From: "David Leimbach" <leimy2k@gmail.com>
To: 9fans@cse.psu.edu
Subject: [9fans] fun and scary evil C code
Date: Wed, 19 Dec 2007 07:15:09 -0800 [thread overview]
Message-ID: <3e1162e60712190715q3f50d601sd88b1e0c6c74afc8@mail.gmail.com> (raw)
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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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next reply other threads:[~2007-12-19 15:15 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-19 15:15 David Leimbach [this message]
2007-12-19 20:37 ` Russ Cox
2007-12-19 22:32 ` Robert William Fuller
2007-12-19 22:38 ` erik quanstrom
2007-12-19 22:51 ` Bakul Shah
2007-12-20 0:18 ` dave.l
2007-12-20 0:33 ` dave.l
2007-12-20 0:51 ` erik quanstrom
2007-12-20 9:29 ` roger peppe
2007-12-20 13:02 ` erik quanstrom
2007-12-20 16:29 Russ Cox
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