| /*- |
| * SPDX-License-Identifier: BSD-3-Clause |
| * |
| * Copyright (c) 1992, 1993 |
| * The Regents of the University of California. All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * 1. Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * 2. Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * 3. Neither the name of the University nor the names of its contributors |
| * may be used to endorse or promote products derived from this software |
| * without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND |
| * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE |
| * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
| * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS |
| * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
| * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY |
| * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| * SUCH DAMAGE. |
| */ |
| |
| /* Table-driven natural logarithm. |
| * |
| * This code was derived, with minor modifications, from: |
| * Peter Tang, "Table-Driven Implementation of the |
| * Logarithm in IEEE Floating-Point arithmetic." ACM Trans. |
| * Math Software, vol 16. no 4, pp 378-400, Dec 1990). |
| * |
| * Calculates log(2^m*F*(1+f/F)), |f/F| <= 1/256, |
| * where F = j/128 for j an integer in [0, 128]. |
| * |
| * log(2^m) = log2_hi*m + log2_tail*m |
| * The leading term is exact, because m is an integer, |
| * m has at most 10 digits (for subnormal numbers), |
| * and log2_hi has 11 trailing zero bits. |
| * |
| * log(F) = logF_hi[j] + logF_lo[j] is in table below. |
| * logF_hi[] + 512 is exact. |
| * |
| * log(1+f/F) = 2*f/(2*F + f) + 1/12 * (2*f/(2*F + f))**3 + ... |
| * |
| * The leading term is calculated to extra precision in two |
| * parts, the larger of which adds exactly to the dominant |
| * m and F terms. |
| * |
| * There are two cases: |
| * 1. When m and j are non-zero (m | j), use absolute |
| * precision for the leading term. |
| * 2. When m = j = 0, |1-x| < 1/256, and log(x) ~= (x-1). |
| * In this case, use a relative precision of 24 bits. |
| * (This is done differently in the original paper) |
| * |
| * Special cases: |
| * 0 return signalling -Inf |
| * neg return signalling NaN |
| * +Inf return +Inf |
| */ |
| |
| #define N 128 |
| |
| /* |
| * Coefficients in the polynomial approximation of log(1+f/F). |
| * Domain of x is [0,1./256] with 2**(-64.187) precision. |
| */ |
| static const double |
| A1 = 8.3333333333333329e-02, /* 0x3fb55555, 0x55555555 */ |
| A2 = 1.2499999999943598e-02, /* 0x3f899999, 0x99991a98 */ |
| A3 = 2.2321527525957776e-03; /* 0x3f624929, 0xe24e70be */ |
| |
| /* |
| * Table of log(Fj) = logF_head[j] + logF_tail[j], for Fj = 1+j/128. |
| * Used for generation of extend precision logarithms. |
| * The constant 35184372088832 is 2^45, so the divide is exact. |
| * It ensures correct reading of logF_head, even for inaccurate |
| * decimal-to-binary conversion routines. (Everybody gets the |
| * right answer for integers less than 2^53.) |
| * Values for log(F) were generated using error < 10^-57 absolute |
| * with the bc -l package. |
| */ |
| static double logF_head[N+1] = { |
| 0., |
| .007782140442060381246, |
| .015504186535963526694, |
| .023167059281547608406, |
| .030771658666765233647, |
| .038318864302141264488, |
| .045809536031242714670, |
| .053244514518837604555, |
| .060624621816486978786, |
| .067950661908525944454, |
| .075223421237524235039, |
| .082443669210988446138, |
| .089612158689760690322, |
| .096729626458454731618, |
| .103796793681567578460, |
| .110814366340264314203, |
| .117783035656430001836, |
| .124703478501032805070, |
| .131576357788617315236, |
| .138402322859292326029, |
| .145182009844575077295, |
| .151916042025732167530, |
| .158605030176659056451, |
| .165249572895390883786, |
| .171850256926518341060, |
| .178407657472689606947, |
| .184922338493834104156, |
| .191394852999565046047, |
| .197825743329758552135, |
| .204215541428766300668, |
| .210564769107350002741, |
| .216873938300523150246, |
| .223143551314024080056, |
| .229374101064877322642, |
| .235566071312860003672, |
| .241719936886966024758, |
| .247836163904594286577, |
| .253915209980732470285, |
| .259957524436686071567, |
| .265963548496984003577, |
| .271933715484010463114, |
| .277868451003087102435, |
| .283768173130738432519, |
| .289633292582948342896, |
| .295464212893421063199, |
| .301261330578199704177, |
| .307025035294827830512, |
| .312755710004239517729, |
| .318453731118097493890, |
| .324119468654316733591, |
| .329753286372579168528, |
| .335355541920762334484, |
| .340926586970454081892, |
| .346466767346100823488, |
| .351976423156884266063, |
| .357455888922231679316, |
| .362905493689140712376, |
| .368325561158599157352, |
| .373716409793814818840, |
| .379078352934811846353, |
| .384411698910298582632, |
| .389716751140440464951, |
| .394993808240542421117, |
| .400243164127459749579, |
| .405465108107819105498, |
| .410659924985338875558, |
| .415827895143593195825, |
| .420969294644237379543, |
| .426084395310681429691, |
| .431173464818130014464, |
| .436236766774527495726, |
| .441274560805140936281, |
| .446287102628048160113, |
| .451274644139630254358, |
| .456237433481874177232, |
| .461175715122408291790, |
| .466089729924533457960, |
| .470979715219073113985, |
| .475845904869856894947, |
| .480688529345570714212, |
| .485507815781602403149, |
| .490303988045525329653, |
| .495077266798034543171, |
| .499827869556611403822, |
| .504556010751912253908, |
| .509261901790523552335, |
| .513945751101346104405, |
| .518607764208354637958, |
| .523248143765158602036, |
| .527867089620485785417, |
| .532464798869114019908, |
| .537041465897345915436, |
| .541597282432121573947, |
| .546132437597407260909, |
| .550647117952394182793, |
| .555141507540611200965, |
| .559615787935399566777, |
| .564070138285387656651, |
| .568504735352689749561, |
| .572919753562018740922, |
| .577315365035246941260, |
| .581691739635061821900, |
| .586049045003164792433, |
| .590387446602107957005, |
| .594707107746216934174, |
| .599008189645246602594, |
| .603290851438941899687, |
| .607555250224322662688, |
| .611801541106615331955, |
| .616029877215623855590, |
| .620240409751204424537, |
| .624433288012369303032, |
| .628608659422752680256, |
| .632766669570628437213, |
| .636907462236194987781, |
| .641031179420679109171, |
| .645137961373620782978, |
| .649227946625615004450, |
| .653301272011958644725, |
| .657358072709030238911, |
| .661398482245203922502, |
| .665422632544505177065, |
| .669430653942981734871, |
| .673422675212350441142, |
| .677398823590920073911, |
| .681359224807238206267, |
| .685304003098281100392, |
| .689233281238557538017, |
| .693147180560117703862 |
| }; |
| |
| static double logF_tail[N+1] = { |
| 0., |
| -.00000000000000543229938420049, |
| .00000000000000172745674997061, |
| -.00000000000001323017818229233, |
| -.00000000000001154527628289872, |
| -.00000000000000466529469958300, |
| .00000000000005148849572685810, |
| -.00000000000002532168943117445, |
| -.00000000000005213620639136504, |
| -.00000000000001819506003016881, |
| .00000000000006329065958724544, |
| .00000000000008614512936087814, |
| -.00000000000007355770219435028, |
| .00000000000009638067658552277, |
| .00000000000007598636597194141, |
| .00000000000002579999128306990, |
| -.00000000000004654729747598444, |
| -.00000000000007556920687451336, |
| .00000000000010195735223708472, |
| -.00000000000017319034406422306, |
| -.00000000000007718001336828098, |
| .00000000000010980754099855238, |
| -.00000000000002047235780046195, |
| -.00000000000008372091099235912, |
| .00000000000014088127937111135, |
| .00000000000012869017157588257, |
| .00000000000017788850778198106, |
| .00000000000006440856150696891, |
| .00000000000016132822667240822, |
| -.00000000000007540916511956188, |
| -.00000000000000036507188831790, |
| .00000000000009120937249914984, |
| .00000000000018567570959796010, |
| -.00000000000003149265065191483, |
| -.00000000000009309459495196889, |
| .00000000000017914338601329117, |
| -.00000000000001302979717330866, |
| .00000000000023097385217586939, |
| .00000000000023999540484211737, |
| .00000000000015393776174455408, |
| -.00000000000036870428315837678, |
| .00000000000036920375082080089, |
| -.00000000000009383417223663699, |
| .00000000000009433398189512690, |
| .00000000000041481318704258568, |
| -.00000000000003792316480209314, |
| .00000000000008403156304792424, |
| -.00000000000034262934348285429, |
| .00000000000043712191957429145, |
| -.00000000000010475750058776541, |
| -.00000000000011118671389559323, |
| .00000000000037549577257259853, |
| .00000000000013912841212197565, |
| .00000000000010775743037572640, |
| .00000000000029391859187648000, |
| -.00000000000042790509060060774, |
| .00000000000022774076114039555, |
| .00000000000010849569622967912, |
| -.00000000000023073801945705758, |
| .00000000000015761203773969435, |
| .00000000000003345710269544082, |
| -.00000000000041525158063436123, |
| .00000000000032655698896907146, |
| -.00000000000044704265010452446, |
| .00000000000034527647952039772, |
| -.00000000000007048962392109746, |
| .00000000000011776978751369214, |
| -.00000000000010774341461609578, |
| .00000000000021863343293215910, |
| .00000000000024132639491333131, |
| .00000000000039057462209830700, |
| -.00000000000026570679203560751, |
| .00000000000037135141919592021, |
| -.00000000000017166921336082431, |
| -.00000000000028658285157914353, |
| -.00000000000023812542263446809, |
| .00000000000006576659768580062, |
| -.00000000000028210143846181267, |
| .00000000000010701931762114254, |
| .00000000000018119346366441110, |
| .00000000000009840465278232627, |
| -.00000000000033149150282752542, |
| -.00000000000018302857356041668, |
| -.00000000000016207400156744949, |
| .00000000000048303314949553201, |
| -.00000000000071560553172382115, |
| .00000000000088821239518571855, |
| -.00000000000030900580513238244, |
| -.00000000000061076551972851496, |
| .00000000000035659969663347830, |
| .00000000000035782396591276383, |
| -.00000000000046226087001544578, |
| .00000000000062279762917225156, |
| .00000000000072838947272065741, |
| .00000000000026809646615211673, |
| -.00000000000010960825046059278, |
| .00000000000002311949383800537, |
| -.00000000000058469058005299247, |
| -.00000000000002103748251144494, |
| -.00000000000023323182945587408, |
| -.00000000000042333694288141916, |
| -.00000000000043933937969737844, |
| .00000000000041341647073835565, |
| .00000000000006841763641591466, |
| .00000000000047585534004430641, |
| .00000000000083679678674757695, |
| -.00000000000085763734646658640, |
| .00000000000021913281229340092, |
| -.00000000000062242842536431148, |
| -.00000000000010983594325438430, |
| .00000000000065310431377633651, |
| -.00000000000047580199021710769, |
| -.00000000000037854251265457040, |
| .00000000000040939233218678664, |
| .00000000000087424383914858291, |
| .00000000000025218188456842882, |
| -.00000000000003608131360422557, |
| -.00000000000050518555924280902, |
| .00000000000078699403323355317, |
| -.00000000000067020876961949060, |
| .00000000000016108575753932458, |
| .00000000000058527188436251509, |
| -.00000000000035246757297904791, |
| -.00000000000018372084495629058, |
| .00000000000088606689813494916, |
| .00000000000066486268071468700, |
| .00000000000063831615170646519, |
| .00000000000025144230728376072, |
| -.00000000000017239444525614834 |
| }; |
| /* |
| * Extra precision variant, returning struct {double a, b;}; |
| * log(x) = a+b to 63 bits, with 'a' rounded to 24 bits. |
| */ |
| static struct Double |
| __log__D(double x) |
| { |
| int m, j; |
| double F, f, g, q, u, v, u1, u2; |
| struct Double r; |
| |
| /* |
| * Argument reduction: 1 <= g < 2; x/2^m = g; |
| * y = F*(1 + f/F) for |f| <= 2^-8 |
| */ |
| g = frexp(x, &m); |
| g *= 2; |
| m--; |
| if (m == -1022) { |
| j = ilogb(g); |
| m += j; |
| g = ldexp(g, -j); |
| } |
| j = N * (g - 1) + 0.5; |
| F = (1. / N) * j + 1; |
| f = g - F; |
| |
| g = 1 / (2 * F + f); |
| u = 2 * f * g; |
| v = u * u; |
| q = u * v * (A1 + v * (A2 + v * A3)); |
| if (m | j) { |
| u1 = u + 513; |
| u1 -= 513; |
| } else { |
| u1 = (float)u; |
| } |
| u2 = (2 * (f - F * u1) - u1 * f) * g; |
| |
| u1 += m * logF_head[N] + logF_head[j]; |
| |
| u2 += logF_tail[j]; |
| u2 += q; |
| u2 += logF_tail[N] * m; |
| r.a = (float)(u1 + u2); /* Only difference is here. */ |
| r.b = (u1 - r.a) + u2; |
| return (r); |
| } |