github.com/afumu/libc@v0.0.6/musl/src/math/__fpclassify.c (about)

     1  #include <math.h>
     2  #include <stdint.h>
     3  
     4  int __fpclassify(double x)
     5  {
     6  	union {double f; uint64_t i;} u = {x};
     7  	int e = u.i>>52 & 0x7ff;
     8  	if (!e) return u.i<<1 ? FP_SUBNORMAL : FP_ZERO;
     9  	if (e==0x7ff) return u.i<<12 ? FP_NAN : FP_INFINITE;
    10  	return FP_NORMAL;
    11  }