LGAMMA(3)

NAME
lgamma, lgamma_r, lgammaf, lgammaf_r, lgammal, lgammal_r, gamma, gamma_r, gammaf, gammaf_r, tgamma, tgammaf, tgammal, - log gamma functions, gamma function

LIBRARY
libm

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);
long double
tgammal(long double x);

DESCRIPTION
lgamma(x), lgammaf(x), and lgammal(x) return ln|Γ(x)|. The external integer signgam returns the sign of Γ(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 Γ(x).

The tgamma(x), tgammaf(x), and tgammal(x) functions return Γ(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 := Γ(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. Exponentiation 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(), tgammaf(), and tgammal() functions are expected to conform to isoC-99.

HISTORY
The lgamma() function appeared in 4.3BSD. The gamma() function appeared in 4.4BSD as a function which computed Γ(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. The 128-bit long double version of tgammal() replaced the 80-bit stub version in version in FreeBSD 14.1, thanks to an appropriate implementation from Arm.