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0dd5a5603e
Remove no longer needed explicit inclusion of sys/cdefs.h. PR: 276669 MFC after: 1 week
397 lines
9.7 KiB
C
397 lines
9.7 KiB
C
/*-
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* SPDX-License-Identifier: BSD-3-Clause
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*
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* Copyright (c) 1992, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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/*
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* The original code, FreeBSD's old svn r93211, contained the following
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* attribution:
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*
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* This code by P. McIlroy, Oct 1992;
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*
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* The financial support of UUNET Communications Services is greatfully
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* acknowledged.
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*
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* The algorithm remains, but the code has been re-arranged to facilitate
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* porting to other precisions.
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*/
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#include <float.h>
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#include "math.h"
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#include "math_private.h"
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/* Used in b_log.c and below. */
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struct Double {
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double a;
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double b;
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};
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#include "b_log.c"
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#include "b_exp.c"
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/*
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* The range is broken into several subranges. Each is handled by its
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* helper functions.
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*
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* x >= 6.0: large_gam(x)
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* 6.0 > x >= xleft: small_gam(x) where xleft = 1 + left + x0.
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* xleft > x > iota: smaller_gam(x) where iota = 1e-17.
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* iota > x > -itoa: Handle x near 0.
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* -iota > x : neg_gam
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*
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* Special values:
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* -Inf: return NaN and raise invalid;
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* negative integer: return NaN and raise invalid;
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* other x ~< 177.79: return +-0 and raise underflow;
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* +-0: return +-Inf and raise divide-by-zero;
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* finite x ~> 171.63: return +Inf and raise overflow;
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* +Inf: return +Inf;
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* NaN: return NaN.
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*
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* Accuracy: tgamma(x) is accurate to within
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* x > 0: error provably < 0.9ulp.
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* Maximum observed in 1,000,000 trials was .87ulp.
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* x < 0:
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* Maximum observed error < 4ulp in 1,000,000 trials.
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*/
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/*
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* Constants for large x approximation (x in [6, Inf])
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* (Accurate to 2.8*10^-19 absolute)
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*/
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static const double zero = 0.;
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static const volatile double tiny = 1e-300;
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/*
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* x >= 6
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*
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* Use the asymptotic approximation (Stirling's formula) adjusted fof
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* equal-ripples:
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*
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* log(G(x)) ~= (x-0.5)*(log(x)-1) + 0.5(log(2*pi)-1) + 1/x*P(1/(x*x))
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*
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* Keep extra precision in multiplying (x-.5)(log(x)-1), to avoid
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* premature round-off.
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*
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* Accurate to max(ulp(1/128) absolute, 2^-66 relative) error.
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*/
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static const double
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ln2pi_hi = 0.41894531250000000,
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ln2pi_lo = -6.7792953272582197e-6,
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Pa0 = 8.3333333333333329e-02, /* 0x3fb55555, 0x55555555 */
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Pa1 = -2.7777777777735404e-03, /* 0xbf66c16c, 0x16c145ec */
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Pa2 = 7.9365079044114095e-04, /* 0x3f4a01a0, 0x183de82d */
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Pa3 = -5.9523715464225254e-04, /* 0xbf438136, 0x0e681f62 */
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Pa4 = 8.4161391899445698e-04, /* 0x3f4b93f8, 0x21042a13 */
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Pa5 = -1.9065246069191080e-03, /* 0xbf5f3c8b, 0x357cb64e */
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Pa6 = 5.9047708485785158e-03, /* 0x3f782f99, 0xdaf5d65f */
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Pa7 = -1.6484018705183290e-02; /* 0xbf90e12f, 0xc4fb4df0 */
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static struct Double
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large_gam(double x)
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{
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double p, z, thi, tlo, xhi, xlo;
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struct Double u;
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z = 1 / (x * x);
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p = Pa0 + z * (Pa1 + z * (Pa2 + z * (Pa3 + z * (Pa4 + z * (Pa5 +
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z * (Pa6 + z * Pa7))))));
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p = p / x;
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u = __log__D(x);
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u.a -= 1;
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/* Split (x - 0.5) in high and low parts. */
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x -= 0.5;
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xhi = (float)x;
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xlo = x - xhi;
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/* Compute t = (x-.5)*(log(x)-1) in extra precision. */
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thi = xhi * u.a;
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tlo = xlo * u.a + x * u.b;
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/* Compute thi + tlo + ln2pi_hi + ln2pi_lo + p. */
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tlo += ln2pi_lo;
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tlo += p;
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u.a = ln2pi_hi + tlo;
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u.a += thi;
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u.b = thi - u.a;
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u.b += ln2pi_hi;
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u.b += tlo;
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return (u);
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}
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/*
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* Rational approximation, A0 + x * x * P(x) / Q(x), on the interval
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* [1.066.., 2.066..] accurate to 4.25e-19.
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*
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* Returns r.a + r.b = a0 + (z + c)^2 * p / q, with r.a truncated.
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*/
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static const double
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#if 0
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a0_hi = 8.8560319441088875e-1,
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a0_lo = -4.9964270364690197e-17,
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#else
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a0_hi = 8.8560319441088875e-01, /* 0x3fec56dc, 0x82a74aef */
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a0_lo = -4.9642368725563397e-17, /* 0xbc8c9deb, 0xaa64afc3 */
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#endif
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P0 = 6.2138957182182086e-1,
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P1 = 2.6575719865153347e-1,
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P2 = 5.5385944642991746e-3,
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P3 = 1.3845669830409657e-3,
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P4 = 2.4065995003271137e-3,
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Q0 = 1.4501953125000000e+0,
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Q1 = 1.0625852194801617e+0,
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Q2 = -2.0747456194385994e-1,
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Q3 = -1.4673413178200542e-1,
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Q4 = 3.0787817615617552e-2,
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Q5 = 5.1244934798066622e-3,
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Q6 = -1.7601274143166700e-3,
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Q7 = 9.3502102357378894e-5,
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Q8 = 6.1327550747244396e-6;
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static struct Double
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ratfun_gam(double z, double c)
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{
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double p, q, thi, tlo;
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struct Double r;
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q = Q0 + z * (Q1 + z * (Q2 + z * (Q3 + z * (Q4 + z * (Q5 +
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z * (Q6 + z * (Q7 + z * Q8)))))));
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p = P0 + z * (P1 + z * (P2 + z * (P3 + z * P4)));
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p = p / q;
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/* Split z into high and low parts. */
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thi = (float)z;
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tlo = (z - thi) + c;
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tlo *= (thi + z);
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/* Split (z+c)^2 into high and low parts. */
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thi *= thi;
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q = thi;
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thi = (float)thi;
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tlo += (q - thi);
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/* Split p/q into high and low parts. */
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r.a = (float)p;
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r.b = p - r.a;
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tlo = tlo * p + thi * r.b + a0_lo;
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thi *= r.a; /* t = (z+c)^2*(P/Q) */
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r.a = (float)(thi + a0_hi);
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r.b = ((a0_hi - r.a) + thi) + tlo;
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return (r); /* r = a0 + t */
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}
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/*
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* x < 6
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*
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* Use argument reduction G(x+1) = xG(x) to reach the range [1.066124,
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* 2.066124]. Use a rational approximation centered at the minimum
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* (x0+1) to ensure monotonicity.
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*
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* Good to < 1 ulp. (provably .90 ulp; .87 ulp on 1,000,000 runs.)
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* It also has correct monotonicity.
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*/
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static const double
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left = -0.3955078125, /* left boundary for rat. approx */
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x0 = 4.6163214496836236e-1; /* xmin - 1 */
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static double
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small_gam(double x)
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{
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double t, y, ym1;
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struct Double yy, r;
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y = x - 1;
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if (y <= 1 + (left + x0)) {
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yy = ratfun_gam(y - x0, 0);
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return (yy.a + yy.b);
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}
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r.a = (float)y;
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yy.a = r.a - 1;
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y = y - 1 ;
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r.b = yy.b = y - yy.a;
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/* Argument reduction: G(x+1) = x*G(x) */
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for (ym1 = y - 1; ym1 > left + x0; y = ym1--, yy.a--) {
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t = r.a * yy.a;
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r.b = r.a * yy.b + y * r.b;
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r.a = (float)t;
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r.b += (t - r.a);
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}
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/* Return r*tgamma(y). */
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yy = ratfun_gam(y - x0, 0);
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y = r.b * (yy.a + yy.b) + r.a * yy.b;
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y += yy.a * r.a;
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return (y);
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}
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/*
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* Good on (0, 1+x0+left]. Accurate to 1 ulp.
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*/
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static double
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smaller_gam(double x)
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{
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double d, rhi, rlo, t, xhi, xlo;
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struct Double r;
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if (x < x0 + left) {
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t = (float)x;
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d = (t + x) * (x - t);
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t *= t;
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xhi = (float)(t + x);
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xlo = x - xhi;
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xlo += t;
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xlo += d;
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t = 1 - x0;
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t += x;
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d = 1 - x0;
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d -= t;
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d += x;
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x = xhi + xlo;
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} else {
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xhi = (float)x;
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xlo = x - xhi;
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t = x - x0;
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d = - x0 - t;
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d += x;
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}
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r = ratfun_gam(t, d);
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d = (float)(r.a / x);
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r.a -= d * xhi;
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r.a -= d * xlo;
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r.a += r.b;
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return (d + r.a / x);
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}
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/*
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* x < 0
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*
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* Use reflection formula, G(x) = pi/(sin(pi*x)*x*G(x)).
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* At negative integers, return NaN and raise invalid.
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*/
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static double
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neg_gam(double x)
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{
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int sgn = 1;
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struct Double lg, lsine;
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double y, z;
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y = ceil(x);
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if (y == x) /* Negative integer. */
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return ((x - x) / zero);
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z = y - x;
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if (z > 0.5)
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z = 1 - z;
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y = y / 2;
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if (y == ceil(y))
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sgn = -1;
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if (z < 0.25)
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z = sinpi(z);
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else
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z = cospi(0.5 - z);
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/* Special case: G(1-x) = Inf; G(x) may be nonzero. */
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if (x < -170) {
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if (x < -190)
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return (sgn * tiny * tiny);
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y = 1 - x; /* exact: 128 < |x| < 255 */
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lg = large_gam(y);
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lsine = __log__D(M_PI / z); /* = TRUNC(log(u)) + small */
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lg.a -= lsine.a; /* exact (opposite signs) */
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lg.b -= lsine.b;
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y = -(lg.a + lg.b);
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z = (y + lg.a) + lg.b;
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y = __exp__D(y, z);
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if (sgn < 0) y = -y;
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return (y);
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}
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y = 1 - x;
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if (1 - y == x)
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y = tgamma(y);
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else /* 1-x is inexact */
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y = - x * tgamma(-x);
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if (sgn < 0) y = -y;
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return (M_PI / (y * z));
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}
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/*
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* xmax comes from lgamma(xmax) - emax * log(2) = 0.
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* static const float xmax = 35.040095f
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* static const double xmax = 171.624376956302725;
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* ld80: LD80C(0xdb718c066b352e20, 10, 1.75554834290446291689e+03L),
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* ld128: 1.75554834290446291700388921607020320e+03L,
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*
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* iota is a sloppy threshold to isolate x = 0.
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*/
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static const double xmax = 171.624376956302725;
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static const double iota = 0x1p-56;
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double
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tgamma(double x)
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{
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struct Double u;
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if (x >= 6) {
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if (x > xmax)
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return (x / zero);
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u = large_gam(x);
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return (__exp__D(u.a, u.b));
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}
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if (x >= 1 + left + x0)
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return (small_gam(x));
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if (x > iota)
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return (smaller_gam(x));
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if (x > -iota) {
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if (x != 0.)
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u.a = 1 - tiny; /* raise inexact */
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return (1 / x);
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}
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if (!isfinite(x))
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return (x - x); /* x is NaN or -Inf */
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return (neg_gam(x));
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}
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#if (LDBL_MANT_DIG == 53)
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__weak_reference(tgamma, tgammal);
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#endif
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