minix/lib/libm/noieee_src/n_gamma.c
Ben Gras 2fe8fb192f Full switch to clang/ELF. Drop ack. Simplify.
There is important information about booting non-ack images in
docs/UPDATING. ack/aout-format images can't be built any more, and
booting clang/ELF-format ones is a little different. Updating to the
new boot monitor is recommended.

Changes in this commit:

	. drop boot monitor -> allowing dropping ack support
	. facility to copy ELF boot files to /boot so that old boot monitor
	  can still boot fairly easily, see UPDATING
	. no more ack-format libraries -> single-case libraries
	. some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases
	. drop several ack toolchain commands, but not all support
	  commands (e.g. aal is gone but acksize is not yet).
	. a few libc files moved to netbsd libc dir
	. new /bin/date as minix date used code in libc/
	. test compile fix
	. harmonize includes
	. /usr/lib is no longer special: without ack, /usr/lib plays no
	  kind of special bootstrapping role any more and bootstrapping
	  is done exclusively through packages, so releases depend even
	  less on the state of the machine making them now.
	. rename nbsd_lib* to lib*
	. reduce mtree
2012-02-14 14:52:02 +01:00

333 lines
9 KiB
C

/* $NetBSD: n_gamma.c,v 1.6 2006/11/24 21:15:54 wiz Exp $ */
/*-
* Copyright (c) 1992, 1993
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#ifndef lint
#if 0
static char sccsid[] = "@(#)gamma.c 8.1 (Berkeley) 6/4/93";
#endif
#endif /* not lint */
/*
* This code by P. McIlroy, Oct 1992;
*
* The financial support of UUNET Communications Services is gratefully
* acknowledged.
*/
#include <math.h>
#include "mathimpl.h"
#include <errno.h>
/* METHOD:
* x < 0: Use reflection formula, G(x) = pi/(sin(pi*x)*x*G(x))
* At negative integers, return +Inf, and set errno.
*
* x < 6.5:
* Use argument reduction G(x+1) = xG(x) to reach the
* range [1.066124,2.066124]. Use a rational
* approximation centered at the minimum (x0+1) to
* ensure monotonicity.
*
* x >= 6.5: Use the asymptotic approximation (Stirling's formula)
* adjusted for equal-ripples:
*
* log(G(x)) ~= (x-.5)*(log(x)-1) + .5(log(2*pi)-1) + 1/x*P(1/(x*x))
*
* Keep extra precision in multiplying (x-.5)(log(x)-1), to
* avoid premature round-off.
*
* Special values:
* non-positive integer: Set overflow trap; return +Inf;
* x > 171.63: Set overflow trap; return +Inf;
* NaN: Set invalid trap; return NaN
*
* Accuracy: Gamma(x) is accurate to within
* x > 0: error provably < 0.9ulp.
* Maximum observed in 1,000,000 trials was .87ulp.
* x < 0:
* Maximum observed error < 4ulp in 1,000,000 trials.
*/
static double neg_gam (double);
static double small_gam (double);
static double smaller_gam (double);
static struct Double large_gam (double);
static struct Double ratfun_gam (double, double);
/*
* Rational approximation, A0 + x*x*P(x)/Q(x), on the interval
* [1.066.., 2.066..] accurate to 4.25e-19.
*/
#define LEFT -.3955078125 /* left boundary for rat. approx */
#define x0 .461632144968362356785 /* xmin - 1 */
#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
/*
* Constants for large x approximation (x in [6, Inf])
* (Accurate to 2.8*10^-19 absolute)
*/
#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;
/*
* TRUNC sets trailing bits in a floating-point number to zero.
* is a temporary variable.
*/
#if defined(__vax__) || defined(tahoe)
#define _IEEE 0
#define TRUNC(x) x = (double) (float) (x)
#else
static int endian;
#define _IEEE 1
#define TRUNC(x) *(((int *) &x) + endian) &= 0xf8000000
#define infnan(x) 0.0
#endif
double
gamma(x)
double x;
{
double b;
struct Double u;
#if _IEEE
int endian = (*(int *) &one) ? 1 : 0;
#endif
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);
}
b =one+1e-20; /* Raise inexact flag. ??? -ragge */
return (one/x);
} else if (!finite(x)) {
if (_IEEE) /* x = NaN, -Inf */
return (x*x);
else
return (infnan(EDOM));
} else
return (neg_gam(x));
}
/*
* Accurate to max(ulp(1/128) absolute, 2^-66 relative) error.
*/
static struct Double
large_gam(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 = (x-.5)*(log(x)-1) */
t.b = v.b*u.a + x*u.b;
/* return t.a + t.b + lns2pi_hi + lns2pi_lo + p */
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);
}
/*
* Good to < 1 ulp. (provably .90 ulp; .87 ulp on 1,000,000 runs.)
* It also has correct monotonicity.
*/
static double
small_gam(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;
/* Argument reduction: G(x+1) = x*G(x) */
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);
}
/* Return r*gamma(y). */
yy = ratfun_gam(y - x0, 0);
y = r.b*(yy.a + yy.b) + r.a*yy.b;
y += yy.a*r.a;
return (y);
}
/*
* Good on (0, 1+x0+LEFT]. Accurate to 1ulp.
*/
static double
smaller_gam(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);
}
/*
* returns (z+c)^2 * P(z)/Q(z) + a0
*/
static struct Double
ratfun_gam(double z, double 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)));
/* return r.a + r.b = a0 + (z+c)^2*p/q, with r.a truncated to 26 bits. */
p = p/q;
t.a = z, TRUNC(t.a); /* t ~= z + c */
t.b = (z - t.a) + c;
t.b *= (t.a + z);
q = (t.a *= t.a); /* t = (z+c)^2 */
TRUNC(t.a);
t.b += (q - t.a);
r.a = p, TRUNC(r.a); /* r = P/Q */
r.b = p - r.a;
t.b = t.b*p + t.a*r.b + a0_lo;
t.a *= r.a; /* t = (z+c)^2*(P/Q) */
r.a = t.a + a0_hi, TRUNC(r.a);
r.b = ((a0_hi-r.a) + t.a) + t.b;
return (r); /* r = a0 + t */
}
static double
neg_gam(double x)
{
int sgn = 1;
struct Double lg, lsine;
double y, z;
y = floor(x + .5);
if (y == x) { /* Negative integer. */
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));
/* 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 = gamma(y);
else /* 1-x is inexact */
y = -x*gamma(-x);
if (sgn < 0) y = -y;
return (M_PI / (y*z));
}