NAME
lgamma, lgammaf, lgammal - log gamma function
SYNOPSIS
#include <math.h>
double lgamma(double x);
float lgammaf(float x);
long double lgammal(long double x);
extern int signgam;
DESCRIPTION
These functions shall compute
The argument x need not be a non-positive integer (Gamma(x) is defined
over the reals, except the non-positive integers).
The sign of Gamma(x) is returned in the external integer signgam.
These functions need not be reentrant. A function that is not required
to be reentrant is not required to be thread-safe.
An application wishing to check for error situations should set errno
to zero and call feclearexcept(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.
RETURN VALUE
Upon successful completion, these functions shall return the
logarithmic gamma of x.
If x is a non-positive integer, a pole error shall occur and lgamma(),
lgammaf(), and lgammal() shall return +HUGE_VAL, +HUGE_VALF, and
+HUGE_VALL, respectively.
If the correct value would cause overflow, a range error shall occur
and lgamma(), lgammaf(), and lgammal() shall return ±HUGE_VAL,
±HUGE_VALF, and ±HUGE_VALL (having the same sign as the correct value),
respectively.
If x is NaN, a NaN shall be returned.
If x is 1 or 2, +0 shall be returned.
If x is ±Inf, +Inf shall be returned.
ERRORS
These functions shall fail if:
Pole Error
The x argument is a negative integer or zero.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-
zero floating-point exception shall be raised.
Range Error
The result overflows.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow
floating-point exception shall be raised.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
On error, the expressions (math_errhandling & MATH_ERRNO) and
(math_errhandling & MATH_ERREXCEPT) are independent of each other, but
at least one of them must be non-zero.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
exp() , feclearexcept() , fetestexcept() , isnan() , the Base
Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of
Error Conditions for Mathematical Functions, <math.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .