static double
neg_gam(double x)
{
int sgn = 1;
struct Double lg, lsine;
double y, z;
y = ceil(x);
if (y == x) /* Negative integer. */
if (_IEEE)
return ((x - x) / zero);
else
return (infnan(ERANGE));
z = y - x;
if (z > 0.5)
z = one - z;
y = 0.5 * y;
if (y == ceil(y))
sgn = -1;
if (z < .25)
z = sin(M_PI*z);
else
z = cos(M_PI*(0.5-z));
/* Special case: G(1-x) = Inf; G(x) may be nonzero. */
if (x < -170) {
if (x < -190)
return ((double)sgn*tiny*tiny);
y = one - x; /* exact: 128 < |x| < 255 */
lg = large_gam(y);
lsine = __log__D(M_PI/z); /* = TRUNC(log(u)) + small */
lg.a -= lsine.a; /* exact (opposite signs) */
lg.b -= lsine.b;
y = -(lg.a + lg.b);
z = (y + lg.a) + lg.b;
y = __exp__D(y, z);
if (sgn < 0) y = -y;
return (y);
}
y = one-x;
if (one-y == x)
y = tgamma(y);
else /* 1-x is inexact */
y = -x*tgamma(-x);
if (sgn < 0) y = -y;
return (M_PI / (y*z));
}
double
tgamma(double x)
{
struct Double u;
if (x >= 6) {
if(x > 171.63)
return (x / zero);
u = large_gam(x);
return(__exp__D(u.a, u.b));
} else if (x >= 1.0 + LEFT + x0)
return (small_gam(x));
else if (x > 1.e-17)
return (smaller_gam(x));
else if (x > -1.e-17) {
if (x != 0.0)
u.a = one - tiny; /* raise inexact */
return (one/x);
} else if (!finite(x))
return (x - x); /* x is NaN or -Inf */
else
return (neg_gam(x));
}
double
tgamma(double x)
{
struct Double u;
#if _IEEE
endian = (*(int *) &one) ? 1 : 0;
#endif
if (x >= 6) {
if(x > 171.63)
if (_IEEE)
return (x/zero);
else
return (infnan(ERANGE));
u = large_gam(x);
return(__exp__D(u.a, u.b));
} else if (x >= 1.0 + LEFT + x0)
return (small_gam(x));
else if (x > 1.e-17)
return (smaller_gam(x));
else if (x > -1.e-17) {
if (x == 0.0) {
if (!_IEEE)
return (infnan(ERANGE));
} else {
u.a = one - tiny; /* raise inexact */
}
return (one/x);
} else if (!finite(x)) {
if (_IEEE) /* x = NaN, -Inf */
return (x - x);
else
return (infnan(EDOM));
} else
return (neg_gam(x));
}
