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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 differ (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  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  logarith-
       mic 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 Condi-
       tions 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 .

IEEE/The Open Group                  2003                           LGAMMA(3P)