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

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.

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.