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Re: Old patches from Red Hat

From: Daniel J Sebald
Subject: Re: Old patches from Red Hat
Date: Thu, 28 Apr 2005 17:37:14 -0500
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.3) Gecko/20041020

John W. Eaton wrote:
On 28-Apr-2005, Daniel J Sebald wrote:

| Can some of these definitions and routines be replaced with
| something from the header file "ieee754.h"?  In there are a variety
| of helper routines and structures for accessing the sign bit.

Is that header file defined by any standard?

Good question. I've searched the web. My guess is that it might be part of the GNU C library definition (not actually in the library though because it is just definitions). As for machines that don't use IEEE-754 floating point, I don't know how those are handled.

On my system, /usr/include/ieee754.h does not include any declarations
for functions or any macros that appear to be related to accessing the
sign bit.  All I see are some declarations of some structures for
defining the format of IEEE floating point values.  But maybe I'm
missing something.

That does appear to be it. Perhaps the designers felt a bit field pointer was simple enough. So, lo_ieee_signbit(x) could be defined as casting the address of x to the ieee754_float type and using (pointer)->negative. I.e.,

#define lo_ieee_signbit(x) (((ieee754_float *)&x).ieee->negative)

That gets rid of all the

#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1

contortions.  However, the issue of portability to non-GNU compilers is still 


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