log2, log2f, log2l - base 2 logarithm function

Definition	#include <math.h> double log2(double x); float log2f(double x); (C11) long double log2l(long double x); (C11) These functions calculate the natural logarithm of the positive floating-point number x to the base 10.
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. In addition, errno is set to EDOM (domain error) or if x is equal to 0. In addition, errno is set to ERANGE.
See also	log, log10, exp, exp2