LGAMMA(3)                 OpenBSD Programmer's Manual                LGAMMA(3)

NAME
     lgamma, lgammaf, tgamma, tgammaf - log gamma functions

SYNOPSIS
     #include <math.h>

     extern int signgam;

     double
     lgamma(double x);

     float
     lgammaf(float x);

     double
     tgamma(double x);

     float
     tgammaf(float x);

DESCRIPTION
     lgamma(x) returns ln||(x)|.

     The external integer signgam returns the sign of |(x).  The lgammaf()
     function is a single precision version of lgamma().

     The tgamma(x) and tgammaf(x) functions return |(x), with no effect on
     signgam.

IDIOSYNCRASIES
     Do not use the expression `signgam*exp(lgamma(x))' to compute g := |(x).
     Instead use a program like this (in C):

           lg = lgamma(x); g = signgam*exp(lg);

     Only after lgamma() has returned can signgam be correct.

     For arguments in its range, tgamma() is preferred, as for positive
     arguments it is accurate to within one unit in the last place.

RETURN VALUES
     lgamma() returns appropriate values unless an argument is out of range.
     Overflow will occur for sufficiently large positive values, and non-
     positive integers.  For large non-integer negative values, tgamma() will
     underflow.  On the VAX, the reserved operator is returned, and errno is
     set to ERANGE.

SEE ALSO
     infnan(3), math(3)

STANDARDS
     The lgamma(), lgammaf(), tgamma(), and tgammaf() functions are expected
     to conform to ISO/IEC 9899:1999 (``ISO C99'').

     gamma() and gammaf() are deprecated aliases for lgamma() and lgammaf(),
     respectively.

HISTORY
     The lgamma() function first appeared in 4.3BSD.  The tgamma() function
     first appeared in OpenBSD 4.4, and is based on the gamma() function that
     appeared in 4.4BSD as a function to compute |(x).

OpenBSD 4.9                      June 12, 2008                     OpenBSD 4.9