/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2007-2013 Bruce D. Evans
 * 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 unmodified, 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
 */

/**
 * Implementation of the natural logarithm of x for 128-bit format.
 *
 * First decompose x into its base 2 representation:
 *
 *    log(x) = log(X * 2**k), where X is in [1, 2)
 *           = log(X) + k * log(2).
 *
 * Let X = X_i + e, where X_i is the center of one of the intervals
 * [-1.0/256, 1.0/256), [1.0/256, 3.0/256), .... [2.0-1.0/256, 2.0+1.0/256)
 * and X is in this interval.  Then
 *
 *    log(X) = log(X_i + e)
 *           = log(X_i * (1 + e / X_i))
 *           = log(X_i) + log(1 + e / X_i).
 *
 * The values log(X_i) are tabulated below.  Let d = e / X_i and use
 *
 *    log(1 + d) = p(d)
 *
 * where p(d) = d - 0.5*d*d + ... is a special minimax polynomial of
 * suitably high degree.
 *
 * To get sufficiently small roundoff errors, k * log(2), log(X_i), and
 * sometimes (if |k| is not large) the first term in p(d) must be evaluated
 * and added up in extra precision.  Extra precision is not needed for the
 * rest of p(d).  In the worst case when k = 0 and log(X_i) is 0, the final
 * error is controlled mainly by the error in the second term in p(d).  The
 * error in this term itself is at most 0.5 ulps from the d*d operation in
 * it.  The error in this term relative to the first term is thus at most
 * 0.5 * |-0.5| * |d| < 1.0/1024 ulps.  We aim for an accumulated error of
 * at most twice this at the point of the final rounding step.  Thus the
 * final error should be at most 0.5 + 1.0/512 = 0.5020 ulps.  Exhaustive
 * testing of a float variant of this function showed a maximum final error
 * of 0.5008 ulps.  Non-exhaustive testing of a double variant of this
 * function showed a maximum final error of 0.5078 ulps (near 1+1.0/256).
 *
 * We made the maximum of |d| (and thus the total relative error and the
 * degree of p(d)) small by using a large number of intervals.  Using
 * centers of intervals instead of endpoints reduces this maximum by a
 * factor of 2 for a given number of intervals.  p(d) is special only
 * in beginning with the Taylor coefficients 0 + 1*d, which tends to happen
 * naturally.  The most accurate minimax polynomial of a given degree might
 * be different, but then we wouldn't want it since we would have to do
 * extra work to avoid roundoff error (especially for P0*d instead of d).
 */

#ifdef DEBUG
#include <assert.h>
#include <fenv.h>
#endif

#include "fpmath.h"
#include "math.h"
#ifndef NO_STRUCT_RETURN
#define STRUCT_RETURN
#endif
#include "math_private.h"

#if !defined(NO_UTAB) && !defined(NO_UTABL)
#define USE_UTAB
#endif

/*
 * Domain [-0.005280, 0.004838], range ~[-1.1577e-37, 1.1582e-37]:
 * |log(1 + d)/d - p(d)| < 2**-122.7
 */
static const long double
P2 = -0.5L,
P3 =  3.33333333333333333333333333333233795e-1L,        /*  0x15555555555555555555555554d42.0p-114L */
P4 = -2.49999999999999999999999999941139296e-1L,        /* -0x1ffffffffffffffffffffffdab14e.0p-115L */
P5 =  2.00000000000000000000000085468039943e-1L,        /*  0x19999999999999999999a6d3567f4.0p-115L */
P6 = -1.66666666666666666666696142372698408e-1L,        /* -0x15555555555555555567267a58e13.0p-115L */
P7 =  1.42857142857142857119522943477166120e-1L,        /*  0x1249249249249248ed79a0ae434de.0p-115L */
P8 = -1.24999999999999994863289015033581301e-1L;        /* -0x1fffffffffffffa13e91765e46140.0p-116L */
/* Double precision gives ~ 53 + log2(P9 * max(|d|)**8) ~= 120 bits. */
static const double
P9 =  1.1111111111111401e-1,            /*  0x1c71c71c71c7ed.0p-56 */
P10 = -1.0000000000040135e-1,           /* -0x199999999a0a92.0p-56 */
P11 =  9.0909090728136258e-2,           /*  0x1745d173962111.0p-56 */
P12 = -8.3333318851855284e-2,           /* -0x1555551722c7a3.0p-56 */
P13 =  7.6928634666404178e-2,           /*  0x13b1985204a4ae.0p-56 */
P14 = -7.1626810078462499e-2;           /* -0x12562276cdc5d0.0p-56 */

static volatile const double zero = 0;

#define INTERVALS       128
#define LOG2_INTERVALS  7
#define TSIZE           (INTERVALS + 1)
#define G(i)            (T[(i)].G)
#define F_hi(i)         (T[(i)].F_hi)
#define F_lo(i)         (T[(i)].F_lo)
#define ln2_hi          F_hi(TSIZE - 1)
#define ln2_lo          F_lo(TSIZE - 1)
#define E(i)            (U[(i)].E)
#define H(i)            (U[(i)].H)

static const struct {
        float   G;                      /* 1/(1 + i/128) rounded to 8/9 bits */
        float   F_hi;                   /* log(1 / G_i) rounded (see below) */
        /* The compiler will insert 8 bytes of padding here. */
        long double F_lo;               /* next 113 bits for log(1 / G_i) */
} T[TSIZE] = {
        /*
         * ln2_hi and each F_hi(i) are rounded to a number of bits that
         * makes F_hi(i) + dk*ln2_hi exact for all i and all dk.
         *
         * The last entry (for X just below 2) is used to define ln2_hi
         * and ln2_lo, to ensure that F_hi(i) and F_lo(i) cancel exactly
         * with dk*ln2_hi and dk*ln2_lo, respectively, when dk = -1.
         * This is needed for accuracy when x is just below 1.  (To avoid
         * special cases, such x are "reduced" strangely to X just below
         * 2 and dk = -1, and then the exact cancellation is needed
         * because any the error from any non-exactness would be too
         * large).
         *
         * The relevant range of dk is [-16445, 16383].  The maximum number
         * of bits in F_hi(i) that works is very dependent on i but has
         * a minimum of 93.  We only need about 12 bits in F_hi(i) for
         * it to provide enough extra precision.
         *
         * We round F_hi(i) to 24 bits so that it can have type float,
         * mainly to minimize the size of the table.  Using all 24 bits
         * in a float for it automatically satisfies the above constraints.
         */
     0x800000.0p-23,  0,               0,
     0xfe0000.0p-24,  0x8080ac.0p-30, -0x14ee431dae6674afa0c4bfe16e8fd.0p-144L,
     0xfc0000.0p-24,  0x8102b3.0p-29, -0x1db29ee2d83717be918e1119642ab.0p-144L,
     0xfa0000.0p-24,  0xc24929.0p-29,  0x1191957d173697cf302cc9476f561.0p-143L,
     0xf80000.0p-24,  0x820aec.0p-28,  0x13ce8888e02e78eba9b1113bc1c18.0p-142L,
     0xf60000.0p-24,  0xa33577.0p-28, -0x17a4382ce6eb7bfa509bec8da5f22.0p-142L,
     0xf48000.0p-24,  0xbc42cb.0p-28, -0x172a21161a107674986dcdca6709c.0p-143L,
     0xf30000.0p-24,  0xd57797.0p-28, -0x1e09de07cb958897a3ea46e84abb3.0p-142L,
     0xf10000.0p-24,  0xf7518e.0p-28,  0x1ae1eec1b036c484993c549c4bf40.0p-151L,
     0xef0000.0p-24,  0x8cb9df.0p-27, -0x1d7355325d560d9e9ab3d6ebab580.0p-141L,
     0xed8000.0p-24,  0x999ec0.0p-27, -0x1f9f02d256d5037108f4ec21e48cd.0p-142L,
     0xec0000.0p-24,  0xa6988b.0p-27, -0x16fc0a9d12c17a70f7a684c596b12.0p-143L,
     0xea0000.0p-24,  0xb80698.0p-27,  0x15d581c1e8da99ded322fb08b8462.0p-141L,
     0xe80000.0p-24,  0xc99af3.0p-27, -0x1535b3ba8f150ae09996d7bb4653e.0p-143L,
     0xe70000.0p-24,  0xd273b2.0p-27,  0x163786f5251aefe0ded34c8318f52.0p-145L,
     0xe50000.0p-24,  0xe442c0.0p-27,  0x1bc4b2368e32d56699c1799a244d4.0p-144L,
     0xe38000.0p-24,  0xf1b83f.0p-27,  0x1c6090f684e6766abceccab1d7174.0p-141L,
     0xe20000.0p-24,  0xff448a.0p-27, -0x1890aa69ac9f4215f93936b709efb.0p-142L,
     0xe08000.0p-24,  0x8673f6.0p-26,  0x1b9985194b6affd511b534b72a28e.0p-140L,
     0xdf0000.0p-24,  0x8d515c.0p-26, -0x1dc08d61c6ef1d9b2ef7e68680598.0p-143L,
     0xdd8000.0p-24,  0x943a9e.0p-26, -0x1f72a2dac729b3f46662238a9425a.0p-142L,
     0xdc0000.0p-24,  0x9b2fe6.0p-26, -0x1fd4dfd3a0afb9691aed4d5e3df94.0p-140L,
     0xda8000.0p-24,  0xa2315d.0p-26, -0x11b26121629c46c186384993e1c93.0p-142L,
     0xd90000.0p-24,  0xa93f2f.0p-26,  0x1286d633e8e5697dc6a402a56fce1.0p-141L,
     0xd78000.0p-24,  0xb05988.0p-26,  0x16128eba9367707ebfa540e45350c.0p-144L,
     0xd60000.0p-24,  0xb78094.0p-26,  0x16ead577390d31ef0f4c9d43f79b2.0p-140L,
     0xd50000.0p-24,  0xbc4c6c.0p-26,  0x151131ccf7c7b75e7d900b521c48d.0p-141L,
     0xd38000.0p-24,  0xc3890a.0p-26, -0x115e2cd714bd06508aeb00d2ae3e9.0p-140L,
     0xd20000.0p-24,  0xcad2d7.0p-26, -0x1847f406ebd3af80485c2f409633c.0p-142L,
     0xd10000.0p-24,  0xcfb620.0p-26,  0x1c2259904d686581799fbce0b5f19.0p-141L,
     0xcf8000.0p-24,  0xd71653.0p-26,  0x1ece57a8d5ae54f550444ecf8b995.0p-140L,
     0xce0000.0p-24,  0xde843a.0p-26, -0x1f109d4bc4595412b5d2517aaac13.0p-141L,
     0xcd0000.0p-24,  0xe37fde.0p-26,  0x1bc03dc271a74d3a85b5b43c0e727.0p-141L,
     0xcb8000.0p-24,  0xeb050c.0p-26, -0x1bf2badc0df841a71b79dd5645b46.0p-145L,
     0xca0000.0p-24,  0xf29878.0p-26, -0x18efededd89fbe0bcfbe6d6db9f66.0p-147L,
     0xc90000.0p-24,  0xf7ad6f.0p-26,  0x1373ff977baa6911c7bafcb4d84fb.0p-141L,
     0xc80000.0p-24,  0xfcc8e3.0p-26,  0x196766f2fb328337cc050c6d83b22.0p-140L,
     0xc68000.0p-24,  0x823f30.0p-25,  0x19bd076f7c434e5fcf1a212e2a91e.0p-139L,
     0xc58000.0p-24,  0x84d52c.0p-25, -0x1a327257af0f465e5ecab5f2a6f81.0p-139L,
     0xc40000.0p-24,  0x88bc74.0p-25,  0x113f23def19c5a0fe396f40f1dda9.0p-141L,
     0xc30000.0p-24,  0x8b5ae6.0p-25,  0x1759f6e6b37de945a049a962e66c6.0p-139L,
     0xc20000.0p-24,  0x8dfccb.0p-25,  0x1ad35ca6ed5147bdb6ddcaf59c425.0p-141L,
     0xc10000.0p-24,  0x90a22b.0p-25,  0x1a1d71a87deba46bae9827221dc98.0p-139L,
     0xbf8000.0p-24,  0x94a0d8.0p-25, -0x139e5210c2b730e28aba001a9b5e0.0p-140L,
     0xbe8000.0p-24,  0x974f16.0p-25, -0x18f6ebcff3ed72e23e13431adc4a5.0p-141L,
     0xbd8000.0p-24,  0x9a00f1.0p-25, -0x1aa268be39aab7148e8d80caa10b7.0p-139L,
     0xbc8000.0p-24,  0x9cb672.0p-25, -0x14c8815839c5663663d15faed7771.0p-139L,
     0xbb0000.0p-24,  0xa0cda1.0p-25,  0x1eaf46390dbb2438273918db7df5c.0p-141L,
     0xba0000.0p-24,  0xa38c6e.0p-25,  0x138e20d831f698298adddd7f32686.0p-141L,
     0xb90000.0p-24,  0xa64f05.0p-25, -0x1e8d3c41123615b147a5d47bc208f.0p-142L,
     0xb80000.0p-24,  0xa91570.0p-25,  0x1ce28f5f3840b263acb4351104631.0p-140L,
     0xb70000.0p-24,  0xabdfbb.0p-25, -0x186e5c0a42423457e22d8c650b355.0p-139L,
     0xb60000.0p-24,  0xaeadef.0p-25, -0x14d41a0b2a08a465dc513b13f567d.0p-143L,
     0xb50000.0p-24,  0xb18018.0p-25,  0x16755892770633947ffe651e7352f.0p-139L,
     0xb40000.0p-24,  0xb45642.0p-25, -0x16395ebe59b15228bfe8798d10ff0.0p-142L,
     0xb30000.0p-24,  0xb73077.0p-25,  0x1abc65c8595f088b61a335f5b688c.0p-140L,
     0xb20000.0p-24,  0xba0ec4.0p-25, -0x1273089d3dad88e7d353e9967d548.0p-139L,
     0xb10000.0p-24,  0xbcf133.0p-25,  0x10f9f67b1f4bbf45de06ecebfaf6d.0p-139L,
     0xb00000.0p-24,  0xbfd7d2.0p-25, -0x109fab904864092b34edda19a831e.0p-140L,
     0xaf0000.0p-24,  0xc2c2ac.0p-25, -0x1124680aa43333221d8a9b475a6ba.0p-139L,
     0xae8000.0p-24,  0xc439b3.0p-25, -0x1f360cc4710fbfe24b633f4e8d84d.0p-140L,
     0xad8000.0p-24,  0xc72afd.0p-25, -0x132d91f21d89c89c45003fc5d7807.0p-140L,
     0xac8000.0p-24,  0xca20a2.0p-25, -0x16bf9b4d1f8da8002f2449e174504.0p-139L,
     0xab8000.0p-24,  0xcd1aae.0p-25,  0x19deb5ce6a6a8717d5626e16acc7d.0p-141L,
     0xaa8000.0p-24,  0xd0192f.0p-25,  0x1a29fb48f7d3ca87dabf351aa41f4.0p-139L,
     0xaa0000.0p-24,  0xd19a20.0p-25,  0x1127d3c6457f9d79f51dcc73014c9.0p-141L,
     0xa90000.0p-24,  0xd49f6a.0p-25, -0x1ba930e486a0ac42d1bf9199188e7.0p-141L,
     0xa80000.0p-24,  0xd7a94b.0p-25, -0x1b6e645f31549dd1160bcc45c7e2c.0p-139L,
     0xa70000.0p-24,  0xdab7d0.0p-25,  0x1118a425494b610665377f15625b6.0p-140L,
     0xa68000.0p-24,  0xdc40d5.0p-25,  0x1966f24d29d3a2d1b2176010478be.0p-140L,
     0xa58000.0p-24,  0xdf566d.0p-25, -0x1d8e52eb2248f0c95dd83626d7333.0p-142L,
     0xa48000.0p-24,  0xe270ce.0p-25, -0x1ee370f96e6b67ccb006a5b9890ea.0p-140L,
     0xa40000.0p-24,  0xe3ffce.0p-25,  0x1d155324911f56db28da4d629d00a.0p-140L,
     0xa30000.0p-24,  0xe72179.0p-25, -0x1fe6e2f2f867d8f4d60c713346641.0p-140L,
     0xa20000.0p-24,  0xea4812.0p-25,  0x1b7be9add7f4d3b3d406b6cbf3ce5.0p-140L,
     0xa18000.0p-24,  0xebdd3d.0p-25,  0x1b3cfb3f7511dd73692609040ccc2.0p-139L,
     0xa08000.0p-24,  0xef0b5b.0p-25, -0x1220de1f7301901b8ad85c25afd09.0p-139L,
     0xa00000.0p-24,  0xf0a451.0p-25, -0x176364c9ac81cc8a4dfb804de6867.0p-140L,
     0x9f0000.0p-24,  0xf3da16.0p-25,  0x1eed6b9aafac8d42f78d3e65d3727.0p-141L,
     0x9e8000.0p-24,  0xf576e9.0p-25,  0x1d593218675af269647b783d88999.0p-139L,
     0x9d8000.0p-24,  0xf8b47c.0p-25, -0x13e8eb7da053e063714615f7cc91d.0p-144L,
     0x9d0000.0p-24,  0xfa553f.0p-25,  0x1c063259bcade02951686d5373aec.0p-139L,
     0x9c0000.0p-24,  0xfd9ac5.0p-25,  0x1ef491085fa3c1649349630531502.0p-139L,
     0x9b8000.0p-24,  0xff3f8c.0p-25,  0x1d607a7c2b8c5320619fb9433d841.0p-139L,
     0x9a8000.0p-24,  0x814697.0p-24, -0x12ad3817004f3f0bdff99f932b273.0p-138L,
     0x9a0000.0p-24,  0x821b06.0p-24, -0x189fc53117f9e54e78103a2bc1767.0p-141L,
     0x990000.0p-24,  0x83c5f8.0p-24,  0x14cf15a048907b7d7f47ddb45c5a3.0p-139L,
     0x988000.0p-24,  0x849c7d.0p-24,  0x1cbb1d35fb82873b04a9af1dd692c.0p-138L,
     0x978000.0p-24,  0x864ba6.0p-24,  0x1128639b814f9b9770d8cb6573540.0p-138L,
     0x970000.0p-24,  0x87244c.0p-24,  0x184733853300f002e836dfd47bd41.0p-139L,
     0x968000.0p-24,  0x87fdaa.0p-24,  0x109d23aef77dd5cd7cc94306fb3ff.0p-140L,
     0x958000.0p-24,  0x89b293.0p-24, -0x1a81ef367a59de2b41eeebd550702.0p-138L,
     0x950000.0p-24,  0x8a8e20.0p-24, -0x121ad3dbb2f45275c917a30df4ac9.0p-138L,
     0x948000.0p-24,  0x8b6a6a.0p-24, -0x1cfb981628af71a89df4e6df2e93b.0p-139L,
     0x938000.0p-24,  0x8d253a.0p-24, -0x1d21730ea76cfdec367828734cae5.0p-139L,
     0x930000.0p-24,  0x8e03c2.0p-24,  0x135cc00e566f76b87333891e0dec4.0p-138L,
     0x928000.0p-24,  0x8ee30d.0p-24, -0x10fcb5df257a263e3bf446c6e3f69.0p-140L,
     0x918000.0p-24,  0x90a3ee.0p-24, -0x16e171b15433d723a4c7380a448d8.0p-139L,
     0x910000.0p-24,  0x918587.0p-24, -0x1d050da07f3236f330972da2a7a87.0p-139L,
     0x908000.0p-24,  0x9267e7.0p-24,  0x1be03669a5268d21148c6002becd3.0p-139L,
     0x8f8000.0p-24,  0x942f04.0p-24,  0x10b28e0e26c336af90e00533323ba.0p-139L,
     0x8f0000.0p-24,  0x9513c3.0p-24,  0x1a1d820da57cf2f105a89060046aa.0p-138L,
     0x8e8000.0p-24,  0x95f950.0p-24, -0x19ef8f13ae3cf162409d8ea99d4c0.0p-139L,
     0x8e0000.0p-24,  0x96dfab.0p-24, -0x109e417a6e507b9dc10dac743ad7a.0p-138L,
     0x8d0000.0p-24,  0x98aed2.0p-24,  0x10d01a2c5b0e97c4990b23d9ac1f5.0p-139L,
     0x8c8000.0p-24,  0x9997a2.0p-24, -0x1d6a50d4b61ea74540bdd2aa99a42.0p-138L,
     0x8c0000.0p-24,  0x9a8145.0p-24,  0x1b3b190b83f9527e6aba8f2d783c1.0p-138L,
     0x8b8000.0p-24,  0x9b6bbf.0p-24,  0x13a69fad7e7abe7ba81c664c107e0.0p-138L,
     0x8b0000.0p-24,  0x9c5711.0p-24, -0x11cd12316f576aad348ae79867223.0p-138L,
     0x8a8000.0p-24,  0x9d433b.0p-24,  0x1c95c444b807a246726b304ccae56.0p-139L,
     0x898000.0p-24,  0x9f1e22.0p-24, -0x1b9c224ea698c2f9b47466d6123fe.0p-139L,
     0x890000.0p-24,  0xa00ce1.0p-24,  0x125ca93186cf0f38b4619a2483399.0p-141L,
     0x888000.0p-24,  0xa0fc80.0p-24, -0x1ee38a7bc228b3597043be78eaf49.0p-139L,
     0x880000.0p-24,  0xa1ed00.0p-24, -0x1a0db876613d204147dc69a07a649.0p-138L,
     0x878000.0p-24,  0xa2de62.0p-24,  0x193224e8516c008d3602a7b41c6e8.0p-139L,
     0x870000.0p-24,  0xa3d0a9.0p-24,  0x1fa28b4d2541aca7d5844606b2421.0p-139L,
     0x868000.0p-24,  0xa4c3d6.0p-24,  0x1c1b5760fb4571acbcfb03f16daf4.0p-138L,
     0x858000.0p-24,  0xa6acea.0p-24,  0x1fed5d0f65949c0a345ad743ae1ae.0p-140L,
     0x850000.0p-24,  0xa7a2d4.0p-24,  0x1ad270c9d749362382a7688479e24.0p-140L,
     0x848000.0p-24,  0xa899ab.0p-24,  0x199ff15ce532661ea9643a3a2d378.0p-139L,
     0x840000.0p-24,  0xa99171.0p-24,  0x1a19e15ccc45d257530a682b80490.0p-139L,
     0x838000.0p-24,  0xaa8a28.0p-24, -0x121a14ec532b35ba3e1f868fd0b5e.0p-140L,
     0x830000.0p-24,  0xab83d1.0p-24,  0x1aee319980bff3303dd481779df69.0p-139L,
     0x828000.0p-24,  0xac7e6f.0p-24, -0x18ffd9e3900345a85d2d86161742e.0p-140L,
     0x820000.0p-24,  0xad7a03.0p-24, -0x1e4db102ce29f79b026b64b42caa1.0p-140L,
     0x818000.0p-24,  0xae768f.0p-24,  0x17c35c55a04a82ab19f77652d977a.0p-141L,
     0x810000.0p-24,  0xaf7415.0p-24,  0x1448324047019b48d7b98c1cf7234.0p-138L,
     0x808000.0p-24,  0xb07298.0p-24, -0x1750ee3915a197e9c7359dd94152f.0p-138L,
     0x800000.0p-24,  0xb17218.0p-24, -0x105c610ca86c3898cff81a12a17e2.0p-141L,
};

#ifdef USE_UTAB
static const struct {
        float   H;                      /* 1 + i/INTERVALS (exact) */
        float   E;                      /* H(i) * G(i) - 1 (exact) */
} U[TSIZE] = {
         0x800000.0p-23,  0,
         0x810000.0p-23, -0x800000.0p-37,
         0x820000.0p-23, -0x800000.0p-35,
         0x830000.0p-23, -0x900000.0p-34,
         0x840000.0p-23, -0x800000.0p-33,
         0x850000.0p-23, -0xc80000.0p-33,
         0x860000.0p-23, -0xa00000.0p-36,
         0x870000.0p-23,  0x940000.0p-33,
         0x880000.0p-23,  0x800000.0p-35,
         0x890000.0p-23, -0xc80000.0p-34,
         0x8a0000.0p-23,  0xe00000.0p-36,
         0x8b0000.0p-23,  0x900000.0p-33,
         0x8c0000.0p-23, -0x800000.0p-35,
         0x8d0000.0p-23, -0xe00000.0p-33,
         0x8e0000.0p-23,  0x880000.0p-33,
         0x8f0000.0p-23, -0xa80000.0p-34,
         0x900000.0p-23, -0x800000.0p-35,
         0x910000.0p-23,  0x800000.0p-37,
         0x920000.0p-23,  0x900000.0p-35,
         0x930000.0p-23,  0xd00000.0p-35,
         0x940000.0p-23,  0xe00000.0p-35,
         0x950000.0p-23,  0xc00000.0p-35,
         0x960000.0p-23,  0xe00000.0p-36,
         0x970000.0p-23, -0x800000.0p-38,
         0x980000.0p-23, -0xc00000.0p-35,
         0x990000.0p-23, -0xd00000.0p-34,
         0x9a0000.0p-23,  0x880000.0p-33,
         0x9b0000.0p-23,  0xe80000.0p-35,
         0x9c0000.0p-23, -0x800000.0p-35,
         0x9d0000.0p-23,  0xb40000.0p-33,
         0x9e0000.0p-23,  0x880000.0p-34,
         0x9f0000.0p-23, -0xe00000.0p-35,
         0xa00000.0p-23,  0x800000.0p-33,
         0xa10000.0p-23, -0x900000.0p-36,
         0xa20000.0p-23, -0xb00000.0p-33,
         0xa30000.0p-23, -0xa00000.0p-36,
         0xa40000.0p-23,  0x800000.0p-33,
         0xa50000.0p-23, -0xf80000.0p-35,
         0xa60000.0p-23,  0x880000.0p-34,
         0xa70000.0p-23, -0x900000.0p-33,
         0xa80000.0p-23, -0x800000.0p-35,
         0xa90000.0p-23,  0x900000.0p-34,
         0xaa0000.0p-23,  0xa80000.0p-33,
         0xab0000.0p-23, -0xac0000.0p-34,
         0xac0000.0p-23, -0x800000.0p-37,
         0xad0000.0p-23,  0xf80000.0p-35,
         0xae0000.0p-23,  0xf80000.0p-34,
         0xaf0000.0p-23, -0xac0000.0p-33,
         0xb00000.0p-23, -0x800000.0p-33,
         0xb10000.0p-23, -0xb80000.0p-34,
         0xb20000.0p-23, -0x800000.0p-34,
         0xb30000.0p-23, -0xb00000.0p-35,
         0xb40000.0p-23, -0x800000.0p-35,
         0xb50000.0p-23, -0xe00000.0p-36,
         0xb60000.0p-23, -0x800000.0p-35,
         0xb70000.0p-23, -0xb00000.0p-35,
         0xb80000.0p-23, -0x800000.0p-34,
         0xb90000.0p-23, -0xb80000.0p-34,
         0xba0000.0p-23, -0x800000.0p-33,
         0xbb0000.0p-23, -0xac0000.0p-33,
         0xbc0000.0p-23,  0x980000.0p-33,
         0xbd0000.0p-23,  0xbc0000.0p-34,
         0xbe0000.0p-23,  0xe00000.0p-36,
         0xbf0000.0p-23, -0xb80000.0p-35,
         0xc00000.0p-23, -0x800000.0p-33,
         0xc10000.0p-23,  0xa80000.0p-33,
         0xc20000.0p-23,  0x900000.0p-34,
         0xc30000.0p-23, -0x800000.0p-35,
         0xc40000.0p-23, -0x900000.0p-33,
         0xc50000.0p-23,  0x820000.0p-33,
         0xc60000.0p-23,  0x800000.0p-38,
         0xc70000.0p-23, -0x820000.0p-33,
         0xc80000.0p-23,  0x800000.0p-33,
         0xc90000.0p-23, -0xa00000.0p-36,
         0xca0000.0p-23, -0xb00000.0p-33,
         0xcb0000.0p-23,  0x840000.0p-34,
         0xcc0000.0p-23, -0xd00000.0p-34,
         0xcd0000.0p-23,  0x800000.0p-33,
         0xce0000.0p-23, -0xe00000.0p-35,
         0xcf0000.0p-23,  0xa60000.0p-33,
         0xd00000.0p-23, -0x800000.0p-35,
         0xd10000.0p-23,  0xb40000.0p-33,
         0xd20000.0p-23, -0x800000.0p-35,
         0xd30000.0p-23,  0xaa0000.0p-33,
         0xd40000.0p-23, -0xe00000.0p-35,
         0xd50000.0p-23,  0x880000.0p-33,
         0xd60000.0p-23, -0xd00000.0p-34,
         0xd70000.0p-23,  0x9c0000.0p-34,
         0xd80000.0p-23, -0xb00000.0p-33,
         0xd90000.0p-23, -0x800000.0p-38,
         0xda0000.0p-23,  0xa40000.0p-33,
         0xdb0000.0p-23, -0xdc0000.0p-34,
         0xdc0000.0p-23,  0xc00000.0p-35,
         0xdd0000.0p-23,  0xca0000.0p-33,
         0xde0000.0p-23, -0xb80000.0p-34,
         0xdf0000.0p-23,  0xd00000.0p-35,
         0xe00000.0p-23,  0xc00000.0p-33,
         0xe10000.0p-23, -0xf40000.0p-34,
         0xe20000.0p-23,  0x800000.0p-37,
         0xe30000.0p-23,  0x860000.0p-33,
         0xe40000.0p-23, -0xc80000.0p-33,
         0xe50000.0p-23, -0xa80000.0p-34,
         0xe60000.0p-23,  0xe00000.0p-36,
         0xe70000.0p-23,  0x880000.0p-33,
         0xe80000.0p-23, -0xe00000.0p-33,
         0xe90000.0p-23, -0xfc0000.0p-34,
         0xea0000.0p-23, -0x800000.0p-35,
         0xeb0000.0p-23,  0xe80000.0p-35,
         0xec0000.0p-23,  0x900000.0p-33,
         0xed0000.0p-23,  0xe20000.0p-33,
         0xee0000.0p-23, -0xac0000.0p-33,
         0xef0000.0p-23, -0xc80000.0p-34,
         0xf00000.0p-23, -0x800000.0p-35,
         0xf10000.0p-23,  0x800000.0p-35,
         0xf20000.0p-23,  0xb80000.0p-34,
         0xf30000.0p-23,  0x940000.0p-33,
         0xf40000.0p-23,  0xc80000.0p-33,
         0xf50000.0p-23, -0xf20000.0p-33,
         0xf60000.0p-23, -0xc80000.0p-33,
         0xf70000.0p-23, -0xa20000.0p-33,
         0xf80000.0p-23, -0x800000.0p-33,
         0xf90000.0p-23, -0xc40000.0p-34,
         0xfa0000.0p-23, -0x900000.0p-34,
         0xfb0000.0p-23, -0xc80000.0p-35,
         0xfc0000.0p-23, -0x800000.0p-35,
         0xfd0000.0p-23, -0x900000.0p-36,
         0xfe0000.0p-23, -0x800000.0p-37,
         0xff0000.0p-23, -0x800000.0p-39,
         0x800000.0p-22,  0,
};
#endif /* USE_UTAB */

#ifdef STRUCT_RETURN
#define RETURN1(rp, v) do {     \
        (rp)->hi = (v);         \
        (rp)->lo_set = 0;       \
        return;                 \
} while (0)

#define RETURN2(rp, h, l) do {  \
        (rp)->hi = (h);         \
        (rp)->lo = (l);         \
        (rp)->lo_set = 1;       \
        return;                 \
} while (0)

struct ld {
        long double hi;
        long double lo;
        int     lo_set;
};
#else
#define RETURN1(rp, v)  RETURNF(v)
#define RETURN2(rp, h, l)       RETURNI((h) + (l))
#endif

#ifdef STRUCT_RETURN
static __always_inline void
k_logl(long double x, struct ld *rp)
#else
long double
logl(long double x)
#endif
{
        long double d, val_hi, val_lo;
        double dd, dk;
        uint64_t lx, llx;
        int i, k;
        uint16_t hx;

        EXTRACT_LDBL128_WORDS(hx, lx, llx, x);
        k = -16383;
#if 0 /* Hard to do efficiently.  Don't do it until we support all modes. */
        if (x == 1)
                RETURN1(rp, 0);         /* log(1) = +0 in all rounding modes */
#endif
        if (hx == 0 || hx >= 0x8000) {  /* zero, negative or subnormal? */
                if (((hx & 0x7fff) | lx | llx) == 0)
                        RETURN1(rp, -1 / zero); /* log(+-0) = -Inf */
                if (hx != 0)
                        /* log(neg or NaN) = qNaN: */
                        RETURN1(rp, (x - x) / zero);
                x *= 0x1.0p113;         /* subnormal; scale up x */
                EXTRACT_LDBL128_WORDS(hx, lx, llx, x);
                k = -16383 - 113;
        } else if (hx >= 0x7fff)
                RETURN1(rp, x + x);     /* log(Inf or NaN) = Inf or qNaN */
#ifndef STRUCT_RETURN
        ENTERI();
#endif
        k += hx;
        dk = k;

        /* Scale x to be in [1, 2). */
        SET_LDBL_EXPSIGN(x, 0x3fff);

        /* 0 <= i <= INTERVALS: */
#define L2I     (49 - LOG2_INTERVALS)
        i = (lx + (1LL << (L2I - 2))) >> (L2I - 1);

        /*
         * -0.005280 < d < 0.004838.  In particular, the infinite-
         * precision |d| is <= 2**-7.  Rounding of G(i) to 8 bits
         * ensures that d is representable without extra precision for
         * this bound on |d| (since when this calculation is expressed
         * as x*G(i)-1, the multiplication needs as many extra bits as
         * G(i) has and the subtraction cancels 8 bits).  But for
         * most i (107 cases out of 129), the infinite-precision |d|
         * is <= 2**-8.  G(i) is rounded to 9 bits for such i to give
         * better accuracy (this works by improving the bound on |d|,
         * which in turn allows rounding to 9 bits in more cases).
         * This is only important when the original x is near 1 -- it
         * lets us avoid using a special method to give the desired
         * accuracy for such x.
         */
        if (0)
                d = x * G(i) - 1;
        else {
#ifdef USE_UTAB
                d = (x - H(i)) * G(i) + E(i);
#else
                long double x_hi;
                double x_lo;

                /*
                 * Split x into x_hi + x_lo to calculate x*G(i)-1 exactly.
                 * G(i) has at most 9 bits, so the splitting point is not
                 * critical.
                 */
                INSERT_LDBL128_WORDS(x_hi, 0x3fff, lx,
                    llx & 0xffffffffff000000ULL);
                x_lo = x - x_hi;
                d = x_hi * G(i) - 1 + x_lo * G(i);
#endif
        }

        /*
         * Our algorithm depends on exact cancellation of F_lo(i) and
         * F_hi(i) with dk*ln_2_lo and dk*ln2_hi when k is -1 and i is
         * at the end of the table.  This and other technical complications
         * make it difficult to avoid the double scaling in (dk*ln2) *
         * log(base) for base != e without losing more accuracy and/or
         * efficiency than is gained.
         */
        /*
         * Use double precision operations wherever possible, since
         * long double operations are emulated and were very slow on
         * the old sparc64 and unknown on the newer aarch64 and riscv
         * machines.  Also, don't try to improve parallelism by
         * increasing the number of operations, since any parallelism
         * on such machines is needed for the emulation.  Horner's
         * method is good for this, and is also good for accuracy.
         * Horner's method doesn't handle the `lo' term well, either
         * for efficiency or accuracy.  However, for accuracy we
         * evaluate d * d * P2 separately to take advantage of by P2
         * being exact, and this gives a good place to sum the 'lo'
         * term too.
         */
        dd = (double)d;
        val_lo = d * d * d * (P3 +
            d * (P4 + d * (P5 + d * (P6 + d * (P7 + d * (P8 +
            dd * (P9 + dd * (P10 + dd * (P11 + dd * (P12 + dd * (P13 +
            dd * P14))))))))))) + (F_lo(i) + dk * ln2_lo) + d * d * P2;
        val_hi = d;
#ifdef DEBUG
        if (fetestexcept(FE_UNDERFLOW))
                breakpoint();
#endif

        _3sumF(val_hi, val_lo, F_hi(i) + dk * ln2_hi);
        RETURN2(rp, val_hi, val_lo);
}

long double
log1pl(long double x)
{
        long double d, d_hi, f_lo, val_hi, val_lo;
        long double f_hi, twopminusk;
        double d_lo, dd, dk;
        uint64_t lx, llx;
        int i, k;
        int16_t ax, hx;

        EXTRACT_LDBL128_WORDS(hx, lx, llx, x);
        if (hx < 0x3fff) {              /* x < 1, or x neg NaN */
                ax = hx & 0x7fff;
                if (ax >= 0x3fff) {     /* x <= -1, or x neg NaN */
                        if (ax == 0x3fff && (lx | llx) == 0)
                                RETURNF(-1 / zero);     /* log1p(-1) = -Inf */
                        /* log1p(x < 1, or x NaN) = qNaN: */
                        RETURNF((x - x) / (x - x));
                }
                if (ax <= 0x3f8d) {     /* |x| < 2**-113 */
                        if ((int)x == 0)
                                RETURNF(x);     /* x with inexact if x != 0 */
                }
                f_hi = 1;
                f_lo = x;
        } else if (hx >= 0x7fff) {      /* x +Inf or non-neg NaN */
                RETURNF(x + x);         /* log1p(Inf or NaN) = Inf or qNaN */
        } else if (hx < 0x40e1) {       /* 1 <= x < 2**226 */
                f_hi = x;
                f_lo = 1;
        } else {                        /* 2**226 <= x < +Inf */
                f_hi = x;
                f_lo = 0;               /* avoid underflow of the P3 term */
        }
        ENTERI();
        x = f_hi + f_lo;
        f_lo = (f_hi - x) + f_lo;

        EXTRACT_LDBL128_WORDS(hx, lx, llx, x);
        k = -16383;

        k += hx;
        dk = k;

        SET_LDBL_EXPSIGN(x, 0x3fff);
        twopminusk = 1;
        SET_LDBL_EXPSIGN(twopminusk, 0x7ffe - (hx & 0x7fff));
        f_lo *= twopminusk;

        i = (lx + (1LL << (L2I - 2))) >> (L2I - 1);

        /*
         * x*G(i)-1 (with a reduced x) can be represented exactly, as
         * above, but now we need to evaluate the polynomial on d =
         * (x+f_lo)*G(i)-1 and extra precision is needed for that.
         * Since x+x_lo is a hi+lo decomposition and subtracting 1
         * doesn't lose too many bits, an inexact calculation for
         * f_lo*G(i) is good enough.
         */
        if (0)
                d_hi = x * G(i) - 1;
        else {
#ifdef USE_UTAB
                d_hi = (x - H(i)) * G(i) + E(i);
#else
                long double x_hi;
                double x_lo;

                INSERT_LDBL128_WORDS(x_hi, 0x3fff, lx,
                    llx & 0xffffffffff000000ULL);
                x_lo = x - x_hi;
                d_hi = x_hi * G(i) - 1 + x_lo * G(i);
#endif
        }
        d_lo = f_lo * G(i);

        /*
         * This is _2sumF(d_hi, d_lo) inlined.  The condition
         * (d_hi == 0 || |d_hi| >= |d_lo|) for using _2sumF() is not
         * always satisifed, so it is not clear that this works, but
         * it works in practice.  It works even if it gives a wrong
         * normalized d_lo, since |d_lo| > |d_hi| implies that i is
         * nonzero and d is tiny, so the F(i) term dominates d_lo.
         * In float precision:
         * (By exhaustive testing, the worst case is d_hi = 0x1.bp-25.
         * And if d is only a little tinier than that, we would have
         * another underflow problem for the P3 term; this is also ruled
         * out by exhaustive testing.)
         */
        d = d_hi + d_lo;
        d_lo = d_hi - d + d_lo;
        d_hi = d;

        dd = (double)d;
        val_lo = d * d * d * (P3 +
            d * (P4 + d * (P5 + d * (P6 + d * (P7 + d * (P8 +
            dd * (P9 + dd * (P10 + dd * (P11 + dd * (P12 + dd * (P13 +
            dd * P14))))))))))) + (F_lo(i) + dk * ln2_lo + d_lo) + d * d * P2;
        val_hi = d_hi;
#ifdef DEBUG
        if (fetestexcept(FE_UNDERFLOW))
                breakpoint();
#endif

        _3sumF(val_hi, val_lo, F_hi(i) + dk * ln2_hi);
        RETURNI(val_hi + val_lo);
}

#ifdef STRUCT_RETURN

long double
logl(long double x)
{
        struct ld r;

        ENTERI();
        k_logl(x, &r);
        RETURNSPI(&r);
}

/*
 * 29+113 bit decompositions.  The bits are distributed so that the products
 * of the hi terms are exact in double precision.  The types are chosen so
 * that the products of the hi terms are done in at least double precision,
 * without any explicit conversions.  More natural choices would require a
 * slow long double precision multiplication.
 */
static const double
invln10_hi =  4.3429448176175356e-1,            /*  0x1bcb7b15000000.0p-54 */
invln2_hi =  1.4426950402557850e0;              /*  0x17154765000000.0p-52 */
static const long double
invln10_lo =  1.41498268538580090791605082294397000e-10L,       /*  0x137287195355baaafad33dc323ee3.0p-145L */
invln2_lo =  6.33178418956604368501892137426645911e-10L,        /*  0x15c17f0bbbe87fed0691d3e88eb57.0p-143L */
invln10_lo_plus_hi = invln10_lo + invln10_hi,
invln2_lo_plus_hi = invln2_lo + invln2_hi;

long double
log10l(long double x)
{
        struct ld r;
        long double hi, lo;

        ENTERI();
        k_logl(x, &r);
        if (!r.lo_set)
                RETURNI(r.hi);
        _2sumF(r.hi, r.lo);
        hi = (float)r.hi;
        lo = r.lo + (r.hi - hi);
        RETURNI(invln10_hi * hi + (invln10_lo_plus_hi * lo + invln10_lo * hi));
}

long double
log2l(long double x)
{
        struct ld r;
        long double hi, lo;

        ENTERI();
        k_logl(x, &r);
        if (!r.lo_set)
                RETURNI(r.hi);
        _2sumF(r.hi, r.lo);
        hi = (float)r.hi;
        lo = r.lo + (r.hi - hi);
        RETURNI(invln2_hi * hi + (invln2_lo_plus_hi * lo + invln2_lo * hi));
}

#endif /* STRUCT_RETURN */