double lgamma(double x);
float lgammaf(float x);
long double lgammal(long double x);
double lgamma_r(double x, int *signp);
float lgammaf_r(float x, int *signp);
long double lgammal_r(long double x, int *signp);
extern int signgam;
Link with -lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
lgamma_r(), lgammaf_r(), lgammal_r():
_BSD_SOURCE || _SVID_SOURCE
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
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 func-
tions lgamma_r(), lgammaf_r(), and lgammal_r() have been introduced;
they return the sign via the argument signp.
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
If x is a nonpositive integer, a pole error occurs, and the functions
Pole error: x is a nonpositive integer
errno is set to ERANGE (but see BUGS). A divide-by-zero float-
ing-point exception (FE_DIVBYZERO) is raised.
Range error: result overflow
errno is set to ERANGE. An overflow floating-point exception
(FE_OVERFLOW) is raised.
The lgamma() functions are specified in C99, POSIX.1-2001, and
POSIX.1-2008. signgam is specified in POSIX.1-2001 and POSIX.1-2008,
but not in C99. The lgamma_r() functions are nonstandard, but present
on several other systems.
In glibc 2.9 and earlier, when a pole error occurs, errno is set to
EDOM; instead of the POSIX-mandated ERANGE. Since version 2.10, glibc
does the right thing.
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