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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, signgam -- 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
       The functionality described on this reference page is aligned with  the
       ISO C  standard.  Any  conflict between the requirements described here
       and the ISO C standard is unintentional. This  volume  of  POSIX.1-2008
       defers to the ISO C standard.
                                               _            _
       These  functions  shall compute log_e || (x)| where | (x) is defined as
       Io_^ -tt^ x-1dt.  The argument x need not  be  a  non-positive  integer
       (| (x) is defined over the reals, except the non-positive integers).
       If  x  is  NaN,  -Inf,  or  a negative integer, the value of signgam is
       unspecified.
       These functions need not 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 POSIX.1-2008, Section 4.19, 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, 2013 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal  and  Electronics  Engineers,  Inc  and  The  Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum  1  applied.)  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.unix.org/online.html .
       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,  see  https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                           LGAMMA(3P)