gamma_r(3M)

NAME | SYNOPSIS | DESCRIPTION | IDIOSYNCRASIES | RETURN VALUES | ATTRIBUTES | SEE ALSO | NOTES

NAME

lgamma, lgamma_r, gamma, gamma_r- log gamma function

SYNOPSIS

cc [ flag ... ] file ... -lm [ library ... ]
#include <math.h>
extern int signgam;

double lgamma(double x);
double lgamma_r(double x, int *signgamp);

DESCRIPTION

Both lgamma() and lgamma_r() return



where



for x > 0 and



for x < 1.

lgamma() uses the external integer signgam to return the sign of |~(x) while lgamma_r() uses the user-allocated space addressed by signgamp.

IDIOSYNCRASIES

In the case of lgamma(), do not use the expression signgam*exp(lgamma(x)) to compute



Instead compute lgamma() first:

---

lg = lgamma(x); g = signgam*exp(lg);

---

only after lgamma() has returned can signgam be correct. Note that |~(x) must overflow when x is large enough, underflow when -x is large enough, and generate a division by 0 exception at the singularities x a nonpositive integer.

RETURN VALUES

For exceptional cases, matherr(3M) tabulates the values to be returned as dictated by various Standards.

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
MT-Level	See NOTES below.

SEE ALSO

matherr(3M), attributes(5)

NOTES

Although lgamma_r() is not mentioned by POSIX.4a Draft 6, it was added to complete the functionality provided by similar thread-safe functions. This interface is subject to change to be compatible with the "spirit" of POSIX.4a when it is approved as a standard.

When compiling multi-thread applications, the _REENTRANT flag must be defined on the compile line. This flag should only be used in multi-thread applications.

lgamma() is unsafe in multithreaded applications. lgamma_r() should be used instead.

SunOS 5.8  Last Revised 29 Dec 1996

NAME | SYNOPSIS | DESCRIPTION | IDIOSYNCRASIES | RETURN VALUES | ATTRIBUTES | SEE ALSO | NOTES