This manual page is part of the POSIX Programmer’s Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

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lgamma, lgammaf, lgammal - log gamma function

#include <math.h>

double lgamma(doublex);

float lgammaf(floatx);

long double lgammal(long doublex);

extern int signgam;

These functions shall compute

The argument

xneed 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

errnoto zero and callfeclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, iferrnois non-zero orfetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Upon successful completion, these functions shall return the logarithmic gamma of

x.If

xis a non-positive integer, a pole error shall occur andlgamma(),lgammaf(), andlgammal() 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(), andlgammal() shall return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (having the same sign as the correct value), respectively.If

xis NaN, a NaN shall be returned.If

xis 1 or 2, +0 shall be returned.If

xis ±Inf, +Inf shall be returned.

These functions shall fail if:

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then

Pole Error The xargument is a negative integer or zero.If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errnoshall 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. errnoshall 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.

None.

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.

None.

None.

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>

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 .

IEEE/The Open Group |
LGAMMA (P) | 2003 |