## Linux and UNIX Man Pages

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# gammaf_r(3m) [opensolaris man page]

```lgamma(3M)						  Mathematical Library Functions						lgamma(3M)

NAME
lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, gamma, gammaf, gammal, gamma_r, gammaf_r, gammal_r - log gamma function

SYNOPSIS
c99 [ flag... ] file... -lm [ library... ]
#include <math.h>

extern int signgam;

double lgamma(double x);

float lgammaf(float x);

long double lgammal(long double x);

double gamma(double x);

float gammaf(float x);

long double gammal(long double x);

double lgamma_r(double x, int *signgamp);

float lgammaf_r(float x, int *signgamp);

long double lgammal_r(long double x, int *signgamp);

double gamma_r(double x, int *signgamp);

float gammaf_r(float x, int *signgamp);

long double gammal_r(long double x, int *signgamp);

DESCRIPTION
These functions return

ln||~(x)|

where

|~(x) = integral from 0 to +Infinity of pow(t,x-1)*exp(-t) dt

for x > 0 and

|~(x) = n/(|~(1-x)sin(nx))

for x < 1.

These  functions  use  the external integer signgam to return the sign of |~(x) while lgamma_r() and gamma_r() use the user-allocated space

RETURN VALUES
Upon successful completion, these functions return the logarithmic gamma of x.

If x is a non-positive integer, a pole error occurs and these functions return +HUGE_VAL, +HUGE_VALF, and +HUGE_VALL, respectively.

If x is NaN, a NaN is returned.

If x is 1 or 2, +0 shall be returned.

If x is +-Inf, +Inf is returned.

ERRORS
These functions will fail if:

Pole Error    The x argument is a negative integer or 0.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero  floating-point  exception
is raised.

USAGE
An  application	wanting  to  check  for  exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if
fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception  has  been  raised.  An  application  should
either examine the return value or check the floating point exception flags to detect exceptions.

In the case of lgamma(), do not use the expression signgam*exp(lgamma(x)) to compute

`g  := |~(x)'

lg = lgamma(x); g = signgam*exp(lg);

only  after  lgamma() has returned can signgam be correct. Note that |~(x) must overflow when x is large enough, underflow when -x is large
enough, and generate a division by 0 exception at the singularities x a nonpositive integer.

ATTRIBUTES
See attributes(5) for descriptions of the following attributes:

+-----------------------------+-----------------------------+
|      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
+-----------------------------+-----------------------------+
|Interface Stability	     |See below.		   |
+-----------------------------+-----------------------------+
|MT-Level		     |See below.		   |
+-----------------------------+-----------------------------+

The lgamma(), lgammaf(), lgammal(), and gamma() functions are Standard. The lgamma_r(), lgammaf_r(),  lgammal_r(),  gamma_r(),  gammaf_r(),
and gammal_r(), functions are Stable.

The  lgamma(),  lgammaf(),  lgammal(),  gamma(), gammaf(), and gammal() functions are Unsafe in multithreaded applications. The lgamma_r(),
lgammaf_r(), lgammal_r(), gamma_r(), gammaf_r(), and gammal_r() functions are MT-Safe and should be used instead.