.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "TGAMMA" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" tgamma 
.SH NAME
tgamma, tgammaf, tgammal \- compute gamma() function
.SH SYNOPSIS
.LP
\fB#include <math.h>
.br
.sp
double tgamma(double\fP \fIx\fP\fB);
.br
float tgammaf(float\fP \fIx\fP\fB);
.br
long double tgammal(long double\fP \fIx\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
These functions shall compute the \fIgamma\fP() function of \fIx\fP.
.LP
An application wishing to check for error situations should set \fIerrno\fP
to zero and call
\fIfeclearexcept\fP(FE_ALL_EXCEPT) before calling these functions.
On return, if \fIerrno\fP is non-zero or
\fIfetestexcept\fP(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
is non-zero, an error has occurred.
.SH RETURN VALUE
.LP
Upon successful completion, these functions shall return \fIGamma\fP(
\fIx\fP).
.LP
If \fIx\fP is a negative integer, a domain error shall occur, and
either a NaN (if supported), or an implementation-defined
value shall be returned.
.LP
If the correct value would cause overflow, a range error shall occur
and \fItgamma\fP(), \fItgammaf\fP(), and \fItgammal\fP()
shall return \(+-HUGE_VAL, \(+-HUGE_VALF, or \(+-HUGE_VALL, respectively,
with the same sign as the correct value of
the function.
.LP
If
\fIx\fP is NaN, a NaN shall be returned.
.LP
If \fIx\fP is +Inf, \fIx\fP shall be returned.
.LP
If \fIx\fP is \(+-0, a pole error shall occur, and \fItgamma\fP(),
\fItgammaf\fP(), and \fItgammal\fP() shall return
\(+-HUGE_VAL, \(+-HUGE_VALF, and \(+-HUGE_VALL, respectively.
.LP
If \fIx\fP is -Inf, a domain error shall occur, and either a NaN (if
supported), or an implementation-defined value shall be
returned. 
.SH ERRORS
.LP
These functions shall fail if:
.TP 7
Domain\ Error
The value of \fIx\fP is a negative integer,   \ or \fIx\fP is -Inf.
.LP
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then \fIerrno\fP 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.
.TP 7
Pole\ Error
The value of \fIx\fP is zero. 
.LP
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then \fIerrno\fP 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. 
.br
.TP 7
Range\ Error
The value overflows. 
.LP
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then \fIerrno\fP 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.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
For IEEE\ Std\ 754-1985 \fBdouble\fP, overflow happens when 0 < \fIx\fP
< 1/DBL_MAX, and 171.7 <
\fIx\fP.
.LP
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.
.SH RATIONALE
.LP
This function is named \fItgamma\fP() in order to avoid conflicts
with the historical \fIgamma\fP() and \fIlgamma\fP() functions.
.SH FUTURE DIRECTIONS
.LP
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.
.SH SEE ALSO
.LP
\fIfeclearexcept\fP() , \fIfetestexcept\fP() , \fIlgamma\fP() , the
Base Definitions volume of IEEE\ Std\ 1003.1-2001, Section 4.18, Treatment
of Error Conditions for Mathematical Functions, \fI<math.h>\fP
.SH 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 .