#include "FEATURE/uwin"
#if !_UWIN || _lib_gamma
void _STUB_gamma(){}
#else
#ifndef lint
static char sccsid[] = "@(#)gamma.c 8.1 (Berkeley) 6/4/93";
#endif
#define gamma ______gamma
#include <math.h>
#include <errno.h>
#include "mathimpl.h"
#undef gamma
static double neg_gam __P((double));
static double small_gam __P((double));
static double smaller_gam __P((double));
static struct Double large_gam __P((double));
static struct Double ratfun_gam __P((double, double));
#define LEFT -.3955078125
#define x0 .461632144968362356785
#define a0_hi 0.88560319441088874992
#define a0_lo -.00000000000000004996427036469019695
#define P0 6.21389571821820863029017800727e-01
#define P1 2.65757198651533466104979197553e-01
#define P2 5.53859446429917461063308081748e-03
#define P3 1.38456698304096573887145282811e-03
#define P4 2.40659950032711365819348969808e-03
#define Q0 1.45019531250000000000000000000e+00
#define Q1 1.06258521948016171343454061571e+00
#define Q2 -2.07474561943859936441469926649e-01
#define Q3 -1.46734131782005422506287573015e-01
#define Q4 3.07878176156175520361557573779e-02
#define Q5 5.12449347980666221336054633184e-03
#define Q6 -1.76012741431666995019222898833e-03
#define Q7 9.35021023573788935372153030556e-05
#define Q8 6.13275507472443958924745652239e-06
#define lns2pi_hi 0.418945312500000
#define lns2pi_lo -.000006779295327258219670263595
#define Pa0 8.33333333333333148296162562474e-02
#define Pa1 -2.77777777774548123579378966497e-03
#define Pa2 7.93650778754435631476282786423e-04
#define Pa3 -5.95235082566672847950717262222e-04
#define Pa4 8.41428560346653702135821806252e-04
#define Pa5 -1.89773526463879200348872089421e-03
#define Pa6 5.69394463439411649408050664078e-03
#define Pa7 -1.44705562421428915453880392761e-02
static const double zero = 0., one = 1.0, tiny = 1e-300;
static int endian;
#if defined(vax) || defined(tahoe)
#define _IEEE 0
#define TRUNC(x) x = (double) (float) (x)
#else
#define _IEEE 1
#define TRUNC(x) *(((int *) &x) + endian) &= 0xf8000000
#define infnan(x) 0.0
#endif
extern double gamma(x)
double x;
{
struct Double u;
endian = (*(int *) &one) ? 1 : 0;
if (x >= 6) {
if(x > 171.63)
return(one/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)
if (!_IEEE) return (infnan(ERANGE));
else return (one/x);
one+1e-20;
return (one/x);
} else if (!finite(x)) {
if (_IEEE)
return (x*x);
else
return (infnan(EDOM));
} else
return (neg_gam(x));
}
static struct Double
large_gam(x)
double x;
{
double z, p;
struct Double t, u, v;
z = one/(x*x);
p = Pa0+z*(Pa1+z*(Pa2+z*(Pa3+z*(Pa4+z*(Pa5+z*(Pa6+z*Pa7))))));
p = p/x;
u = __log__D(x);
u.a -= one;
v.a = (x -= .5);
TRUNC(v.a);
v.b = x - v.a;
t.a = v.a*u.a;
t.b = v.b*u.a + x*u.b;
t.b += lns2pi_lo; t.b += p;
u.a = lns2pi_hi + t.b; u.a += t.a;
u.b = t.a - u.a;
u.b += lns2pi_hi; u.b += t.b;
return (u);
}
static double
small_gam(x)
double x;
{
double y, ym1, t;
struct Double yy, r;
y = x - one;
ym1 = y - one;
if (y <= 1.0 + (LEFT + x0)) {
yy = ratfun_gam(y - x0, 0);
return (yy.a + yy.b);
}
r.a = y;
TRUNC(r.a);
yy.a = r.a - one;
y = ym1;
yy.b = r.b = y - yy.a;
for (ym1 = y-one; ym1 > LEFT + x0; y = ym1--, yy.a--) {
t = r.a*yy.a;
r.b = r.a*yy.b + y*r.b;
r.a = t;
TRUNC(r.a);
r.b += (t - r.a);
}
yy = ratfun_gam(y - x0, 0);
y = r.b*(yy.a + yy.b) + r.a*yy.b;
y += yy.a*r.a;
return (y);
}
static double
smaller_gam(x)
double x;
{
double t, d;
struct Double r, xx;
if (x < x0 + LEFT) {
t = x, TRUNC(t);
d = (t+x)*(x-t);
t *= t;
xx.a = (t + x), TRUNC(xx.a);
xx.b = x - xx.a; xx.b += t; xx.b += d;
t = (one-x0); t += x;
d = (one-x0); d -= t; d += x;
x = xx.a + xx.b;
} else {
xx.a = x, TRUNC(xx.a);
xx.b = x - xx.a;
t = x - x0;
d = (-x0 -t); d += x;
}
r = ratfun_gam(t, d);
d = r.a/x, TRUNC(d);
r.a -= d*xx.a; r.a -= d*xx.b; r.a += r.b;
return (d + r.a/x);
}
static struct Double
ratfun_gam(z, c)
double z, c;
{
double p, q;
struct Double r, t;
q = Q0 +z*(Q1+z*(Q2+z*(Q3+z*(Q4+z*(Q5+z*(Q6+z*(Q7+z*Q8)))))));
p = P0 + z*(P1 + z*(P2 + z*(P3 + z*P4)));
p = p/q;
t.a = z, TRUNC(t.a);
t.b = (z - t.a) + c;
t.b *= (t.a + z);
q = (t.a *= t.a);
TRUNC(t.a);
t.b += (q - t.a);
r.a = p, TRUNC(r.a);
r.b = p - r.a;
t.b = t.b*p + t.a*r.b + a0_lo;
t.a *= r.a;
r.a = t.a + a0_hi, TRUNC(r.a);
r.b = ((a0_hi-r.a) + t.a) + t.b;
return (r);
}
static double
neg_gam(x)
double x;
{
int sgn = 1;
struct Double lg, lsine;
double y, z;
y = floor(x + .5);
if (y == x)
if(!_IEEE)
return (infnan(ERANGE));
else
return (one/zero);
z = fabs(x - y);
y = .5*ceil(x);
if (y == ceil(y))
sgn = -1;
if (z < .25)
z = sin(M_PI*z);
else
z = cos(M_PI*(0.5-z));
if (x < -170) {
if (x < -190)
return ((double)sgn*tiny*tiny);
y = one - x;
lg = large_gam(y);
lsine = __log__D(M_PI/z);
lg.a -= lsine.a;
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 = gamma(y);
else
y = -x*gamma(-x);
if (sgn < 0) y = -y;
return (M_PI / (y*z));
}
#endif