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Diffstat (limited to 'sysdeps/generic/log.c')
| -rw-r--r-- | sysdeps/generic/log.c | 486 |
1 files changed, 486 insertions, 0 deletions
diff --git a/sysdeps/generic/log.c b/sysdeps/generic/log.c new file mode 100644 index 0000000000..ae186722f8 --- /dev/null +++ b/sysdeps/generic/log.c @@ -0,0 +1,486 @@ +/* + * 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. All advertising materials mentioning features or use of this software + * must display the following acknowledgement: + * This product includes software developed by the University of + * California, Berkeley and its contributors. + * 4. Neither the name of the University nor the names of its contributors + * may be used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + */ + +#ifndef lint +static char sccsid[] = "@(#)log.c 8.2 (Berkeley) 11/30/93"; +#endif /* not lint */ + +#include <math.h> +#include <errno.h> + +#include "mathimpl.h" + +/* 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/j| <= 1/256, + * where F = j/128 for j an integer in [0, 128]. + * + * log(2^m) = log2_hi*m + log2_tail*m + * since m is an integer, the dominant term is exact. + * 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 tabular form in log_table.h + * 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, 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 +*/ + +#if defined(vax) || defined(tahoe) +#define _IEEE 0 +#define TRUNC(x) x = (double) (float) (x) +#else +#define _IEEE 1 +#define endian (((*(int *) &one)) ? 1 : 0) +#define TRUNC(x) *(((int *) &x) + endian) &= 0xf8000000 +#define infnan(x) 0.0 +#endif + +#define N 128 + +/* 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 A1 = .08333333333333178827; +static double A2 = .01250000000377174923; +static double A3 = .002232139987919447809; +static double A4 = .0004348877777076145742; + +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 +}; + +double +#ifdef _ANSI_SOURCE +log(double x) +#else +log(x) double x; +#endif +{ + int m, j; + double F, f, g, q, u, u2, v, zero = 0.0, one = 1.0; + volatile double u1; + + /* Catch special cases */ + if (x <= 0) + if (_IEEE && x == zero) /* log(0) = -Inf */ + return (-one/zero); + else if (_IEEE) /* log(neg) = NaN */ + return (zero/zero); + else if (x == zero) /* NOT REACHED IF _IEEE */ + return (infnan(-ERANGE)); + else + return (infnan(EDOM)); + else if (!finite(x)) + if (_IEEE) /* x = NaN, Inf */ + return (x+x); + else + return (infnan(ERANGE)); + + /* Argument reduction: 1 <= g < 2; x/2^m = g; */ + /* y = F*(1 + f/F) for |f| <= 2^-8 */ + + m = logb(x); + g = ldexp(x, -m); + if (_IEEE && m == -1022) { + j = logb(g), m += j; + g = ldexp(g, -j); + } + j = N*(g-1) + .5; + F = (1.0/N) * j + 1; /* F*128 is an integer in [128, 512] */ + f = g - F; + + /* Approximate expansion for log(1+f/F) ~= u + q */ + g = 1/(2*F+f); + u = 2*f*g; + v = u*u; + q = u*v*(A1 + v*(A2 + v*(A3 + v*A4))); + + /* case 1: u1 = u rounded to 2^-43 absolute. Since u < 2^-8, + * u1 has at most 35 bits, and F*u1 is exact, as F has < 8 bits. + * It also adds exactly to |m*log2_hi + log_F_head[j] | < 750 + */ + if (m | j) + u1 = u + 513, u1 -= 513; + + /* case 2: |1-x| < 1/256. The m- and j- dependent terms are zero; + * u1 = u to 24 bits. + */ + else + u1 = u, TRUNC(u1); + u2 = (2.0*(f - F*u1) - u1*f) * g; + /* u1 + u2 = 2f/(2F+f) to extra precision. */ + + /* log(x) = log(2^m*F*(1+f/F)) = */ + /* (m*log2_hi+logF_head[j]+u1) + (m*log2_lo+logF_tail[j]+q); */ + /* (exact) + (tiny) */ + + u1 += m*logF_head[N] + logF_head[j]; /* exact */ + u2 = (u2 + logF_tail[j]) + q; /* tiny */ + u2 += logF_tail[N]*m; + return (u1 + u2); +} + +/* + * Extra precision variant, returning struct {double a, b;}; + * log(x) = a+b to 63 bits, with a is rounded to 26 bits. + */ +struct Double +#ifdef _ANSI_SOURCE +__log__D(double x) +#else +__log__D(x) double x; +#endif +{ + int m, j; + double F, f, g, q, u, v, u2, one = 1.0; + volatile double u1; + struct Double r; + + /* Argument reduction: 1 <= g < 2; x/2^m = g; */ + /* y = F*(1 + f/F) for |f| <= 2^-8 */ + + m = logb(x); + g = ldexp(x, -m); + if (_IEEE && m == -1022) { + j = logb(g), m += j; + g = ldexp(g, -j); + } + j = N*(g-1) + .5; + F = (1.0/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 + v*A4))); + if (m | j) + u1 = u + 513, u1 -= 513; + else + u1 = u, TRUNC(u1); + u2 = (2.0*(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 = u1 + u2; /* Only difference is here */ + TRUNC(r.a); + r.b = (u1 - r.a) + u2; + return (r); +} |