xref: /freebsd-11.0-release/lib/msun/ld80/s_expl.c

/*-
 * Copyright (c) 2009-2013 Steven G. Kargl
 * 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.
 *
 * Optimized by Bruce D. Evans.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD: head/lib/msun/ld80/s_expl.c 251328 2013-06-03 18:07:04Z kargl $");

/**
 * Compute the exponential of x for Intel 80-bit format.  This is based on:
 *
 *   PTP Tang, "Table-driven implementation of the exponential function
 *   in IEEE floating-point arithmetic," ACM Trans. Math. Soft., 15,
 *   144-157 (1989).
 *
 * where the 32 table entries have been expanded to INTERVALS (see below).
 */

#include <float.h>

#ifdef __i386__
#include <ieeefp.h>
#endif

#include "fpmath.h"
#include "math.h"
#include "math_private.h"

#define	INTERVALS	128
#define	LOG2_INTERVALS	7
#define	BIAS	(LDBL_MAX_EXP - 1)

static const long double
huge = 0x1p10000L,
twom10000 = 0x1p-10000L;
/* XXX Prevent gcc from erroneously constant folding this: */
static volatile const long double tiny = 0x1p-10000L;

static const union IEEEl2bits
/* log(2**16384 - 0.5) rounded towards zero: */
/* log(2**16384 - 0.5 + 1) rounded towards zero for expm1l() is the same: */
o_thresholdu = LD80C(0xb17217f7d1cf79ab, 13,  11356.5234062941439488L),
#define o_threshold	 (o_thresholdu.e)
/* log(2**(-16381-64-1)) rounded towards zero: */
u_thresholdu = LD80C(0xb21dfe7f09e2baa9, 13, -11399.4985314888605581L);
#define u_threshold	 (u_thresholdu.e)

static const double
/*
 * ln2/INTERVALS = L1+L2 (hi+lo decomposition for multiplication).  L1 must
 * have at least 22 (= log2(|LDBL_MIN_EXP-extras|) + log2(INTERVALS)) lowest
 * bits zero so that multiplication of it by n is exact.
 */
INV_L = 1.8466496523378731e+2,		/*  0x171547652b82fe.0p-45 */
L1 =  5.4152123484527692e-3,		/*  0x162e42ff000000.0p-60 */
L2 = -3.2819649005320973e-13,		/* -0x1718432a1b0e26.0p-94 */
/*
 * Domain [-0.002708, 0.002708], range ~[-5.7136e-24, 5.7110e-24]:
 * |exp(x) - p(x)| < 2**-77.2
 * (0.002708 is ln2/(2*INTERVALS) rounded up a little).
 */
A2 =  0.5,
A3 =  1.6666666666666119e-1,		/*  0x15555555555490.0p-55 */
A4 =  4.1666666666665887e-2,		/*  0x155555555554e5.0p-57 */
A5 =  8.3333354987869413e-3,		/*  0x1111115b789919.0p-59 */
A6 =  1.3888891738560272e-3;		/*  0x16c16c651633ae.0p-62 */

/*
 * 2^(i/INTERVALS) for i in [0,INTERVALS] is represented by two values where
 * the first 53 bits of the significand are stored in hi and the next 53
 * bits are in lo.  Tang's paper states that the trailing 6 bits of hi must
 * be zero for his algorithm in both single and double precision, because
 * the table is re-used in the implementation of expm1() where a floating
 * point addition involving hi must be exact.  Here hi is double, so
 * converting it to long double gives 11 trailing zero bits.
 */
static const struct {
	double	hi;
	double	lo;
} tbl[INTERVALS] = {
	0x1p+0, 0x0p+0,
	0x1.0163da9fb3335p+0, 0x1.b61299ab8cdb7p-54,
	0x1.02c9a3e778060p+0, 0x1.dcdef95949ef4p-53,
	0x1.04315e86e7f84p+0, 0x1.7ae71f3441b49p-53,
	0x1.059b0d3158574p+0, 0x1.d73e2a475b465p-55,
	0x1.0706b29ddf6ddp+0, 0x1.8db880753b0f6p-53,
	0x1.0874518759bc8p+0, 0x1.186be4bb284ffp-57,
	0x1.09e3ecac6f383p+0, 0x1.1487818316136p-54,
	0x1.0b5586cf9890fp+0, 0x1.8a62e4adc610bp-54,
	0x1.0cc922b7247f7p+0, 0x1.01edc16e24f71p-54,
	0x1.0e3ec32d3d1a2p+0, 0x1.03a1727c57b53p-59,
	0x1.0fb66affed31ap+0, 0x1.e464123bb1428p-53,
	0x1.11301d0125b50p+0, 0x1.49d77e35db263p-53,
	0x1.12abdc06c31cbp+0, 0x1.f72575a649ad2p-53,
	0x1.1429aaea92ddfp+0, 0x1.66820328764b1p-53,
	0x1.15a98c8a58e51p+0, 0x1.2406ab9eeab0ap-55,
	0x1.172b83c7d517ap+0, 0x1.b9bef918a1d63p-53,
	0x1.18af9388c8de9p+0, 0x1.777ee1734784ap-53,
	0x1.1a35beb6fcb75p+0, 0x1.e5b4c7b4968e4p-55,
	0x1.1bbe084045cd3p+0, 0x1.3563ce56884fcp-53,
	0x1.1d4873168b9aap+0, 0x1.e016e00a2643cp-54,
	0x1.1ed5022fcd91cp+0, 0x1.71033fec2243ap-53,
	0x1.2063b88628cd6p+0, 0x1.dc775814a8495p-55,
	0x1.21f49917ddc96p+0, 0x1.2a97e9494a5eep-55,
	0x1.2387a6e756238p+0, 0x1.9b07eb6c70573p-54,
	0x1.251ce4fb2a63fp+0, 0x1.ac155bef4f4a4p-55,
	0x1.26b4565e27cddp+0, 0x1.2bd339940e9d9p-55,
	0x1.284dfe1f56380p+0, 0x1.2d9e2b9e07941p-53,
	0x1.29e9df51fdee1p+0, 0x1.612e8afad1255p-55,
	0x1.2b87fd0dad98fp+0, 0x1.fbbd48ca71f95p-53,
	0x1.2d285a6e4030bp+0, 0x1.0024754db41d5p-54,
	0x1.2ecafa93e2f56p+0, 0x1.1ca0f45d52383p-56,
	0x1.306fe0a31b715p+0, 0x1.6f46ad23182e4p-55,
	0x1.32170fc4cd831p+0, 0x1.a9ce78e18047cp-55,
	0x1.33c08b26416ffp+0, 0x1.32721843659a6p-54,
	0x1.356c55f929ff0p+0, 0x1.928c468ec6e76p-53,
	0x1.371a7373aa9cap+0, 0x1.4e28aa05e8a8fp-53,
	0x1.38cae6d05d865p+0, 0x1.0b53961b37da2p-53,
	0x1.3a7db34e59ff6p+0, 0x1.d43792533c144p-53,
	0x1.3c32dc313a8e4p+0, 0x1.08003e4516b1ep-53,
	0x1.3dea64c123422p+0, 0x1.ada0911f09ebcp-55,
	0x1.3fa4504ac801bp+0, 0x1.417ee03548306p-53,
	0x1.4160a21f72e29p+0, 0x1.f0864b71e7b6cp-53,
	0x1.431f5d950a896p+0, 0x1.b8e088728219ap-53,
	0x1.44e086061892dp+0, 0x1.89b7a04ef80d0p-59,
	0x1.46a41ed1d0057p+0, 0x1.c944bd1648a76p-54,
	0x1.486a2b5c13cd0p+0, 0x1.3c1a3b69062f0p-56,
	0x1.4a32af0d7d3dep+0, 0x1.9cb62f3d1be56p-54,
	0x1.4bfdad5362a27p+0, 0x1.d4397afec42e2p-56,
	0x1.4dcb299fddd0dp+0, 0x1.8ecdbbc6a7833p-54,
	0x1.4f9b2769d2ca6p+0, 0x1.5a67b16d3540ep-53,
	0x1.516daa2cf6641p+0, 0x1.8225ea5909b04p-53,
	0x1.5342b569d4f81p+0, 0x1.be1507893b0d5p-53,
	0x1.551a4ca5d920ep+0, 0x1.8a5d8c4048699p-53,
	0x1.56f4736b527dap+0, 0x1.9bb2c011d93adp-54,
	0x1.58d12d497c7fdp+0, 0x1.295e15b9a1de8p-55,
	0x1.5ab07dd485429p+0, 0x1.6324c054647adp-54,
	0x1.5c9268a5946b7p+0, 0x1.c4b1b816986a2p-60,
	0x1.5e76f15ad2148p+0, 0x1.ba6f93080e65ep-54,
	0x1.605e1b976dc08p+0, 0x1.60edeb25490dcp-53,
	0x1.6247eb03a5584p+0, 0x1.63e1f40dfa5b5p-53,
	0x1.6434634ccc31fp+0, 0x1.8edf0e2989db3p-53,
	0x1.6623882552224p+0, 0x1.224fb3c5371e6p-53,
	0x1.68155d44ca973p+0, 0x1.038ae44f73e65p-57,
	0x1.6a09e667f3bccp+0, 0x1.21165f626cdd5p-53,
	0x1.6c012750bdabep+0, 0x1.daed533001e9ep-53,
	0x1.6dfb23c651a2ep+0, 0x1.e441c597c3775p-53,
	0x1.6ff7df9519483p+0, 0x1.9f0fc369e7c42p-53,
	0x1.71f75e8ec5f73p+0, 0x1.ba46e1e5de15ap-53,
	0x1.73f9a48a58173p+0, 0x1.7ab9349cd1562p-53,
	0x1.75feb564267c8p+0, 0x1.7edd354674916p-53,
	0x1.780694fde5d3fp+0, 0x1.866b80a02162dp-54,
	0x1.7a11473eb0186p+0, 0x1.afaa2047ed9b4p-53,
	0x1.7c1ed0130c132p+0, 0x1.f124cd1164dd6p-54,
	0x1.7e2f336cf4e62p+0, 0x1.05d02ba15797ep-56,
	0x1.80427543e1a11p+0, 0x1.6c1bccec9346bp-53,
	0x1.82589994cce12p+0, 0x1.159f115f56694p-53,
	0x1.8471a4623c7acp+0, 0x1.9ca5ed72f8c81p-53,
	0x1.868d99b4492ecp+0, 0x1.01c83b21584a3p-53,
	0x1.88ac7d98a6699p+0, 0x1.994c2f37cb53ap-54,
	0x1.8ace5422aa0dbp+0, 0x1.6e9f156864b27p-54,
	0x1.8cf3216b5448bp+0, 0x1.de55439a2c38bp-53,
	0x1.8f1ae99157736p+0, 0x1.5cc13a2e3976cp-55,
	0x1.9145b0b91ffc5p+0, 0x1.114c368d3ed6ep-53,
	0x1.93737b0cdc5e4p+0, 0x1.e8a0387e4a814p-53,
	0x1.95a44cbc8520ep+0, 0x1.d36906d2b41f9p-53,
	0x1.97d829fde4e4fp+0, 0x1.173d241f23d18p-53,
	0x1.9a0f170ca07b9p+0, 0x1.7462137188ce7p-53,
	0x1.9c49182a3f090p+0, 0x1.c7c46b071f2bep-56,
	0x1.9e86319e32323p+0, 0x1.824ca78e64c6ep-56,
	0x1.a0c667b5de564p+0, 0x1.6535b51719567p-53,
	0x1.a309bec4a2d33p+0, 0x1.6305c7ddc36abp-54,
	0x1.a5503b23e255cp+0, 0x1.1684892395f0fp-53,
	0x1.a799e1330b358p+0, 0x1.bcb7ecac563c7p-54,
	0x1.a9e6b5579fdbfp+0, 0x1.0fac90ef7fd31p-54,
	0x1.ac36bbfd3f379p+0, 0x1.81b72cd4624ccp-53,
	0x1.ae89f995ad3adp+0, 0x1.7a1cd345dcc81p-54,
	0x1.b0e07298db665p+0, 0x1.2108559bf8deep-53,
	0x1.b33a2b84f15fap+0, 0x1.ed7fa1cf7b290p-53,
	0x1.b59728de55939p+0, 0x1.1c7102222c90ep-53,
	0x1.b7f76f2fb5e46p+0, 0x1.d54f610356a79p-53,
	0x1.ba5b030a10649p+0, 0x1.0819678d5eb69p-53,
	0x1.bcc1e904bc1d2p+0, 0x1.23dd07a2d9e84p-55,
	0x1.bf2c25bd71e08p+0, 0x1.0811ae04a31c7p-53,
	0x1.c199bdd85529cp+0, 0x1.11065895048ddp-55,
	0x1.c40ab5fffd07ap+0, 0x1.b4537e083c60ap-54,
	0x1.c67f12e57d14bp+0, 0x1.2884dff483cadp-54,
	0x1.c8f6d9406e7b5p+0, 0x1.1acbc48805c44p-56,
	0x1.cb720dcef9069p+0, 0x1.503cbd1e949dbp-56,
	0x1.cdf0b555dc3f9p+0, 0x1.889f12b1f58a3p-53,
	0x1.d072d4a07897bp+0, 0x1.1a1e45e4342b2p-53,
	0x1.d2f87080d89f1p+0, 0x1.15bc247313d44p-53,
	0x1.d5818dcfba487p+0, 0x1.2ed02d75b3707p-55,
	0x1.d80e316c98397p+0, 0x1.7709f3a09100cp-53,
	0x1.da9e603db3285p+0, 0x1.c2300696db532p-54,
	0x1.dd321f301b460p+0, 0x1.2da5778f018c3p-54,
	0x1.dfc97337b9b5ep+0, 0x1.72d195873da52p-53,
	0x1.e264614f5a128p+0, 0x1.424ec3f42f5b5p-53,
	0x1.e502ee78b3ff6p+0, 0x1.39e8980a9cc8fp-55,
	0x1.e7a51fbc74c83p+0, 0x1.2d522ca0c8de2p-54,
	0x1.ea4afa2a490d9p+0, 0x1.0b1ee7431ebb6p-53,
	0x1.ecf482d8e67f0p+0, 0x1.1b60625f7293ap-53,
	0x1.efa1bee615a27p+0, 0x1.dc7f486a4b6b0p-54,
	0x1.f252b376bba97p+0, 0x1.3a1a5bf0d8e43p-54,
	0x1.f50765b6e4540p+0, 0x1.9d3e12dd8a18bp-54,
	0x1.f7bfdad9cbe13p+0, 0x1.1227697fce57bp-53,
	0x1.fa7c1819e90d8p+0, 0x1.74853f3a5931ep-55,
	0x1.fd3c22b8f71f1p+0, 0x1.2eb74966579e7p-57
};

long double
expl(long double x)
{
	union IEEEl2bits u, v;
	long double fn, q, r, r1, r2, t, t23, t45, twopk, twopkp10000, z;
	int k, n, n2;
	uint16_t hx, ix;

	/* Filter out exceptional cases. */
	u.e = x;
	hx = u.xbits.expsign;
	ix = hx & 0x7fff;
	if (ix >= BIAS + 13) {		/* |x| >= 8192 or x is NaN */
		if (ix == BIAS + LDBL_MAX_EXP) {
			if (hx & 0x8000 && u.xbits.man == 1ULL << 63)
				return (0.0L);	/* x is -Inf */
			return (x + x); /* x is +Inf, NaN or unsupported */
		}
		if (x > o_threshold)
			return (huge * huge);
		if (x < u_threshold)
			return (tiny * tiny);
	} else if (ix < BIAS - 66) {	/* |x| < 0x1p-66 */
					/* includes pseudo-denormals */
		if (huge + x > 1.0L)	/* trigger inexact iff x != 0 */
			return (1.0L + x);
	}

	ENTERI();

	/* Reduce x to (k*ln2 + midpoint[n2] + r1 + r2). */
	/* Use a specialized rint() to get fn.  Assume round-to-nearest. */
	fn = x * INV_L + 0x1.8p63 - 0x1.8p63;
	r = x - fn * L1 - fn * L2;	/* r = r1 + r2 done independently. */
#if defined(HAVE_EFFICIENT_IRINTL)
	n = irintl(fn);
#elif defined(HAVE_EFFICIENT_IRINT)
	n = irint(fn);
#else
	n = (int)fn;
#endif
	n2 = (unsigned)n % INTERVALS;
	/* Depend on the sign bit being propagated: */
	k = n >> LOG2_INTERVALS;
	r1 = x - fn * L1;
	r2 = -fn * L2;

	/* Prepare scale factors. */
	v.xbits.man = 1ULL << 63;
	if (k >= LDBL_MIN_EXP) {
		v.xbits.expsign = BIAS + k;
		twopk = v.e;
	} else {
		v.xbits.expsign = BIAS + k + 10000;
		twopkp10000 = v.e;
	}

	/* Evaluate expl(midpoint[n2] + r1 + r2) = tbl[n2] * expl(r1 + r2). */
	/* Here q = q(r), not q(r1), since r1 is lopped like L1. */
	t45 = r * P5 + P4;
	z = r * r;
	t23 = r * P3 + P2;
	q = r2 + z * t23 + z * z * t45 + z * z * z * P6;
	t = (long double)tbl[n2].lo + tbl[n2].hi;
	t = tbl[n2].lo + t * (q + r1) + tbl[n2].hi;

	/* Scale by 2**k. */
	if (k >= LDBL_MIN_EXP) {
		if (k == LDBL_MAX_EXP)
			RETURNI(t * 2.0L * 0x1p16383L);
		RETURNI(t * twopk);
	} else {
		RETURNI(t * twopkp10000 * twom10000);
	}
}