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Date: Wed, 06 Mar 2013 23:06:04 +0200
From: Eli Zaretskii <eliz AT gnu DOT org>
Subject: Re: Printing sign of NaN.
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To: Juan Manuel Guerrero <juan DOT guerrero AT gmx DOT de>
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> Date: Wed, 06 Mar 2013 20:16:42 +0100
> From: Juan Manuel Guerrero <juan DOT guerrero AT gmx DOT de>
> CC: Eli Zaretskii <eliz AT gnu DOT org>
> 
>  > Isn't NaN always negative?  Do you succeed in printing both negative
>  > and positive NaN with this patch?
> 
> Yes, I can print both signs with this change.

And what about reading a signed NaN?  Does it produce a value of that
same sign when printed afterwards?

> In this line:
> 
>        if (_ldouble < 0 || (IS_NAN(ieee_value) && ieee_value.ldt.sign))
> 
> _ldouble < 0 is always false if _ldouble is a NaN.  I was not aware of this.

A NaN causes any test to fail, so _ldouble < 0 will be false and I
would also expect _ldouble > 0 to be false.  In fact, one way of
detecting a NaN is to compare it with itself and see if the result
comes out as not equal.  (You need to trick the compiler into not
being too smart, to see that, though.)