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1extern int __isnanf(float f);2extern int __isnan(double f);3extern int __isnanl(long double f);4#define isnan(x) \5 (sizeof (x) == sizeof (float) \6 ? __isnanf (x) \7 : sizeof (x) == sizeof (double) \8 ? __isnan (x) : __isnanl (x))9 10