FP_ILOGBNAN
else if (hx>0x7fff000000000000LL || lx!=0) return FP_ILOGBNAN;
else if ((hx&0x7fffffff|lx)!=0) return FP_ILOGBNAN;
else if (hx>0x7ff00000 || lx!=0) return FP_ILOGBNAN;
else if (hx>0x7f800000) return FP_ILOGBNAN;
ATF_CHECK_EQ(FP_ILOGBNAN, ilogb(NAN));
ATF_CHECK_EQ(FP_ILOGBNAN, ilogbf(NAN));
ATF_CHECK_EQ(FP_ILOGBNAN, ilogbl(NAN));