double
     tgamma(double x);

     long double
     tgammal(long double x);

     float
     tgamma(float x);

     double
     lgamma(double x);

     float
     lgamma(float x);

     double
     gamma(double x);

DESCRIPTION

     tgamma() calculates the gamma function of x.  lgamma() calculates the
     natural logorithm of the absolute value of the gamma function of x.
     gamma() is the same function as tgamma. Its use is deprecated.

SPECIAL VALUES

     tgamma(+-0) returns +-infinity and raises the "divide-by-zero" floating-
     point exception.

     tgamma(x) returns a NaN and raises the "invalid" floating-point exception
     if x is a negative integer.

     tgamma(-infinity) returns a NaN and raises the "invalid" floating-point
     exception.

     tgamma(+infinity) returns +infinity.

     tgamma(x) generates a domain error if x is a negative integer or if the
     result cannnot be respresented when x is 0.

     A range error may occur if the magnitude of x is too large or too small.

     gamma() has the same behavior as tgamma()

     lgamma(1) returns +0.

     lgamma(2) returns +0.

     lgamma(x) returns +infinity and raises the "divide-by-zero" floating-
     point exception if x is a negative integer or 0.

     lgamma(+-infinity) returns +infinity.