[geos-devel] Re: Strange problem with ISNAN macro

[=?GB2312?B?zfXTwL3c?=]

Hello Ciao:

I try to test the return value of ISNAN(DoubleNotANumber), it's true
that always failure.
The macro ISNAN is defined with function _isnan what returns a nonzero
value if the argument x is a NAN,

There are two methods to generate NAN.
1. this method is come from MSDN.
       unsigned long nan[2]={0xffffffff, 0x7fffffff};
       double g = *( double* )nan;
  g is NAN, and ISNAN(g) will return true.
2. the other method is come from stl
       double g = numeric_limits<double>::quiet_NaN();
 g is NAN too, and ISNAN(g) will return true.

it's seems that DoubleNotANumber define with 1.7e-308 is not NAN.

does this can solve your problem.

Best regards to everyone.

>  ------------------------------
>
>  Message: 2
>  Date: Wed, 7 May 2008 11:58:44 +0200
>  From: "Simone Giannecchini" <simone.giannecchini at geo-solutions.it>
>  Subject: [geos-devel] Strange problem with ISNAN macro
>  To: geos-devel at lists.osgeo.org
>  Message-ID:
>         <961f4d9e0805070258i557340a7qef736bcc1176d189 at mail.gmail.com>
>  Content-Type: text/plain; charset=ISO-8859-1
>
>  Hi list,
>  I am resurrecting some old code (1.5 years almost) which depended on a
>  previous version of GEOS and I am having a strange problem.
>  My code was used on windows platforms without (apparent :-) )
>  problems. I have some wrapper classes of Coordinate where I make use
>  of the ISNAN(x)  macro defined in platform.h.
>  I have built my app against GEOS 3.0  on an intel win xp pro using vs
>  7.1 but now strange enough, in my code this test
>  ISNAN(DoubleNotANumber) always fails, causing me quite a lot of
>  headaches.
>  I have not investigated this problem too much yet, hence the solutions
>  might be simple and immediate, if so, I apologize in advance! :-)
>
>  Does anyone have an idea about how to tackle this problem?
>
>
>  Ciao,
>  Simone.
>
>  --
>  -------------------------------------------------------
>  Eng. Simone Giannecchini
>  President /CEO GeoSolutions S.A.S.
>  Via Carignoni 51
>  55041 Camaiore (LU)
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