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LGAMMA(3P)                 POSIX Programmer's Manual                LGAMMA(3P)



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

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 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.

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 excep-
       tion 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 indepen-
       dent 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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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                  2003                           LGAMMA(3P)