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lgammad32.c

/* Natural logarithm of gamma function

   Copyright (C) 2001 Stephen L. Moshier <moshier@na-net.ornl.gov>
   Copyright (C) 2006 IBM Corporation.
   Copyright (C) 2001, 2007, 2009 Free Software Foundation, Inc.

   This file is part of the Decimal Floating Point C Library.

   Author(s): Joseph Kerian <jkerian@us.ibm.com>

   The Decimal Floating Point C Library is free software; you can
   redistribute it and/or modify it under the terms of the GNU Lesser
   General Public License version 2.1.

   The Decimal Floating Point C Library is distributed in the hope that
   it will be useful, but WITHOUT ANY WARRANTY; without even the implied
   warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
   the GNU Lesser General Public License version 2.1 for more details.

   You should have received a copy of the GNU Lesser General Public
   License version 2.1 along with the Decimal Floating Point C Library;
   if not, write to the Free Software Foundation, Inc., 59 Temple Place,
   Suite 330, Boston, MA 02111-1307 USA.

   Please see libdfp/COPYING.txt for more information.  */

#ifndef _DECIMAL_SIZE
#  include <decimal32.h>
#  define _DECIMAL_SIZE 32
#endif

#include <decContext.h>
#include <decNumber.h>
#include <dfp/math.h>
#include <float.h>
#include <errno.h>

#define FUNCTION_NAME lgamma

/* Adapted for libdfp from glibc in 2006 and donated to the FSF in 2007.
 *
 * lgammad32
 *
 *      Natural logarithm of gamma function
 *
 *
 *
 * SYNOPSIS:
 *
 * _Decimal128 x, y, lgamma32();
 * extern int sgngam;
 *
 * y = lgammad32(x);
 *
 *
 *
 * DESCRIPTION:
 *
 * Returns the base e (2.718...) logarithm of the absolute
 * value of the gamma function of the argument.
 * The sign (+1 or -1) of the gamma function is returned in a
 * global (extern) variable named sgngam.
 *
 * The positive domain is partitioned into numerous segments for approximation.
 * For x > 10,
 *   log gamma(x) = (x - 0.5) log(x) - x + log sqrt(2 pi) + 1/x R(1/x^2)
 * Near the minimum at x = x0 = 1.46... the approximation is
 *   log gamma(x0 + z) = log gamma(x0) + z^2 P(z)/Q(z)
 * for small z.
 * Elsewhere between 0 and 10,
 *   log gamma(n + z) = log gamma(n) + z P(z)/Q(z)
 * for various selected n and small z.
 *
 * The cosecant reflection formula is employed for negative arguments.
 *
 *
 *
 * ACCURACY:
 *
 *
 * arithmetic      domain        # trials     peak         rms
 *                                            Relative error:
 *    IEEE         10, 30         100000     3.9e-34     9.8e-35
 *    IEEE          0, 10         100000     3.8e-34     5.3e-35
 *                                            Absolute error:
 *    IEEE         -10, 0         100000     8.0e-34     8.0e-35
 *    IEEE         -30, -10       100000     4.4e-34     1.0e-34
 *    IEEE        -100, 100       100000                 1.0e-34
 *
 * The absolute error criterion is the same as relative error
 * when the function magnitude is greater than one but it is absolute
 * when the magnitude is less than one.
 *
 */

#include <dfpmacro.h>
#include <ieee754r_private.h>

static const _Decimal128 PIDL = 3.1415926535897932384626433832795028841972E0DL;
static const _Decimal128 MAXDLGM = 1.0485738685148938358098967157129705071571E4928DL;
static const _Decimal128 one = 1.0DL;
static const _Decimal128 zero = 0.0DL;
static const _Decimal128 huge = 1.0e4000DL;

/* log gamma(x) = ( x - 0.5 ) * log(x) - x + DLS2PI + 1/x P(1/x^2)
   1/x <= 0.0741 (x >= 13.495...)
   Peak relative error 1.5e-36  */
static const _Decimal128 ls2pi = 9.1893853320467274178032973640561763986140E-1DL;
#define NRASY 12
static const _Decimal128 RASY[NRASY + 1] =
{
  8.333333333333333333333333333310437112111E-2DL,
 -2.777777777777777777777774789556228296902E-3DL,
  7.936507936507936507795933938448586499183E-4DL,
 -5.952380952380952041799269756378148574045E-4DL,
  8.417508417507928904209891117498524452523E-4DL,
 -1.917526917481263997778542329739806086290E-3DL,
  6.410256381217852504446848671499409919280E-3DL,
 -2.955064066900961649768101034477363301626E-2DL,
  1.796402955865634243663453415388336954675E-1DL,
 -1.391522089007758553455753477688592767741E0DL,
  1.326130089598399157988112385013829305510E1DL,
 -1.420412699593782497803472576479997819149E2DL,
  1.218058922427762808938869872528846787020E3DL
};


/* log gamma(x+13) = log gamma(13) +  x P(x)/Q(x)
   -0.5 <= x <= 0.5
   12.5 <= x+13 <= 13.5
   Peak relative error 1.1e-36  */
static const _Decimal128 lgam13a = 1.9987213134765625E1DL;
static const _Decimal128 lgam13b = 1.3608962611495173623870550785125024484248E-6DL;
#define NRN13 7
static const _Decimal128 RN13[NRN13 + 1] =
{
  8.591478354823578150238226576156275285700E11DL,
  2.347931159756482741018258864137297157668E11DL,
  2.555408396679352028680662433943000804616E10DL,
  1.408581709264464345480765758902967123937E9DL,
  4.126759849752613822953004114044451046321E7DL,
  6.133298899622688505854211579222889943778E5DL,
  3.929248056293651597987893340755876578072E3DL,
  6.850783280018706668924952057996075215223E0DL
};
#define NRD13 6
static const _Decimal128 RD13[NRD13 + 1] =
{
  3.401225382297342302296607039352935541669E11DL,
  8.756765276918037910363513243563234551784E10DL,
  8.873913342866613213078554180987647243903E9DL,
  4.483797255342763263361893016049310017973E8DL,
  1.178186288833066430952276702931512870676E7DL,
  1.519928623743264797939103740132278337476E5DL,
  7.989298844938119228411117593338850892311E2DL
 /* 1.0E0DL */
};


/* log gamma(x+12) = log gamma(12) +  x P(x)/Q(x)
   -0.5 <= x <= 0.5
   11.5 <= x+12 <= 12.5
   Peak relative error 4.1e-36  */
static const _Decimal128 lgam12a = 1.75023040771484375E1DL;
static const _Decimal128 lgam12b = 3.7687254483392876529072161996717039575982E-6DL;
#define NRN12 7
static const _Decimal128 RN12[NRN12 + 1] =
{
  4.709859662695606986110997348630997559137E11DL,
  1.398713878079497115037857470168777995230E11DL,
  1.654654931821564315970930093932954900867E10DL,
  9.916279414876676861193649489207282144036E8DL,
  3.159604070526036074112008954113411389879E7DL,
  5.109099197547205212294747623977502492861E5DL,
  3.563054878276102790183396740969279826988E3DL,
  6.769610657004672719224614163196946862747E0DL
};
#define NRD12 6
static const _Decimal128 RD12[NRD12 + 1] =
{
  1.928167007860968063912467318985802726613E11DL,
  5.383198282277806237247492369072266389233E10DL,
  5.915693215338294477444809323037871058363E9DL,
  3.241438287570196713148310560147925781342E8DL,
  9.236680081763754597872713592701048455890E6DL,
  1.292246897881650919242713651166596478850E5DL,
  7.366532445427159272584194816076600211171E2DL
 /* 1.0E0DL */
};


/* log gamma(x+11) = log gamma(11) +  x P(x)/Q(x)
   -0.5 <= x <= 0.5
   10.5 <= x+11 <= 11.5
   Peak relative error 1.8e-35  */
static const _Decimal128 lgam11a = 1.5104400634765625E1DL;
static const _Decimal128 lgam11b = 1.1938309890295225709329251070371882250744E-5DL;
#define NRN11 7
static const _Decimal128 RN11[NRN11 + 1] =
{
  2.446960438029415837384622675816736622795E11DL,
  7.955444974446413315803799763901729640350E10DL,
  1.030555327949159293591618473447420338444E10DL,
  6.765022131195302709153994345470493334946E8DL,
  2.361892792609204855279723576041468347494E7DL,
  4.186623629779479136428005806072176490125E5DL,
  3.202506022088912768601325534149383594049E3DL,
  6.681356101133728289358838690666225691363E0DL
};
#define NRD11 6
static const _Decimal128 RD11[NRD11 + 1] =
{
  1.040483786179428590683912396379079477432E11DL,
  3.172251138489229497223696648369823779729E10DL,
  3.806961885984850433709295832245848084614E9DL,
  2.278070344022934913730015420611609620171E8DL,
  7.089478198662651683977290023829391596481E6DL,
  1.083246385105903533237139380509590158658E5DL,
  6.744420991491385145885727942219463243597E2DL
 /* 1.0E0DL */
};


/* log gamma(x+10) = log gamma(10) +  x P(x)/Q(x)
   -0.5 <= x <= 0.5
   9.5 <= x+10 <= 10.5
   Peak relative error 5.4e-37  */
static const _Decimal128 lgam10a = 1.280181884765625E1DL;
static const _Decimal128 lgam10b = 8.6324252196112077178745667061642811492557E-6DL;
#define NRN10 7
static const _Decimal128 RN10[NRN10 + 1] =
{
  -1.239059737177249934158597996648808363783E14DL,
  -4.725899566371458992365624673357356908719E13DL,
  -7.283906268647083312042059082837754850808E12DL,
  -5.802855515464011422171165179767478794637E11DL,
  -2.532349691157548788382820303182745897298E10DL,
  -5.884260178023777312587193693477072061820E8DL,
  -6.437774864512125749845840472131829114906E6DL,
  -2.350975266781548931856017239843273049384E4DL
};
#define NRD10 7
static const _Decimal128 RD10[NRD10 + 1] =
{
  -5.502645997581822567468347817182347679552E13DL,
  -1.970266640239849804162284805400136473801E13DL,
  -2.819677689615038489384974042561531409392E12DL,
  -2.056105863694742752589691183194061265094E11DL,
  -8.053670086493258693186307810815819662078E9DL,
  -1.632090155573373286153427982504851867131E8DL,
  -1.483575879240631280658077826889223634921E6DL,
  -4.002806669713232271615885826373550502510E3DL
 /* 1.0E0DL */
};


/* log gamma(x+9) = log gamma(9) +  x P(x)/Q(x)
   -0.5 <= x <= 0.5
   8.5 <= x+9 <= 9.5
   Peak relative error 3.6e-36  */
static const _Decimal128 lgam9a = 1.06045989990234375E1DL;
static const _Decimal128 lgam9b = 3.9037218127284172274007216547549861681400E-6DL;
#define NRN9 7
static const _Decimal128 RN9[NRN9 + 1] =
{
  -4.936332264202687973364500998984608306189E13DL,
  -2.101372682623700967335206138517766274855E13DL,
  -3.615893404644823888655732817505129444195E12DL,
  -3.217104993800878891194322691860075472926E11DL,
  -1.568465330337375725685439173603032921399E10DL,
  -4.073317518162025744377629219101510217761E8DL,
  -4.983232096406156139324846656819246974500E6DL,
  -2.036280038903695980912289722995505277253E4DL
};
#define NRD9 7
static const _Decimal128 RD9[NRD9 + 1] =
{
  -2.306006080437656357167128541231915480393E13DL,
  -9.183606842453274924895648863832233799950E12DL,
  -1.461857965935942962087907301194381010380E12DL,
  -1.185728254682789754150068652663124298303E11DL,
  -5.166285094703468567389566085480783070037E9DL,
  -1.164573656694603024184768200787835094317E8DL,
  -1.177343939483908678474886454113163527909E6DL,
  -3.529391059783109732159524500029157638736E3DL
  /* 1.0E0DL */
};


/* log gamma(x+8) = log gamma(8) +  x P(x)/Q(x)
   -0.5 <= x <= 0.5
   7.5 <= x+8 <= 8.5
   Peak relative error 2.4e-37  */
static const _Decimal128 lgam8a = 8.525146484375E0DL;
static const _Decimal128 lgam8b = 1.4876690414300165531036347125050759667737E-5DL;
#define NRN8 8
static const _Decimal128 RN8[NRN8 + 1] =
{
  6.600775438203423546565361176829139703289E11DL,
  3.406361267593790705240802723914281025800E11DL,
  7.222460928505293914746983300555538432830E10DL,
  8.102984106025088123058747466840656458342E9DL,
  5.157620015986282905232150979772409345927E8DL,
  1.851445288272645829028129389609068641517E7DL,
  3.489261702223124354745894067468953756656E5DL,
  2.892095396706665774434217489775617756014E3DL,
  6.596977510622195827183948478627058738034E0DL
};
#define NRD8 7
static const _Decimal128 RD8[NRD8 + 1] =
{
  3.274776546520735414638114828622673016920E11DL,
  1.581811207929065544043963828487733970107E11DL,
  3.108725655667825188135393076860104546416E10DL,
  3.193055010502912617128480163681842165730E9DL,
  1.830871482669835106357529710116211541839E8DL,
  5.790862854275238129848491555068073485086E6DL,
  9.305213264307921522842678835618803553589E4DL,
  6.216974105861848386918949336819572333622E2DL
  /* 1.0E0DL */
};


/* log gamma(x+7) = log gamma(7) +  x P(x)/Q(x)
   -0.5 <= x <= 0.5
   6.5 <= x+7 <= 7.5
   Peak relative error 3.2e-36  */
static const _Decimal128 lgam7a = 6.5792388916015625E0DL;
static const _Decimal128 lgam7b = 1.2320408538495060178292903945321122583007E-5DL;
#define NRN7 8
static const _Decimal128 RN7[NRN7 + 1] =
{
  2.065019306969459407636744543358209942213E11DL,
  1.226919919023736909889724951708796532847E11DL,
  2.996157990374348596472241776917953749106E10DL,
  3.873001919306801037344727168434909521030E9DL,
  2.841575255593761593270885753992732145094E8DL,
  1.176342515359431913664715324652399565551E7DL,
  2.558097039684188723597519300356028511547E5DL,
  2.448525238332609439023786244782810774702E3DL,
  6.460280377802030953041566617300902020435E0DL
};
#define NRD7 7
static const _Decimal128 RD7[NRD7 + 1] =
{
  1.102646614598516998880874785339049304483E11DL,
  6.099297512712715445879759589407189290040E10DL,
  1.372898136289611312713283201112060238351E10DL,
  1.615306270420293159907951633566635172343E9DL,
  1.061114435798489135996614242842561967459E8DL,
  3.845638971184305248268608902030718674691E6DL,
  7.081730675423444975703917836972720495507E4DL,
  5.423122582741398226693137276201344096370E2DL
  /* 1.0E0DL */
};


/* log gamma(x+6) = log gamma(6) +  x P(x)/Q(x)
   -0.5 <= x <= 0.5
   5.5 <= x+6 <= 6.5
   Peak relative error 6.2e-37  */
static const _Decimal128 lgam6a = 4.7874908447265625E0DL;
static const _Decimal128 lgam6b = 8.9805548349424770093452324304839959231517E-7DL;
#define NRN6 8
static const _Decimal128 RN6[NRN6 + 1] =
{
  -3.538412754670746879119162116819571823643E13DL,
  -2.613432593406849155765698121483394257148E13DL,
  -8.020670732770461579558867891923784753062E12DL,
  -1.322227822931250045347591780332435433420E12DL,
  -1.262809382777272476572558806855377129513E11DL,
  -7.015006277027660872284922325741197022467E9DL,
  -2.149320689089020841076532186783055727299E8DL,
  -3.167210585700002703820077565539658995316E6DL,
  -1.576834867378554185210279285358586385266E4DL
};
#define NRD6 8
static const _Decimal128 RD6[NRD6 + 1] =
{
  -2.073955870771283609792355579558899389085E13DL,
  -1.421592856111673959642750863283919318175E13DL,
  -4.012134994918353924219048850264207074949E12DL,
  -6.013361045800992316498238470888523722431E11DL,
  -5.145382510136622274784240527039643430628E10DL,
  -2.510575820013409711678540476918249524123E9DL,
  -6.564058379709759600836745035871373240904E7DL,
  -7.861511116647120540275354855221373571536E5DL,
  -2.821943442729620524365661338459579270561E3DL
  /* 1.0E0DL */
};


/* log gamma(x+5) = log gamma(5) +  x P(x)/Q(x)
   -0.5 <= x <= 0.5
   4.5 <= x+5 <= 5.5
   Peak relative error 3.4e-37  */
static const _Decimal128 lgam5a = 3.17803955078125E0DL;
static const _Decimal128 lgam5b = 1.4279566695619646941601297055408873990961E-5DL;
#define NRN5 9
static const _Decimal128 RN5[NRN5 + 1] =
{
  2.010952885441805899580403215533972172098E11DL,
  1.916132681242540921354921906708215338584E11DL,
  7.679102403710581712903937970163206882492E10DL,
  1.680514903671382470108010973615268125169E10DL,
  2.181011222911537259440775283277711588410E9DL,
  1.705361119398837808244780667539728356096E8DL,
  7.792391565652481864976147945997033946360E6DL,
  1.910741381027985291688667214472560023819E5DL,
  2.088138241893612679762260077783794329559E3DL,
  6.330318119566998299106803922739066556550E0DL
};
#define NRD5 8
static const _Decimal128 RD5[NRD5 + 1] =
{
  1.335189758138651840605141370223112376176E11DL,
  1.174130445739492885895466097516530211283E11DL,
  4.308006619274572338118732154886328519910E10DL,
  8.547402888692578655814445003283720677468E9DL,
  9.934628078575618309542580800421370730906E8DL,
  6.847107420092173812998096295422311820672E7DL,
  2.698552646016599923609773122139463150403E6DL,
  5.526516251532464176412113632726150253215E4DL,
  4.772343321713697385780533022595450486932E2DL
  /* 1.0E0DL */
};


/* log gamma(x+4) = log gamma(4) +  x P(x)/Q(x)
   -0.5 <= x <= 0.5
   3.5 <= x+4 <= 4.5
   Peak relative error 6.7e-37  */
static const _Decimal128 lgam4a = 1.791748046875E0DL;
static const _Decimal128 lgam4b = 1.1422353055000812477358380702272722990692E-5DL;
#define NRN4 9
static const _Decimal128 RN4[NRN4 + 1] =
{
  -1.026583408246155508572442242188887829208E13DL,
  -1.306476685384622809290193031208776258809E13DL,
  -7.051088602207062164232806511992978915508E12DL,
  -2.100849457735620004967624442027793656108E12DL,
  -3.767473790774546963588549871673843260569E11DL,
  -4.156387497364909963498394522336575984206E10DL,
  -2.764021460668011732047778992419118757746E9DL,
  -1.036617204107109779944986471142938641399E8DL,
  -1.895730886640349026257780896972598305443E6DL,
  -1.180509051468390914200720003907727988201E4DL
};
#define NRD4 9
static const _Decimal128 RD4[NRD4 + 1] =
{
  -8.172669122056002077809119378047536240889E12DL,
  -9.477592426087986751343695251801814226960E12DL,
  -4.629448850139318158743900253637212801682E12DL,
  -1.237965465892012573255370078308035272942E12DL,
  -1.971624313506929845158062177061297598956E11DL,
  -1.905434843346570533229942397763361493610E10DL,
  -1.089409357680461419743730978512856675984E9DL,
  -3.416703082301143192939774401370222822430E7DL,
  -4.981791914177103793218433195857635265295E5DL,
  -2.192507743896742751483055798411231453733E3DL
  /* 1.0E0DL */
};


/* log gamma(x+3) = log gamma(3) +  x P(x)/Q(x)
   -0.25 <= x <= 0.5
   2.75 <= x+3 <= 3.5
   Peak relative error 6.0e-37  */
static const _Decimal128 lgam3a = 6.93145751953125E-1DL;
static const _Decimal128 lgam3b = 1.4286068203094172321214581765680755001344E-6DL;

#define NRN3 9
static const _Decimal128 RN3[NRN3 + 1] =
{
  -4.813901815114776281494823863935820876670E11DL,
  -8.425592975288250400493910291066881992620E11DL,
  -6.228685507402467503655405482985516909157E11DL,
  -2.531972054436786351403749276956707260499E11DL,
  -6.170200796658926701311867484296426831687E10DL,
  -9.211477458528156048231908798456365081135E9DL,
  -8.251806236175037114064561038908691305583E8DL,
  -4.147886355917831049939930101151160447495E7DL,
  -1.010851868928346082547075956946476932162E6DL,
  -8.333374463411801009783402800801201603736E3DL
};
#define NRD3 9
static const _Decimal128 RD3[NRD3 + 1] =
{
  -5.216713843111675050627304523368029262450E11DL,
  -8.014292925418308759369583419234079164391E11DL,
  -5.180106858220030014546267824392678611990E11DL,
  -1.830406975497439003897734969120997840011E11DL,
  -3.845274631904879621945745960119924118925E10DL,
  -4.891033385370523863288908070309417710903E9DL,
  -3.670172254411328640353855768698287474282E8DL,
  -1.505316381525727713026364396635522516989E7DL,
  -2.856327162923716881454613540575964890347E5DL,
  -1.622140448015769906847567212766206894547E3DL
  /* 1.0E0DL */
};


/* log gamma(x+2.5) = log gamma(2.5) +  x P(x)/Q(x)
   -0.125 <= x <= 0.25
   2.375 <= x+2.5 <= 2.75  */
static const _Decimal128 lgam2r5a = 2.8466796875E-1DL;
static const _Decimal128 lgam2r5b = 1.4901722919159632494669682701924320137696E-5DL;
#define NRN2r5 8
static const _Decimal128 RN2r5[NRN2r5 + 1] =
{
  -4.676454313888335499356699817678862233205E9DL,
  -9.361888347911187924389905984624216340639E9DL,
  -7.695353600835685037920815799526540237703E9DL,
  -3.364370100981509060441853085968900734521E9DL,
  -8.449902011848163568670361316804900559863E8DL,
  -1.225249050950801905108001246436783022179E8DL,
  -9.732972931077110161639900388121650470926E6DL,
  -3.695711763932153505623248207576425983573E5DL,
  -4.717341584067827676530426007495274711306E3DL
};
#define NRD2r5 8
static const _Decimal128 RD2r5[NRD2r5 + 1] =
{
  -6.650657966618993679456019224416926875619E9DL,
  -1.099511409330635807899718829033488771623E10DL,
  -7.482546968307837168164311101447116903148E9DL,
  -2.702967190056506495988922973755870557217E9DL,
  -5.570008176482922704972943389590409280950E8DL,
  -6.536934032192792470926310043166993233231E7DL,
  -4.101991193844953082400035444146067511725E6DL,
  -1.174082735875715802334430481065526664020E5DL,
  -9.932840389994157592102947657277692978511E2DL
  /* 1.0E0DL */
};


/* log gamma(x+2) = x P(x)/Q(x)
   -0.125 <= x <= +0.375
   1.875 <= x+2 <= 2.375
   Peak relative error 4.6e-36  */
#define NRN2 9
static const _Decimal128 RN2[NRN2 + 1] =
{
  -3.716661929737318153526921358113793421524E9DL,
  -1.138816715030710406922819131397532331321E10DL,
  -1.421017419363526524544402598734013569950E10DL,
  -9.510432842542519665483662502132010331451E9DL,
  -3.747528562099410197957514973274474767329E9DL,
  -8.923565763363912474488712255317033616626E8DL,
  -1.261396653700237624185350402781338231697E8DL,
  -9.918402520255661797735331317081425749014E6DL,
  -3.753996255897143855113273724233104768831E5DL,
  -4.778761333044147141559311805999540765612E3DL
};
#define NRD2 9
static const _Decimal128 RD2[NRD2 + 1] =
{
  -8.790916836764308497770359421351673950111E9DL,
  -2.023108608053212516399197678553737477486E10DL,
  -1.958067901852022239294231785363504458367E10DL,
  -1.035515043621003101254252481625188704529E10DL,
  -3.253884432621336737640841276619272224476E9DL,
  -6.186383531162456814954947669274235815544E8DL,
  -6.932557847749518463038934953605969951466E7DL,
  -4.240731768287359608773351626528479703758E6DL,
  -1.197343995089189188078944689846348116630E5DL,
  -1.004622911670588064824904487064114090920E3DL
/* 1.0E0 */
};


/* log gamma(x+1.75) = log gamma(1.75) +  x P(x)/Q(x)
   -0.125 <= x <= +0.125
   1.625 <= x+1.75 <= 1.875
   Peak relative error 9.2e-37 */
static const _Decimal128 lgam1r75a = -8.441162109375E-2DL;
static const _Decimal128 lgam1r75b = 1.0500073264444042213965868602268256157604E-5DL;
#define NRN1r75 8
static const _Decimal128 RN1r75[NRN1r75 + 1] =
{
  -5.221061693929833937710891646275798251513E7DL,
  -2.052466337474314812817883030472496436993E8DL,
  -2.952718275974940270675670705084125640069E8DL,
  -2.132294039648116684922965964126389017840E8DL,
  -8.554103077186505960591321962207519908489E7DL,
  -1.940250901348870867323943119132071960050E7DL,
  -2.379394147112756860769336400290402208435E6DL,
  -1.384060879999526222029386539622255797389E5DL,
  -2.698453601378319296159355612094598695530E3DL
};
#define NRD1r75 8
static const _Decimal128 RD1r75[NRD1r75 + 1] =
{
  -2.109754689501705828789976311354395393605E8DL,
  -5.036651829232895725959911504899241062286E8DL,
  -4.954234699418689764943486770327295098084E8DL,
  -2.589558042412676610775157783898195339410E8DL,
  -7.731476117252958268044969614034776883031E7DL,
  -1.316721702252481296030801191240867486965E7DL,
  -1.201296501404876774861190604303728810836E6DL,
  -5.007966406976106636109459072523610273928E4DL,
  -6.155817990560743422008969155276229018209E2DL
  /* 1.0E0DL */
};


/* log gamma(x+x0) = y0 +  x^2 P(x)/Q(x)
   -0.0867 <= x <= +0.1634
   1.374932... <= x+x0 <= 1.625032...
   Peak relative error 4.0e-36  */
static const _Decimal128 x0a = 1.4616241455078125DL;
static const _Decimal128 x0b = 7.9994605498412626595423257213002588621246E-6DL;
static const _Decimal128 y0a = -1.21490478515625E-1DL;
static const _Decimal128 y0b = 4.1879797753919044854428223084178486438269E-6DL;
#define NRN1r5 8
static const _Decimal128 RN1r5[NRN1r5 + 1] =
{
  6.827103657233705798067415468881313128066E5DL,
  1.910041815932269464714909706705242148108E6DL,
  2.194344176925978377083808566251427771951E6DL,
  1.332921400100891472195055269688876427962E6DL,
  4.589080973377307211815655093824787123508E5DL,
  8.900334161263456942727083580232613796141E4DL,
  9.053840838306019753209127312097612455236E3DL,
  4.053367147553353374151852319743594873771E2DL,
  5.040631576303952022968949605613514584950E0DL
};
#define NRD1r5 8
static const _Decimal128 RD1r5[NRD1r5 + 1] =
{
  1.411036368843183477558773688484699813355E6DL,
  4.378121767236251950226362443134306184849E6DL,
  5.682322855631723455425929877581697918168E6DL,
  3.999065731556977782435009349967042222375E6DL,
  1.653651390456781293163585493620758410333E6DL,
  4.067774359067489605179546964969435858311E5DL,
  5.741463295366557346748361781768833633256E4DL,
  4.226404539738182992856094681115746692030E3DL,
  1.316980975410327975566999780608618774469E2DL,
  /* 1.0E0DL */
};


/* log gamma(x+1.25) = log gamma(1.25) +  x P(x)/Q(x)
   -.125 <= x <= +.125
   1.125 <= x+1.25 <= 1.375
   Peak relative error = 4.9e-36 */
static const _Decimal128 lgam1r25a = -9.82818603515625E-2DL;
static const _Decimal128 lgam1r25b = 1.0023929749338536146197303364159774377296E-5DL;
#define NRN1r25 9
static const _Decimal128 RN1r25[NRN1r25 + 1] =
{
  -9.054787275312026472896002240379580536760E4DL,
  -8.685076892989927640126560802094680794471E4DL,
  2.797898965448019916967849727279076547109E5DL,
  6.175520827134342734546868356396008898299E5DL,
  5.179626599589134831538516906517372619641E5DL,
  2.253076616239043944538380039205558242161E5DL,
  5.312653119599957228630544772499197307195E4DL,
  6.434329437514083776052669599834938898255E3DL,
  3.385414416983114598582554037612347549220E2DL,
  4.907821957946273805080625052510832015792E0DL
};
#define NRD1r25 8
static const _Decimal128 RD1r25[NRD1r25 + 1] =
{
  3.980939377333448005389084785896660309000E5DL,
  1.429634893085231519692365775184490465542E6DL,
  2.145438946455476062850151428438668234336E6DL,
  1.743786661358280837020848127465970357893E6DL,
  8.316364251289743923178092656080441655273E5DL,
  2.355732939106812496699621491135458324294E5DL,
  3.822267399625696880571810137601310855419E4DL,
  3.228463206479133236028576845538387620856E3DL,
  1.152133170470059555646301189220117965514E2DL
  /* 1.0E0DL */
};


/* log gamma(x + 1) = x P(x)/Q(x)
   0.0 <= x <= +0.125
   1.0 <= x+1 <= 1.125
   Peak relative error 1.1e-35  */
#define NRN1 8
static const _Decimal128 RN1[NRN1 + 1] =
{
  -9.987560186094800756471055681088744738818E3DL,
  -2.506039379419574361949680225279376329742E4DL,
  -1.386770737662176516403363873617457652991E4DL,
  1.439445846078103202928677244188837130744E4DL,
  2.159612048879650471489449668295139990693E4DL,
  1.047439813638144485276023138173676047079E4DL,
  2.250316398054332592560412486630769139961E3DL,
  1.958510425467720733041971651126443864041E2DL,
  4.516830313569454663374271993200291219855E0DL
};
#define NRD1 7
static const _Decimal128 RD1[NRD1 + 1] =
{
  1.730299573175751778863269333703788214547E4DL,
  6.807080914851328611903744668028014678148E4DL,
  1.090071629101496938655806063184092302439E5DL,
  9.124354356415154289343303999616003884080E4DL,
  4.262071638655772404431164427024003253954E4DL,
  1.096981664067373953673982635805821283581E4DL,
  1.431229503796575892151252708527595787588E3DL,
  7.734110684303689320830401788262295992921E1DL
 /* 1.0E0 */
};


/* log gamma(x + 1) = x P(x)/Q(x)
   -0.125 <= x <= 0
   0.875 <= x+1 <= 1.0
   Peak relative error 7.0e-37  */
#define NRNr9 8
static const _Decimal128 RNr9[NRNr9 + 1] =
{
  4.441379198241760069548832023257571176884E5DL,
  1.273072988367176540909122090089580368732E6DL,
  9.732422305818501557502584486510048387724E5DL,
  -5.040539994443998275271644292272870348684E5DL,
  -1.208719055525609446357448132109723786736E6DL,
  -7.434275365370936547146540554419058907156E5DL,
  -2.075642969983377738209203358199008185741E5DL,
  -2.565534860781128618589288075109372218042E4DL,
  -1.032901669542994124131223797515913955938E3DL,
};
#define NRDr9 8
static const _Decimal128 RDr9[NRDr9 + 1] =
{
  -7.694488331323118759486182246005193998007E5DL,
  -3.301918855321234414232308938454112213751E6DL,
  -5.856830900232338906742924836032279404702E6DL,
  -5.540672519616151584486240871424021377540E6DL,
  -3.006530901041386626148342989181721176919E6DL,
  -9.350378280513062139466966374330795935163E5DL,
  -1.566179100031063346901755685375732739511E5DL,
  -1.205016539620260779274902967231510804992E4DL,
  -2.724583156305709733221564484006088794284E2DL
/* 1.0E0 */
};


/* Evaluate P[n] x^n  +  P[n-1] x^(n-1)  +  ...  +  P[0] */

static _Decimal128
neval (_Decimal128 x, const _Decimal128 *p, int n)
{
  _Decimal128 y;

  p += n;
  y = *p--;
  do
    {
      y = y * x + *p--;
    }
  while (--n > 0);
  return y;
}


/* Evaluate x^n+1  +  P[n] x^(n)  +  P[n-1] x^(n-1)  +  ...  +  P[0] */

static _Decimal128
deval (_Decimal128 x, const _Decimal128 *p, int n)
{
  _Decimal128 y;

  p += n;
  y = x + *p--;
  do
    {
      y = y * x + *p--;
    }
  while (--n > 0);
  return y;
}

/*  The 128bit version is used by all three sizes */
/* extern _Decimal128 __lgamma_rd128 (_Decimal128, int *); */

/* extern DEC_TYPE FUNC_D (__lgamma_r) (DEC_TYPE x, int *signgamp); */

DEC_TYPE
FUNC_D (__lgamma_r) (DEC_TYPE x, int *signgamp)
{
  _Decimal128 p, q, w, z, nx;
  int i, nn;

  *signgamp = 1;

  if (isinf (x) || isnan(x))
    return x * x;

  if (x < 0.0DL)
    {
      q = -x;
      p = floord128 (q);
      /*  Argument is a negative Integer: Pole Error */
      if (p == q)
      {
        DFP_EXCEPT (FE_DIVBYZERO);
        return DFP_HUGE_VAL;
      }
      i = p;
      if ((i & 1) == 0)
      *signgamp = -1;
      z = q - p;
      if (z > 0.5DL)
      {
        p += 1.0DL;
        z = p - q;
      }
      z = q * sind128 (M_PIdl * z);
      if (z == 0.0DL)
      {
        DFP_EXCEPT (FE_OVERFLOW);
        return (DEC_TYPE)(*signgamp * huge * huge);
      }
      w = __lgamma_rd128 (q, &i);
      z = logd128 (M_PIdl / z) - w;
      return (DEC_TYPE)(z);
    }

  if (x < 13.5DL)
    {
      p = 0.0DL;
      nx =  (x + 0.5DL);
      nn = nx;
      switch (nn)
      {
      case 0:
        /* log gamma (x + 1) = log(x) + log gamma(x) */
        if (x <= 0.125DL)
          {
            p = x * neval (x, RN1, NRN1) / deval (x, RD1, NRD1);
          }
        else if (x <= 0.375DL)
          {
            z = x - 0.25DL;
            p = z * neval (z, RN1r25, NRN1r25) / deval (z, RD1r25, NRD1r25);
            p += lgam1r25b;
            p += lgam1r25a;
          }
        else if (x <= 0.625DL)
          {
            z = x + (1.0DL - x0a);
            z = z - x0b;
            p = neval (z, RN1r5, NRN1r5) / deval (z, RD1r5, NRD1r5);
            p = p * z * z;
            p = p + y0b;
            p = p + y0a;
          }
        else if (x <= 0.875DL)
          {
            z = x - 0.75DL;
            p = z * neval (z, RN1r75, NRN1r75) / deval (z, RD1r75, NRD1r75);
            p += lgam1r75b;
            p += lgam1r75a;
          }
        else
          {
            z = x - 1.0DL;
            p = z * neval (z, RN2, NRN2) / deval (z, RD2, NRD2);
          }
        p = p - FUNC_D(log) (x);
        break;

      case 1:
        if (x < 0.875DL)
          {
            if (x <= 0.625DL)
            {
              z = x + (1.0DL - x0a);
              z = z - x0b;
              p = neval (z, RN1r5, NRN1r5) / deval (z, RD1r5, NRD1r5);
              p = p * z * z;
              p = p + y0b;
              p = p + y0a;
            }
            else if (x <= 0.875DL)
            {
              z = x - 0.75DL;
              p = z * neval (z, RN1r75, NRN1r75)
                    / deval (z, RD1r75, NRD1r75);
              p += lgam1r75b;
              p += lgam1r75a;
            }
            else
            {
              z = x - 1.0DL;
              p = z * neval (z, RN2, NRN2) / deval (z, RD2, NRD2);
            }
            p = p - FUNC_D(log) (x);
          }
        else if (x < 1.0DL)
          {
            z = x - 1.0DL;
            p = z * neval (z, RNr9, NRNr9) / deval (z, RDr9, NRDr9);
          }
        else if (x == 1.0DL)
          p = 0.0DL;
        else if (x <= 1.125DL)
          {
            z = x - 1.0DL;
            p = z * neval (z, RN1, NRN1) / deval (z, RD1, NRD1);
          }
        else if (x <= 1.375DL)
          {
            z = x - 1.25DL;
            p = z * neval (z, RN1r25, NRN1r25) / deval (z, RD1r25, NRD1r25);
            p += lgam1r25b;
            p += lgam1r25a;
          }
        else
          {
            /* 1.375 <= x+x0 <= 1.625 */
            z = x - x0a;
            z = z - x0b;
            p = neval (z, RN1r5, NRN1r5) / deval (z, RD1r5, NRD1r5);
            p = p * z * z;
            p = p + y0b;
            p = p + y0a;
          }
        break;

      case 2:
        if (x < 1.625DL)
          {
            z = x - x0a;
            z = z - x0b;
            p = neval (z, RN1r5, NRN1r5) / deval (z, RD1r5, NRD1r5);
            p = p * z * z;
            p = p + y0b;
            p = p + y0a;
          }
        else if (x < 1.875DL)
          {
            z = x - 1.75DL;
            p = z * neval (z, RN1r75, NRN1r75) / deval (z, RD1r75, NRD1r75);
            p += lgam1r75b;
            p += lgam1r75a;
          }
        else if (x == 2.0DL)
          p = 0.0DL;
        else if (x < 2.375DL)
          {
            z = x - 2.0DL;
            p = z * neval (z, RN2, NRN2) / deval (z, RD2, NRD2);
          }
        else
          {
            z = x - 2.5DL;
            p = z * neval (z, RN2r5, NRN2r5) / deval (z, RD2r5, NRD2r5);
            p += lgam2r5b;
            p += lgam2r5a;
          }
        break;

      case 3:
        if (x < 2.75DL)
          {
            z = x - 2.5DL;
            p = z * neval (z, RN2r5, NRN2r5) / deval (z, RD2r5, NRD2r5);
            p += lgam2r5b;
            p += lgam2r5a;
          }
        else
          {
            z = x - 3.0DL;
            p = z * neval (z, RN3, NRN3) / deval (z, RD3, NRD3);
            p += lgam3b;
            p += lgam3a;
          }
        break;

      case 4:
        z = x - 4.0DL;
        p = z * neval (z, RN4, NRN4) / deval (z, RD4, NRD4);
        p += lgam4b;
        p += lgam4a;
        break;

      case 5:
        z = x - 5.0DL;
        p = z * neval (z, RN5, NRN5) / deval (z, RD5, NRD5);
        p += lgam5b;
        p += lgam5a;
        break;

      case 6:
        z = x - 6.0DL;
        p = z * neval (z, RN6, NRN6) / deval (z, RD6, NRD6);
        p += lgam6b;
        p += lgam6a;
        break;

      case 7:
        z = x - 7.0DL;
        p = z * neval (z, RN7, NRN7) / deval (z, RD7, NRD7);
        p += lgam7b;
        p += lgam7a;
        break;

      case 8:
        z = x - 8.0DL;
        p = z * neval (z, RN8, NRN8) / deval (z, RD8, NRD8);
        p += lgam8b;
        p += lgam8a;
        break;

      case 9:
        z = x - 9.0DL;
        p = z * neval (z, RN9, NRN9) / deval (z, RD9, NRD9);
        p += lgam9b;
        p += lgam9a;
        break;

      case 10:
        z = x - 10.0DL;
        p = z * neval (z, RN10, NRN10) / deval (z, RD10, NRD10);
        p += lgam10b;
        p += lgam10a;
        break;

      case 11:
        z = x - 11.0DL;
        p = z * neval (z, RN11, NRN11) / deval (z, RD11, NRD11);
        p += lgam11b;
        p += lgam11a;
        break;

      case 12:
        z = x - 12.0DL;
        p = z * neval (z, RN12, NRN12) / deval (z, RD12, NRD12);
        p += lgam12b;
        p += lgam12a;
        break;

      case 13:
        z = x - 13.0DL;
        p = z * neval (z, RN13, NRN13) / deval (z, RD13, NRD13);
        p += lgam13b;
        p += lgam13a;
        break;
      }
      return (DEC_TYPE) p;
    }

  if (x >= (DEC_TYPE)DEC_INFINITY)
    {
      DFP_EXCEPT (FE_OVERFLOW);
      return (DEC_TYPE)(*signgamp * huge * huge);
    }

  q = ls2pi - x;
  q = (x - 0.5DL) * FUNC_D(log) (x) + q;
  if (x <= 1.0e18DL)
    {
      p = 1.0DL / (x * x);
      q += neval (p, RASY, NRASY) / x;
    }
  return (DEC_TYPE)(q);
}

static DEC_TYPE
IEEE_FUNCTION_NAME (DEC_TYPE x) {
      int local_signgam;
      DEC_TYPE retval;
      retval = FUNC_D (__lgamma_r) (x,&local_signgam);
      return retval;
}


DEC_TYPE
INTERNAL_FUNCTION_NAME (DEC_TYPE x)
{
  DEC_TYPE z = IEEE_FUNCTION_NAME (x);
#ifndef _IEEE_LIBDFP
  if (_LIB_VERSION == _IEEE_) return z;
  /*  For this particular case, both the Pole and Overflow error make the same
   *  finite x -> infinite z result, and both generate an ERANGE errno */
  if (!FUNC_D(__isfinite) (z) && FUNC_D(__isfinite) (x))
    DFP_ERRNO (ERANGE);
#endif
  return z;
}

weak_alias (INTERNAL_FUNCTION_NAME, EXTERNAL_FUNCTION_NAME)

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