LGAMMA(3) Linux Programmer's Manual LGAMMA(3)NAME
lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r - log gamma
function
SYNOPSIS
#include <math.h>
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);
Compile with -std=c99; link with -lm.
DESCRIPTION
For the definition of the Gamma function, see tgamma(3).
The lgamma() function returns 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() etc. have been introduced; they return this sign via
the parameter signp.
For non-positive integer values of x, lgamma() returns HUGE_VAL, sets
errno to ERANGE and raises the zero divide exception. (Similarly,
lgammaf() returns HUGE_VALF and lgammal() returns HUGE_VALL.)
ERRORS
In order to check for errors, set errno to zero and call feclearex‐
cept(FE_ALL_EXCEPT) before calling these functions. On return, if errno
is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW |
FE_UNDERFLOW) is non-zero, an error has occurred.
A range error occurs if x is too large. A pole error occurs if x is a
negative integer or zero.
CONFORMING TO
C99, SVr4, 4.3BSD
SEE ALSOtgamma(3)
2002-08-10 LGAMMA(3)
