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



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

NAME
       tgamma, tgammaf, tgammal - compute gamma() function

SYNOPSIS
       #include <math.h>

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


DESCRIPTION
       These functions shall compute the gamma() function of x.

       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 Gamma( x).

       If  x  is  a  negative integer, a domain error shall occur, and either a NaN (if supported), or an implementation-defined
       value shall be returned.

       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 x is NaN, a NaN shall be returned.

       If x is +Inf, x shall be returned.

       If  x  is +-0, a pole error shall occur, and tgamma(), tgammaf(), and tgammal() shall return +-HUGE_VAL, +-HUGE_VALF, and
       +-HUGE_VALL, respectively.

       If x is -Inf, a domain error shall occur, and either a NaN (if supported), or an implementation-defined  value  shall  be
       returned.

ERRORS
       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  inte-
       ger 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  inte-
       ger  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
       For IEEE Std 754-1985 double, overflow happens when 0 < x < 1/DBL_MAX, and 171.7 < x.

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

FUTURE DIRECTIONS
       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.

SEE ALSO
       feclearexcept(), fetestexcept(), lgamma(), 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, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    TGAMMA(3P)