HelenOS sources

FP_NAN             97 uspace/lib/c/include/math.h #define fpclassify(x)  __builtin_fpclassify(FP_NAN, FP_INFINITE, FP_NORMAL, FP_SUBNORMAL, FP_ZERO, (x))
FP_NAN            122 uspace/lib/c/include/math.h #define isnan(x)       (fpclassify(x) == FP_NAN)
FP_NAN             97 uspace/lib/posix/include/libc/math.h #define fpclassify(x)  __builtin_fpclassify(FP_NAN, FP_INFINITE, FP_NORMAL, FP_SUBNORMAL, FP_ZERO, (x))
FP_NAN            122 uspace/lib/posix/include/libc/math.h #define isnan(x)       (fpclassify(x) == FP_NAN)