# FreeBSD Manual Pages

```LGAMMA(3)	       FreeBSD Library Functions Manual		     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
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);

long double
tgammal(long double x);

DESCRIPTION
lgamma(x),	lgammaf(x), and	lgammal(x) return ln|<Gamma>(x)|.  The exter-
nal integer signgam returns the sign of <Gamma>(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 <Gamma>(x).

The tgamma(x), tgammaf(x),	and tgammal(x) functions return	<Gamma>(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 :=
<Gamma>(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	argu-
ments it is accurate to within one	unit in	the last place.	 Exponentia-
tion 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 ap-
propriate 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.

BUGS
To	conform	with newer C/C++ standards, a stub implementation for tgammal
was committed to the math library,	where tgammal is mapped	to tgamma.
Thus, the numerical accuracy is at	most that of the 53-bit	double preci-
sion implementation.

SEE ALSO
math(3)

STANDARDS
The lgamma(), lgammaf(), lgammal(), tgamma(), tgammaf(), and tgammal()
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 <Gamma>(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.

FreeBSD	13.0		       December	8, 2017			  FreeBSD 13.0
```

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | IDIOSYNCRASIES | RETURN VALUES | BUGS | SEE ALSO | STANDARDS | HISTORY

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=lgamma&sektion=3&manpath=FreeBSD+13.0-RELEASE>