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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 (consult 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 sup-
       ported), 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  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.

       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,  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                           TGAMMA(3P)