FreeBSD 11.0(freebsd section 3)man page for lgammal

LGAMMA(3)						   BSD Library Functions Manual 						 LGAMMA(3)

NAME
lgamma, lgamma_r, lgammaf, lgammaf_r, lgammal, lgammal_r, gamma, gamma_r, gammaf, gammaf_r, tgamma, tgammaf -- log gamma functions, gamma function LIBRARY
Math Library (libm, -lm) SYNOPSIS
#include <math.h> extern int signgam; double lgamma(double x); double lgamma_r(double x, int *signgamp); float lgammaf(float x); float lgammaf_r(float x, int *signgamp); long double lgammal(long double x); long double lgammal_r(long double x, int *signgamp); double gamma(double x); double gamma_r(double x, int *signgamp); float gammaf(float x); float gammaf_r(float x, int *signgamp); long double tgamma(double x); float tgammaf(float x); DESCRIPTION
_ _ lgamma(x), lgammaf(x), and lgammal(x) return ln|| (x)|. The external integer signgam returns the sign of | (x). lgamma_r(x, signgamp), lgammaf_r(x, signgamp), and lgammal_r(x, signgamp)_provide the same functionality as lgamma(x), lgammaf(x), and lgammal(x), but the caller must provide an integer to store the sign of | (x). _ The tgamma(x) and tgammaf(x) functions return | (x), with no effect on signgam. gamma(), gammaf(), gamma_r(), and gammaf_r() are deprecated aliases for lgamma(), lgammaf(), lgamma_r(), and lgammaf_r(), respectively. IDIOSYNCRASIES
_ Do not use the expression ``signgam*exp(lgamma(x))'' to compute g := | (x). Instead use a program like this (in C): lg = lgamma(x); g = signgam*exp(lg); Only after lgamma() or lgammaf() has returned can signgam be correct. For arguments in its range, tgamma() is preferred, as for positive arguments it is accurate to within one unit in the last place. Exponenti- ation of lgamma() will lose up to 10 significant bits. RETURN VALUES
gamma(), gammaf(), gammal(), gamma_r(), gammaf_r(), gammal_r(), lgamma(), lgammaf(), lgammal(), lgamma_r(), lgammaf_r(), and lgammal_r() return appropriate values unless an argument is out of range. Overflow will occur for sufficiently large positive values, and non-positive integers. For large non-integer negative values, tgamma() will underflow. SEE ALSO
math(3) STANDARDS
The lgamma(), lgammaf(), lgammal(), tgamma(), and tgammaf() functions are expected to conform to ISO/IEC 9899:1999 (``ISO C99''). HISTORY
_ The lgamma() function appeared in 4.3BSD. The gamma() function appeared in 4.4BSD as a function which computed | (x). This version was used in FreeBSD 1.1. The name gamma() was originally dedicated to the lgamma() function, and that usage was restored by switching to Sun's fdlibm in FreeBSD 1.1.5. The tgamma() function appeared in FreeBSD 5.0. BSD
September 12, 2014 BSD