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

     1  #include <math.h>
     2  
     3  float logbf(float x)
     4  {
     5  	if (!isfinite(x))
     6  		return x * x;
     7  	if (x == 0)
     8  		return -1/(x*x);
     9  	return ilogbf(x);
    10  }