FP_NAN
#define fpclassify(x) __builtin_fpclassify(FP_NAN, FP_INFINITE, FP_NORMAL, \
isnan(__x_c) ? FP_NAN : \
#define classify(X) __builtin_fpclassify(FP_NAN,FP_INF,FP_NOR,FP_SUB,FP_ZERO,X)
if (classify(__builtin_nan("0")) != FP_NAN)