log, logf, logl - natural logarithm function

Syntax	#include <math.h> double log(double x); C11 float logf(float x); long double logl(long double x); (End)
Description	These functions compute the natural logarithm of the positive floating-point number x to the base e.
Return val.	ln(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	log(), logf() and logl() will fail if:
	EDOM	The value of x is negative.
	ERANGE	The value of x is 0.
See also	exp(), exp2(), log2(), log10(), pow(), sqrt(), math.h.