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Date: Fri, 28 May 2004 10:54:37 -0500
From: Brian Ford <ford AT vss DOT fsi DOT com>
Reply-To: cygwin AT cygwin DOT com
To: mathias DOT wagner AT philips DOT com
cc: cygwin AT cygwin DOT com
Subject: Re: GCC 3.3.1 problem with printf %Lg %Lg and -m128bit-long-double compile option
In-Reply-To: <OF4B525423.BF84D3AE-ONC1256EA2.00331803-C1256EA2.003360F4@philips.com>
Message-ID: <Pine.CYG.4.58.0405281045070.1584@fordpc.vss.fsi.com>
References: <OF4B525423 DOT BF84D3AE-ONC1256EA2 DOT 00331803-C1256EA2 DOT 003360F4 AT philips DOT com>
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On Fri, 28 May 2004, mathias.wagner wrote:

>          To:     "Gerrit @ cygwin" <cygwin at cygwin dot com>

http://www.cygwin.com/acronyms/#PCYMTNQREAIYR

> Meanwhile I have had some help from another colleague here at Philips and
> he found out that the -m96bit-long-double compile option works fine.

My understanding is that this is the default ie. no switch requried.

> Note that 96 bit is what a long double takes. This makes sense in
> conjunction with what Brian said: The alignment of the parameters handed
> over to a function is changed when using -m128bit-long-double, and hence
> all functions affected must be recompiled - so presumably cygwin itself.

Yes.

> There was no particular reason for using -m128bit-long-double other than
> that I have always used it, and I will switch to -m96bit-long-double.

It might have performed better with respect to caching, but YMMV.

> But perhaps one could insert somewhere in gcc a warning when using such
> a combination of compile options. I know it is in the documentation
> somewhere, but compiler warnings are much more visible... :-)

You could take this up on the gcc list if it is still important to you,
but I suspect they would frown on the idea.  The philosophy goes
something like this:

You had to read the documentation to discover that this switch existed.
It is not a compiler warnings job to advise you to read the documentation
more carefully.  It would also penalize those that did read the docs, so
they would want a way to turn off the gratuitous warning with via another
switch or attribute.

Can you see why this isn't a good idea?

-- 
Brian Ford
Senior Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
the best safety device in any aircraft is a well-trained pilot...

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