This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       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.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 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 .

       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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                        TGAMMA(3POSIX)

       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.1‐2017 defers to the ISO C standard.

--

       These functions shall fail if:

       Domain Error
                   The value of x is a negative integer, or x is -Inf.

                   If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then  errno  shall  be
                   set  to  [EDOM].   If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
                   then the invalid floating-point exception shall be raised.

       Pole Error  The value of x is 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 value 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.

       These functions may fail if:

       Domain Error
                   The value of x is a negative integer.

                   If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then  errno  shall  be
                   set  to  [EDOM].   If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
                   then the invalid floating-point exception shall be raised.

       Pole Error  The value of x is 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 underflows.

                   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 underflow floating-point exception shall be raised.

       Thefollowingsectionsareinformative.

       None.

       It is possible that the error response for a negative integer argument may be changed to a pole error and
       a return value of ±Inf.

       tgamma, tgammaf, tgammal — compute gamma() function

       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.

       This  function  is  named  tgamma()  in order to avoid conflicts with the historical gamma() and lgamma()
       functions.

       Upon successful completion, these functions shall return the gamma of x.

       If  x  is  a  negative  integer,  a  domain  error  may  occur  and  either  a  NaN  (if supported) or an
       implementation-defined value shall be returned.  On systems that support  the  IEC  60559  Floating-Point
       option, a domain error shall occur and a NaN shall be returned.

       If  x  is  ±0,  tgamma(),  tgammaf(),  and  tgammal() shall return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL,
       respectively.  On systems that support the IEC 60559 Floating-Point option, a  pole  error  shall  occur;
       otherwise, a pole error may occur.

       If  the  correct  value  would  cause  overflow,  a  range error shall occur and tgamma(), tgammaf(), and
       tgammal() shall return ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL, respectively, with  the  same  sign  as  the
       correct value of the function.

       If  the  correct  value  would  cause  underflow,  and is not representable, a range error may occur, and
       tgamma(), tgammaf(), and tgammal() shall return 0.0, or (if IEC 60559 Floating-Point is not supported) an
       implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

       If the correct value would cause underflow, and is representable, a range error may occur and the correct
       value shall be returned.

       If x is subnormal and 1/x is representable, 1/x should be returned.

       If x is NaN, a NaN shall be returned.

       If x is +Inf, x shall be returned.

       If x is -Inf, a domain error shall occur, and a NaN shall be returned.

feclearexcept(), fetestexcept(), lgamma()

       The Base Definitions volume of POSIX.1‐2017, Section4.20, TreatmentofErrorConditionsforMathematicalFunctions, <math.h>

       #include <math.h>

       double tgamma(double x);
       float tgammaf(float x);
       long double tgammal(long double x);