# lgamma(3) - NetBSD Manual Pages

Command: Section: Arch: Collection:
```LGAMMA(3)               NetBSD Library Functions Manual              LGAMMA(3)

NAME
lgamma, lgammaf, lgamma_r, lgammaf_r, gamma, gammaf, gamma_r, gammaf_r,
tgamma, tgammaf -- log gamma function

LIBRARY
Math Library (libm, -lm)

SYNOPSIS
#include <math.h>

extern int signgam;

double
lgamma(double x);

float
lgammaf(float x);

double
lgamma_r(double x, int *sign);

float
lgammaf_r(float x, int *sign);

double
gamma(double x);

float
gammaf(float x);

double
gamma_r(double x, int *sign);

float
gammaf_r(float x, int *sign);

double
tgamma(double x);

float
tgammaf(float x);

DESCRIPTION
lgamma(x) returns ln||¯(x)|.

The external integer signgam returns the sign of |¯(x).

lgamma_r() is a reentrant interface that performs identically to
lgamma(), differing in that the sign of |¯(x) is stored in the location
pointed to by the sign argument and signgam is not modified.

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() has returned can signgam be correct.

RETURN VALUES
lgamma() returns appropriate values unless an argument is out of range.
Overflow will occur for sufficiently large positive values, and non-posi-
tive integers.  For large non-integer negative values, tgamma() will
underflow.  On the VAX, the reserved operator is returned, and errno is
set to ERANGE.