logb, logbf, logbl - get exponent part of floating-point number

Syntax	#include <math.h> double logb(double x); C11 float logbf(float x); long double logbl(long double x); (End)
Description	These functions are identical to the corresponding ilogb()-functions except that they do not return the exponent part of x as int, but as a signed floating-point number.
Return val.	Exponent part of x
		if successful
	-HUGE_VAL -HUGE_VALF -HUGE_VALL	depending on the function type, if x = 0.0. errno is set to indicate the error.
Errors	logb(), logbf() and logbl() will fail if:
	EDOM	The value of x is 0.0.
See also	ilogb(), math.h.