lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam - log gamma function

       In glibc 2.9 and earlier, when a pole error occurs, errno is set to EDOM; instead of  the  POSIX-mandated
       ERANGE.  Since glibc 2.10, glibc does the right thing.

       For the definition of the Gamma function, see tgamma(3).

       The  lgamma(),  lgammaf(),  and lgammal() functions return the natural logarithm of the absolute value of
       the Gamma function.  The sign of the Gamma function is returned in the external integer signgam  declared
       in <math.h>.  It is 1 when the Gamma function is positive or zero, -1 when it is negative.

       Since  using  a  constant location signgam is not thread-safe, the functions lgamma_r(), lgammaf_r(), and
       lgammal_r() have been introduced; they return the sign via the argument signp.

       See math_error(7) for information on how to determine whether an error has occurred  when  calling  these
       functions.

       The following errors can occur:

       Pole error: x is a nonpositive integer
              errno  is  set to ERANGE (but see BUGS).  A divide-by-zero floating-point exception (FE_DIVBYZERO)
              is raised.

       Range error: result overflow
              errno is set to ERANGE.  An overflow floating-point exception (FE_OVERFLOW) is raised.

lgamma()
       lgammaf()
       lgammal()
              C99, POSIX.1-2001.

       signgam
              POSIX.1-2001.

       lgamma_r()
       lgammaf_r()
       lgammal_r()
              None.

       Math library (libm, -lm)

       lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam - log gamma function

       On success, these functions return the natural logarithm of Gamma(x).

       If x is a NaN, a NaN is returned.

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

       If x is positive infinity or negative infinity, positive infinity is returned.

       If x is a nonpositive integer, a pole error occurs, and the functions return  +HUGE_VAL,  +HUGE_VALF,  or
       +HUGE_VALL, respectively.

       If  the  result  overflows,  a  range  error  occurs,  and  the  functions return HUGE_VAL, HUGE_VALF, or
       HUGE_VALL, respectively, with the correct mathematical sign.

tgamma(3)

Linux man-pages 6.9.1                              2024-05-02                                          lgamma(3)

lgamma()
       lgammaf()
       lgammal()
              C11, POSIX.1-2008.

       signgam
              POSIX.1-2008.

       lgamma_r()
       lgammaf_r()
       lgammal_r()
              None.

#include<math.h>doublelgamma(doublex);floatlgammaf(floatx);longdoublelgammal(longdoublex);doublelgamma_r(doublex,int*signp);floatlgammaf_r(floatx,int*signp);longdoublelgammal_r(longdoublex,int*signp);externintsigngam;

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       lgamma():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       lgammaf(), lgammal():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       lgamma_r(), lgammaf_r(), lgammal_r():
           /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       signgam:
           _XOPEN_SOURCE
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE