# FreeBSD Manual Pages

```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,	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|| (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), tgammaf(x),	and tgammal(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
D_	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	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
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.

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 | (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			       December	8, 2017				   BSD
```

NAME | LIBRARY | SYNOPSIS | 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+12.0-RELEASE>