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119 lines
3.6 KiB
Plaintext
119 lines
3.6 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "LGAMMA" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" lgamma
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.SH NAME
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lgamma, lgammaf, lgammal \- log gamma function
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.SH SYNOPSIS
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.LP
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\fB#include <math.h>
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.br
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.sp
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double lgamma(double\fP \fIx\fP\fB);
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.br
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float lgammaf(float\fP \fIx\fP\fB);
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.br
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long double lgammal(long double\fP \fIx\fP\fB);
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.br
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\fP
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.LP
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\fBextern int signgam; \fP
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\fB
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.br
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\fP
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.SH DESCRIPTION
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.LP
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These functions shall compute
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.sp
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.sp
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The argument \fIx\fP need not be a non-positive integer (Gamma(x)
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is defined over the reals,
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except the non-positive integers).
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.LP
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The sign of Gamma(x) is returned in the external integer \fIsigngam\fP.
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.LP
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These functions need not be reentrant. A function that is not required
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to be reentrant is not required to be thread-safe.
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.LP
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An application wishing to check for error situations should set \fIerrno\fP
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to zero and call
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\fIfeclearexcept\fP(FE_ALL_EXCEPT) before calling these functions.
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On return, if \fIerrno\fP is non-zero or
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\fIfetestexcept\fP(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
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is non-zero, an error has occurred.
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.SH RETURN VALUE
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.LP
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Upon successful completion, these functions shall return the logarithmic
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gamma of \fIx\fP.
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.LP
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If \fIx\fP is a non-positive integer, a pole error shall occur and
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\fIlgamma\fP(), \fIlgammaf\fP(), and \fIlgammal\fP()
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shall return +HUGE_VAL, +HUGE_VALF, and +HUGE_VALL, respectively.
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.LP
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If the correct value would cause overflow, a range error shall occur
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and \fIlgamma\fP(), \fIlgammaf\fP(), and \fIlgammal\fP()
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shall return \(+-HUGE_VAL, \(+-HUGE_VALF, and \(+-HUGE_VALL (having
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the same sign as the correct value),
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respectively.
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.LP
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If
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\fIx\fP is NaN, a NaN shall be returned.
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.LP
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If \fIx\fP is 1 or 2, +0 shall be returned.
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.LP
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If \fIx\fP is \(+-Inf, +Inf shall be returned.
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.SH ERRORS
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.LP
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These functions shall fail if:
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.TP 7
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Pole\ Error
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The \fIx\fP argument is a negative integer or zero.
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.LP
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If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
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then \fIerrno\fP shall be set to [ERANGE]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
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then the divide-by-zero floating-point exception shall be
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raised.
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.TP 7
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Range\ Error
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The result overflows.
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.LP
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If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
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then \fIerrno\fP shall be set to [ERANGE]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
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then the overflow floating-point exception shall be
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raised.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.LP
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None.
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.SH APPLICATION USAGE
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.LP
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On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling
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& MATH_ERREXCEPT) are independent of
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each other, but at least one of them must be non-zero.
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.SH RATIONALE
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.LP
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None.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIexp\fP() , \fIfeclearexcept\fP() , \fIfetestexcept\fP() , \fIisnan\fP()
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, the Base Definitions volume of
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IEEE\ Std\ 1003.1-2001, Section 4.18, Treatment of Error Conditions
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for
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Mathematical Functions, \fI<math.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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