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

     1  #include "libm.h"
     2  
     3  // FIXME: macro in math.h
     4  int __signbit(double x)
     5  {
     6  	union {
     7  		double d;
     8  		uint64_t i;
     9  	} y = { x };
    10  	return y.i>>63;
    11  }
    12  
    13