log2, log2f, log2l - base 2 logarithm function

Syntax	#include <math.h> C11 double log2(double x); float log2f(float x); long double log2l(long double x); (End)
Description	These functions compute the logarithm of the positive floating-point number x to the base 2.
Return val.	log2(x)	for a positive x.
	-HUGE_VAL -HUGE_VALF -HUGE_VALL	depending on the function type, if x is less than or equal to 0. errno is set to indicate the error.
Errors	log2(), log2f() and log2l() will fail if:
	EDOM	The value of x is negative.
	ERANGE	The value of x is 0.
See also	exp(), exp2(), log(), log10(), pow(), sqrt(), math.h.