From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <3e1162e60712190715q3f50d601sd88b1e0c6c74afc8@mail.gmail.com>
Date: Wed, 19 Dec 2007 07:15:09 -0800
From: "David Leimbach" <leimy2k@gmail.com>
To: 9fans@cse.psu.edu
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Subject: [9fans] fun and scary evil C code
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I was amused by this:
http://www.steike.com/code/useless/evil-c/

I particularly liked the "internalEndianMagic".

I see this in some XML libs, as well as GMP and other open sourced code.

http://unix.derkeiler.com/Newsgroups/comp.unix.programmer/2005-12/msg00198.html


From:
https://svn.r-project.org/R/trunk/src/extra/trio/trionan.c

/*
 * Endian-agnostic indexing macro.
 *
 * The value of internalEndianMagic, when converted into a 64-bit
 * integer, becomes 0x0706050403020100 (we could have used a 64-bit
 * integer value instead of a double, but not all platforms supports
 * that type). The value is automatically encoded with the correct
 * endianess by the compiler, which means that we can support any
 * kind of endianess. The individual bytes are then used as an index
 * for the IEEE 754 bit-patterns and masks.
 */
#define TRIO_DOUBLE_INDEX(x) (((unsigned char *)&internalEndianMagic)[7-(x)])
static TRIO_CONST double internalEndianMagic = 7.949928895127363e-275;
#endif

pretty weird stuff.

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I was amused by this:<div><br class="webkit-block-placeholder"></div><div><a href="http://www.steike.com/code/useless/evil-c/">http://www.steike.com/code/useless/evil-c/</a><br class="webkit-block-placeholder"></div><div><br class="webkit-block-placeholder">
</div><div>I particularly liked the &quot;internalEndianMagic&quot;.</div><div><br class="webkit-block-placeholder"></div><div>I see this in some XML libs, as well as GMP and other open sourced code.</div><div><br class="webkit-block-placeholder">
</div><div><a href="http://unix.derkeiler.com/Newsgroups/comp.unix.programmer/2005-12/msg00198.html">http://unix.derkeiler.com/Newsgroups/comp.unix.programmer/2005-12/msg00198.html</a>&nbsp;<br></div><div><br class="webkit-block-placeholder">
</div><div>From:</div><div><a href="https://svn.r-project.org/R/trunk/src/extra/trio/trionan.c">https://svn.r-project.org/R/trunk/src/extra/trio/trionan.c</a><br class="webkit-block-placeholder"></div><div><span class="Apple-style-span" style="font-family: Times; font-size: 16px; ">
<pre style="word-wrap: break-word; white-space: pre-wrap; ">/*
 * Endian-agnostic indexing macro.
 *
 * The value of internalEndianMagic, when converted into a 64-bit
 * integer, becomes 0x0706050403020100 (we could have used a 64-bit
 * integer value instead of a double, but not all platforms supports
 * that type). The value is automatically encoded with the correct
 * endianess by the compiler, which means that we can support any
 * kind of endianess. The individual bytes are then used as an index
 * for the IEEE 754 bit-patterns and masks.
 */
#define TRIO_DOUBLE_INDEX(x) (((unsigned char *)&amp;internalEndianMagic)[7-(x)])
static TRIO_CONST double internalEndianMagic = 7.949928895127363e-275;
#endif</pre><pre style="word-wrap: break-word; "><span class="Apple-style-span" style="font-family: arial; font-size: 13px; white-space: normal;">pretty weird stuff.</span></pre><div><span class="Apple-style-span" style="font-family: arial; font-size: 13px;">
<br class="webkit-block-placeholder"></span></div></span></div>

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