lgamma, lgammaf, lgammal, gamma, signgam - compute logarithm of gamma function

Syntax	#include <math.h> double gamma(double x); double lgamma(double x); C11 float lgammaf(float x); long double lgammal(long double x); (End) extern int signgam;
Description	These functions compute the natural logarithm of the absolute value of the mathematical gamma function for a given floating-point number x: The sign of this value is stored as +1 or -1 in the internal C variable signgam. The signgam variable must not be defined by the user.
Return val.	log(|tgamma(x)|)	if successful.
	HUGE_VAL HUGE_VALF HUGE_VALL	depending on the function type, if the correct value results in an overflow. errno is set to indicate the error.
	HUGE_VAL HUGE_VALF HUGE_VALL	depending on the function type, if x is a non-positive integer. errno is set to indicate the error.
Errors	gamma(), lgamma(), lgammaf() and lgammal() will fail if:
	ERANGE	Overflow; the return value is too large.
	EDOM	x is a non-positive integer.
See also	fabs(), tgamma(), math.h.