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
     external 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
     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.

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
     precision 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 13.1-RELEASE-p6        December 8, 2017        FreeBSD 13.1-RELEASE-p6