<p>There is one (known) remaining problem with detection:</p>
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<ul>
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<li><p>comments between preprocessor hash and keyword are not replaced with whitespace;
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the following counts #include as two tokens, <code>#</code> and <code>include</code> (not as a reserved word):</p>
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<pre><code> #/*this will not be counted*/include/*correctly*/<stdio.h>
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</code></pre></li>
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</ul>
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<p>Fixing this properly hampers backwards compatibility in counting. This requires
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eliding comments during readsource (ISO 5.1.1.2, phase 3), and yet still
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counting words correctly absent -k.</p>
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<h2>Backwards Compatibility</h2>
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<p><code>tac</code> was run over all 366 previous IOCCC winning entries:</p>
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<pre><code>find ~/src/obc -type f -name \*.c | wc
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</code></pre>
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<p>The discrepancies found are documented and explained in the file “discrepancies”.</p>
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<pre><code>find ~/src/obc -type f -a -name "*.c" | xargs ./spotcheck ./prog | ./spotdiff |
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grep -v keep | diff -bw - discrep* | grep "[<>] cl "
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</code></pre>
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<p>In summary, there are only 6 unique entries out of 366 that have any variation
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in Rule 2 counts; in all cases, the differences are due to bugs within
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<code>iocccsize</code>, described in detail in the file <code>discrepancies</code>. There are only 40
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files (40/366, ~11%, including originals and variations) that differ at all, 31
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only in word count; most word count differences appear related to comment block
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detection, weighted more towards recent entries (2011 and onward = 20/40 ~50%).</p>
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<p>This (minor) variation in word count values has not been addressed since
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it is not a qualifying metric, nor is it very useful in a programming context:
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whitespace surrounds English words, not necessarily C tokens, as in <code>a+=1;</code>.</p>
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<p>Accuracy (versus compatibility) is demonstrated through a series of small test cases
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designed to allow exhaustive, hand-counted values for comparison with the tool values.
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These test cases were vital in debugging and regression testing, and provided a way to
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determine which tool was correct when there were differences.</p>
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<blockquote><p>A version of this tool in more clearly written C (tac.c)
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is presented for the Judge’s consideration as a more accurate replacement for <code>iocccsize</code>.
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This obfuscated entry is derived from (and compatible with) that code,
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but due to obfuscation, has had some significant, deep changes for the contest.
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Nevertheless, the more clearly written code remains a spoiler for this entry.</p></blockquote>
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<p>NB: <code>iocccsize</code> gets a different answer from <code>tac</code> on its own (iocccsize.c) source code;
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<code>tac</code> gets the correct answer. This is due to the aforementioned bugs within <code>iocccsize</code>,
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proved by fixing iocccsize.c with the included patch, so <code>iocccsize</code> reports
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the correct answer for itself.</p>
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<h2>But wait… There’s More!</h2>
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<p>There is no limit on line length, file length, comment length, or identifier length.</p>
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<p><code>tac</code> features an accurate tokenizer; which presents each C token on a line by itself.
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This feature enables interesting analyses of C (and C++) code, hard to get any other way.</p>
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<p>For instance, here is a simple token counter, useful in finding repeated long tokens, or operator
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frequency, or counting the references to identifiers, constants, or breadth of use of the
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language:</p>
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<pre><code>!/bin/sh
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cat $* | ./prog -t | sort | uniq -c | sort -k1nr
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</code></pre>
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<p>And here is a C keyword frequency counter:</p>
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<pre><code>#!/bin/sh
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function iskeyword {
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awk 'BEGIN{f="c11";while(getline<f)k[$1]=0}
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{if($1 in k)k[$1]++}END{for(i in k)print k[i],i}'
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}
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cat $* | ./prog -t | iskeyword | sort -k1nr
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</code></pre>
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<p>This script was used to “optimize” the reserved word order so the most frequent IOCCC
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winning entry keywords are checked first.</p>
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<blockquote><p>An interesting aside: as might be expected, obfuscation has changed the frequency of
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keyword distribution over time. The top five for the decades:</p>
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<pre><code> 1980s 1990s 2000s 2010s
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----- ----- ----- -----
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94 if 532 char 375 if 254 int
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69 for 524 if 372 char 217 for
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59 while 417 int 332 int 198 if
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48 char 223 for 184 for 121 return
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43 int 223 void 165 return 104 char
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</code></pre></blockquote>
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<p>The keyword list is external to the program, and is easily changed, sorted, checked, verified.
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This allows such additional programs in concert with the tool’s primary operation.</p>
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<p>A poor-man’s de-obfuscator can be based upon the output of <code>tac -t</code> and a handful of
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simple rules (and another use of the external keyword file).
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A more refined version of this is included in the file <code>unob.sh</code>,
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but the simple code below is a serviceable obfuscated C de-obfuscator in a <em>scripting language</em>.
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It really is this easy with <code>tac</code>:</p>
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<pre><code>#!/bin/sh
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script='
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BEGIN {
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last=nl="\n";
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f="c11"; while(getline <f > 0) kw[$0]++; close(f);
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}
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function iskw(a) { return a in kw }
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function indent(a) { return sprintf("%*s", n*3, " ") }
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function newline() { if (!infor && last != nl) printf last=nl; }
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function show(a) {
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if (last==nl) printf "%s", indent()
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printf "%s%s", space(), a
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last=a
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}
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function space() {
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return iskw(last) ||
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(last ~ /[A-Za-z0-9_+-\/%^[&\]\)=:<>;]$/ && $0 !~ /[:;()\[\],]/) ? " " : ""
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}
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/^\(/ { ++paren }
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/^\)/ { --paren }
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/^for/ { newline(); infor=1 }
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infor && /^;/ { ++infor; show($0 " "); next }
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infor==1 && /^:/ { ++infor }
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infor>1 && paren==0 { infor=0 }
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/^\?/ { tern++; n++; newline(); show($0 " "); next }
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tern && /^:/ { newline(); show($0); --tern; --n; next }
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/^#/ { newline(); show($0); newline(); next }
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/^;/ { show($0); newline(); next }
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/^{/ { show($0); ++n; newline(); next }
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/^}/ { n--; newline(); show($0); newline(); next }
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{ show($0) }
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'
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cat $* | sed 's/#include/##include/' | cpp -E -trigraphs |
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sed 's/^# .*$//' | sed 's/^#//' |
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./prog -t | awk "$script"
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</code></pre>
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<h2>On the question of obfuscation</h2>
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<ul>
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<li><p>I assume you noticed the <a href="https://www.youtube.com/watch?v=fUspLVStPbk&start=53" title="Meaning of Life">braces</a>?</p>
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<p><em>Every brace is sacred,<br>
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Every brace is great.<br>
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If a brace is wasted,<br>
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Clang gets quite irate</em>.</p></li>
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<li><p>Keywords follow the 2010s top five, without the <code>if</code>, for interesting flow control.</p></li>
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<li>Sometimes a <code>for</code> can be an <code>else</code> - <a href="https://www.youtube.com/watch?v=OHVjs4aobqs" title="Inconceivable">inconceivable</a>!</li>
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<li>I see the <code>getopt</code>. But “<a href="https://www.youtube.com/watch?v=Ug75diEyiA0" title="Where's the beef?">where’s the beef?</a>”</li>
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<li><p>No character constants, several int constants, and one string
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(hint: which does not encode letters) – how does this code parse code?</p>
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<blockquote><p>Interesting aside: how many is “several int constants”?</p>
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<pre><code> ./prog < prog.c 2>/dev/null | awk '$1~/260/{a[$2]++}END{for(i in a)print i,a[i]}'
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... | wc
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</code></pre>
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<p>Which numbers are most often used?</p>
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|
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<pre><code> ... | sort -k2nr | sed 5q
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</code></pre></blockquote></li>
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<li><p>The code describes its function by careful arrangement of variables up front…</p></li>
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<li>…coupled with a description of the typical IOCCC contestant, or at least the author</li>
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<li>Why shouldn’t trigraph parsing be written in trigraph?</li>
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<li>Where iocccsize.c mocks, this code flaunts:
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“<em>no matter how well you may think you understand this code, you don’t, so don’t mess with it. :-)</em>”</li>
|
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<li><code>O,0,l,1</code> are used to confusing effect, local names obscure global names.</li>
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<li>Globals are used to pass information between routines: don’t reorder “unrelated” statements….</li>
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<li>How does the compatibility mode account for the fundamentally different manner of computation?</li>
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<li>The algorithm is quite efficient; reserved word detection and trigraph parsing particularly so.</li>
|
||||
<li>This may be the first obfuscated submission that provides the means for its own de-obfuscation.</li>
|
||||
</ul>
|
||||
|
||||
|
||||
<h2>Rule 2</h2>
|
||||
|
||||
<p>The keyword list is externalized as an include file. This presents a useful
|
||||
feature for the source code: not only can the reserved word script above be
|
||||
produced, but the tool can be rebuilt with any set of reserved words, just by
|
||||
using a different list. For instance: removing all the secondary keywords;
|
||||
removing all the C11 keywords; trying just K&R C. Since C++ and Java share the
|
||||
same operators as C, just change the keyword list and <code>tac</code> will correctly
|
||||
tokenize both of these; the tokens >>> and :: can be handled with a short
|
||||
post-filter (tokenfix, included).</p>
|
||||
|
||||
<p>I believe this entry may also satisfy the request for gratuitous use of all the C11 keywords?
|
||||
Whether this context satisfies “intended C language context” is a matter of interpretation. ;-)
|
||||
And <code>tac</code> is ready for the IOCCC++ contest. And the IOJCC trashcan.</p>
|
||||
|
||||
<p>The following reserved word files are included:</p>
|
||||
|
||||
<pre><code>kandr from my venerable 1978 18th printing "The C Programming Language"
|
||||
v7unix 7th edition Unix source code, extracted from c00.c
|
||||
kandr2 from my 1988 1st printing "The C Programming Language", 2e
|
||||
ansi ANS X3.159-1989
|
||||
c99 ISO/IEC 9899:1999(E)
|
||||
c11 ISO/IEC 9899:201x(E) N1570
|
||||
c++98 http://en.cppreference.com/w/cpp/keyword
|
||||
c++11 ISO/IEC 14882:2011(E) N3337 2012-01-16
|
||||
c++14 ISO/IEC 14882:2014(E) N4296 2014-11-09
|
||||
java8 http://docs.oracle.com/javase/specs/index.html
|
||||
ioccc.kw.freq c11 + additional words, sorted on frequency of occurrence in ioccc winners
|
||||
</code></pre>
|
||||
|
||||
<p>NB: The keyword file used in this code is derived from the list in iocccsize.c,
|
||||
which is neither complete (<code>#define</code>, <code>#ifndef</code>, <code>#undef</code> are missing
|
||||
– yes, Virginia knows about <code>#define</code> omitted on purpose),
|
||||
nor correct (many more are added: <code>I</code>, <code>true</code>, <code>bool</code>, <code>compl</code>, …):</p>
|
||||
|
||||
<pre><code>(sed -n '1p' c11; sed -n '2,$p' ioccc.kw.freq | sort) | comm -3 - c11
|
||||
</code></pre>
|
||||
|
||||
<p>That is an obfuscated way to say “diff”. But it also more clearly shows the, um, diffs.</p>
|
||||
|
||||
<p>The usage string is similarly externalized, providing a better usability string than
|
||||
the limits would otherwise allow. If this is considered bending the rules too far,
|
||||
just -DU=O to get a passible, if cryptic, usage message using no additional octets
|
||||
than without the define.
|
||||
This also allows the builder to configure the amount of help a utility should provide
|
||||
(<a href="https://www.youtube.com/watch?v=VU0GYSA1POs" title="Ants">you want a manpage? Because that’s how you get a manpage.</a>)
|
||||
– a rather significant point of contention made moot.</p>
|
||||
|
||||
<p>There is definitely abuse of the Rule2 counter, exploiting a “feature” of <code>iocccsize</code>:
|
||||
<code>iocccsize</code> does not Rule2 count {, } and ; when followed by whitespace – even within a string!
|
||||
Thus: Freecode, a simple, uncounted, highly obfuscated encoding of a central part
|
||||
of this program. (The reserved word list is not Freecoded, both because it is useful
|
||||
apart from the program, and because Freecode is not entirely free.*)</p>
|
||||
|
||||
<ul>
|
||||
<li>Some restrictions apply. Not approved for all uses. Some assembly required.</li>
|
||||
</ul>
|
||||
|
||||
|
||||
<h2>Compilation</h2>
|
||||
|
||||
<p>The code is ANSI compliant, but it does have a string longer than 509 characters.
|
||||
It has been tested on OSX and Linux, Clang and GCC.</p>
|
||||
|
||||
<p>The code uses trigraphs, ironically: it parses trigraphs with trigraph code.
|
||||
Because that’s funny. And it remains obscure after, so trigraphs are not used for obfuscation.
|
||||
Thus -trigraphs -Wno-trigraphs (which is also humorous).</p>
|
||||
|
||||
<p>It’s obfuscated C. Thus -Wno-parentheses -Wno-empty-body -Wno-char-subscripts.</p>
|
||||
|
||||
<p>The code uses unsigned chars, but C strings are signed. Thus -Wno-pointer-sign.
|
||||
NB: This is <em>not</em> a portability concern, the one string holds only printable ASCII characters.</p>
|
||||
|
||||
<p>Thus:</p>
|
||||
|
||||
<pre><code>clang -ansi -Wall -trigraphs -Wno-trigraphs -Wno-parentheses -Wno-empty-body -Wno-char-subscripts -Wno-pointer-sign -DU=O -DW=\"keywords\" -o prog prog.c
|
||||
</code></pre>
|
||||
|
||||
<h2>Coda</h2>
|
||||
|
||||
<p>Cody Ferguson was relentless in his pursuit of bugs.
|
||||
Thanks to his reports, the version of <code>unob.sh</code> is stronger,
|
||||
<code>tac</code> groks digraphs, <code>tokenfix</code> corrects for missing digraphs in <code>prog.c</code>,
|
||||
and the program <code>manpage</code> was added to the corpus.</p>
|
||||
|
||||
<p><code>manpage</code> is a useful program that turns ASCII versions of man pages (e.g. <code>tac.man</code>) into real
|
||||
man pages. It works for C and C-like languages, command lines,
|
||||
and was designed to handle man page sections 1-8.
|
||||
It works well on most inputs, but tends to need some raw nroff for more fancy constructions,
|
||||
such as combined arguments
|
||||
(e.g. the -r and -s arguments to tac are not recognised when written as -rs in prose).</p>
|
||||
|
||||
<p>Try:</p>
|
||||
|
||||
<pre><code>manpage tac
|
||||
|
||||
manpage -h
|
||||
manpage -h | manpage
|
||||
manpage -h | manpage -R | less
|
||||
manpage -h | manpage -P | lpr
|
||||
</code></pre>
|
||||
|
||||
<hr />
|
||||
|
||||
<TABLE><TR>
|
||||
<TD><a rel="license" href="http://creativecommons.org/licenses/by-sa/3.0/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by-sa/3.0/88x31.png" /></a></TD>
|
||||
<TD><P>© Copyright 1984-2018,
|
||||
<A HREF="/judges.html">Leo Broukhis, Simon Cooper, Landon Curt Noll</A>
|
||||
- All rights reserved<BR>
|
||||
This work is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-sa/3.0/">Creative Commons Attribution-ShareAlike 3.0 Unported License</a>.</P></TD>
|
||||
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|
||||
</TR></TABLE>
|
||||
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|
||||
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|
||||
Reference in new issue
Block a user