[libvirt] [PATCH 2/2] util: Cast to 'long double' when calling isnan()

[Martin Kletzander]

On Mon, Jan 02, 2017 at 07:15:31PM +0100, Andrea Bolognani wrote:
>Clang 3.9 chokes when calling isnan() on a double variable:
>
>  util/virxml.c:153:21: error: implicit conversion increases
>                        floating-point precision: 'double' to
>                        'long double' [-Werror,-Wdouble-promotion]
>          (isnan(obj->floatval))) {
>           ~~~~~~~~~~~^~~~~~~~~
>  /usr/include/math.h:360:46: note: expanded from macro 'isnan'
>  #  define isnan(x) __MATH_TG ((x), __isnan, (x))
>                     ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
>  /usr/include/math.h:295:16: note: expanded from macro '__MATH_TG'
>     : FUNC ## l ARGS)
>       ~~~~~~~~~ ^~~~
>
>Note how the wrong version of isnan() is being called: isnanl()
>is for 'long double's, but obj->floatval is a double and a
>suitable version should be called instead.
>

I don't know where do you see that ^^.  Good eyes, I guess =)

>Cast the value to 'long double' to make the compiler happy.
>---
>Clang seems to be tripping on the specific way the isnan()
>macro is defined in recent glibc versions; more specifically,
>if I replace the current definition in <math.h> with the one
>that predates the introduction of the __MATH_TG() macro, I
>can get the current code to compile. I was not able to find
>anything wrong with the __MATH_TG() macro though.
>

This sounds like a glibc <=> clang problem that we shoudn't introduce
more complexity for.  Also *I* don't see this error, for a change =)


Martin
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