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c55e0c62a1
freebsd/lib/msun/ld80/s_exp2l.c
Bruce Evans f01bfe5c6d Fix exp2*(x) on signaling NaNs by returning x+x as usual. 
This has the side effect of confusing gcc-4.2.1's optimizer into more
often doing the right thing.  When it does the wrong thing here, it
seems to be mainly making too many copies of x with dependency chains.
This effect is tiny on amd64, but in some cases on i386 it is enormous.
E.g., on i386 (A64) with -O1, the current version of exp2() should
take about 50 cycles, but took 83 cycles before this change and 66
cycles after this change.  exp2f() with -O1 only speeded up from 51
to 47 cycles.  (exp2f() should take about 40 cycles, on an Athlon in
either i386 or amd64 mode, and now takes 42 on amd64).  exp2l() with
-O1 slowed down from 155 cycles to 123 for some args; this is unimportant
since the i386 exp2l() is a fake; the wrong thing for it seems to
involve branch misprediction.
2008-02-13 10:44:44 +00:00

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/*-
* Copyright (c) 2005-2008 David Schultz <das@FreeBSD.ORG>
* 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.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <float.h>
#include <stdint.h>
#ifdef __i386__
#include <ieeefp.h>
#endif
#include "fpmath.h"
#include "math.h"
#define TBLBITS 7
#define TBLSIZE (1 << TBLBITS)
#define BIAS (LDBL_MAX_EXP - 1)
#define EXPMASK (BIAS + LDBL_MAX_EXP)
static const long double huge = 0x1p10000L;
#if 0 /* XXX Prevent gcc from erroneously constant folding this. */
static const long double twom10000 = 0x1p-10000L;
#else
static volatile long double twom10000 = 0x1p-10000L;
#endif
static const double
redux = 0x1.8p63 / TBLSIZE,
P1 = 0x1.62e42fefa39efp-1,
P2 = 0x1.ebfbdff82c58fp-3,
P3 = 0x1.c6b08d7049fap-5,
P4 = 0x1.3b2ab6fba4da5p-7,
P5 = 0x1.5d8804780a736p-10,
P6 = 0x1.430918835e33dp-13;
static const double tbl[TBLSIZE * 2] = {
0x1.6a09e667f3bcdp-1, -0x1.bdd3413b2648p-55,
0x1.6c012750bdabfp-1, -0x1.2895667ff0cp-57,
0x1.6dfb23c651a2fp-1, -0x1.bbe3a683c88p-58,
0x1.6ff7df9519484p-1, -0x1.83c0f25860fp-56,
0x1.71f75e8ec5f74p-1, -0x1.16e4786887bp-56,
0x1.73f9a48a58174p-1, -0x1.0a8d96c65d5p-55,
0x1.75feb564267c9p-1, -0x1.0245957316ep-55,
0x1.780694fde5d3fp-1, 0x1.866b80a0216p-55,
0x1.7a11473eb0187p-1, -0x1.41577ee0499p-56,
0x1.7c1ed0130c132p-1, 0x1.f124cd1164ep-55,
0x1.7e2f336cf4e62p-1, 0x1.05d02ba157ap-57,
0x1.80427543e1a12p-1, -0x1.27c86626d97p-55,
0x1.82589994cce13p-1, -0x1.d4c1dd41533p-55,
0x1.8471a4623c7adp-1, -0x1.8d684a341cep-56,
0x1.868d99b4492edp-1, -0x1.fc6f89bd4f68p-55,
0x1.88ac7d98a6699p-1, 0x1.994c2f37cb5p-55,
0x1.8ace5422aa0dbp-1, 0x1.6e9f156864bp-55,
0x1.8cf3216b5448cp-1, -0x1.0d55e32e9e4p-57,
0x1.8f1ae99157736p-1, 0x1.5cc13a2e397p-56,
0x1.9145b0b91ffc6p-1, -0x1.dd6792e5825p-55,
0x1.93737b0cdc5e5p-1, -0x1.75fc781b58p-58,
0x1.95a44cbc8520fp-1, -0x1.64b7c96a5fp-57,
0x1.97d829fde4e5p-1, -0x1.d185b7c1b86p-55,
0x1.9a0f170ca07bap-1, -0x1.173bd91cee6p-55,
0x1.9c49182a3f09p-1, 0x1.c7c46b071f2p-57,
0x1.9e86319e32323p-1, 0x1.824ca78e64cp-57,
0x1.a0c667b5de565p-1, -0x1.359495d1cd5p-55,
0x1.a309bec4a2d33p-1, 0x1.6305c7ddc368p-55,
0x1.a5503b23e255dp-1, -0x1.d2f6edb8d42p-55,
0x1.a799e1330b358p-1, 0x1.bcb7ecac564p-55,
0x1.a9e6b5579fdbfp-1, 0x1.0fac90ef7fdp-55,
0x1.ac36bbfd3f37ap-1, -0x1.f9234cae76dp-56,
0x1.ae89f995ad3adp-1, 0x1.7a1cd345dcc8p-55,
0x1.b0e07298db666p-1, -0x1.bdef54c80e4p-55,
0x1.b33a2b84f15fbp-1, -0x1.2805e3084d8p-58,
0x1.b59728de5593ap-1, -0x1.c71dfbbba6ep-55,
0x1.b7f76f2fb5e47p-1, -0x1.5584f7e54acp-57,
0x1.ba5b030a1064ap-1, -0x1.efcd30e5429p-55,
0x1.bcc1e904bc1d2p-1, 0x1.23dd07a2d9fp-56,
0x1.bf2c25bd71e09p-1, -0x1.efdca3f6b9c8p-55,
0x1.c199bdd85529cp-1, 0x1.11065895049p-56,
0x1.c40ab5fffd07ap-1, 0x1.b4537e083c6p-55,
0x1.c67f12e57d14bp-1, 0x1.2884dff483c8p-55,
0x1.c8f6d9406e7b5p-1, 0x1.1acbc48805cp-57,
0x1.cb720dcef9069p-1, 0x1.503cbd1e94ap-57,
0x1.cdf0b555dc3fap-1, -0x1.dd83b53829dp-56,
0x1.d072d4a07897cp-1, -0x1.cbc3743797a8p-55,
0x1.d2f87080d89f2p-1, -0x1.d487b719d858p-55,
0x1.d5818dcfba487p-1, 0x1.2ed02d75b37p-56,
0x1.d80e316c98398p-1, -0x1.11ec18bedep-55,
0x1.da9e603db3285p-1, 0x1.c2300696db5p-55,
0x1.dd321f301b46p-1, 0x1.2da5778f019p-55,
0x1.dfc97337b9b5fp-1, -0x1.1a5cd4f184b8p-55,
0x1.e264614f5a129p-1, -0x1.7b627817a148p-55,
0x1.e502ee78b3ff6p-1, 0x1.39e8980a9cdp-56,
0x1.e7a51fbc74c83p-1, 0x1.2d522ca0c8ep-55,
0x1.ea4afa2a490dap-1, -0x1.e9c23179c288p-55,
0x1.ecf482d8e67f1p-1, -0x1.c93f3b411ad8p-55,
0x1.efa1bee615a27p-1, 0x1.dc7f486a4b68p-55,
0x1.f252b376bba97p-1, 0x1.3a1a5bf0d8e8p-55,
0x1.f50765b6e454p-1, 0x1.9d3e12dd8a18p-55,
0x1.f7bfdad9cbe14p-1, -0x1.dbb12d00635p-55,
0x1.fa7c1819e90d8p-1, 0x1.74853f3a593p-56,
0x1.fd3c22b8f71f1p-1, 0x1.2eb74966578p-58,
0x1p+0, 0x0p+0,
0x1.0163da9fb3335p+0, 0x1.b61299ab8cd8p-54,
0x1.02c9a3e778061p+0, -0x1.19083535b08p-56,
0x1.04315e86e7f85p+0, -0x1.0a31c1977c98p-54,
0x1.059b0d3158574p+0, 0x1.d73e2a475b4p-55,
0x1.0706b29ddf6dep+0, -0x1.c91dfe2b13cp-55,
0x1.0874518759bc8p+0, 0x1.186be4bb284p-57,
0x1.09e3ecac6f383p+0, 0x1.14878183161p-54,
0x1.0b5586cf9890fp+0, 0x1.8a62e4adc61p-54,
0x1.0cc922b7247f7p+0, 0x1.01edc16e24f8p-54,
0x1.0e3ec32d3d1a2p+0, 0x1.03a1727c58p-59,
0x1.0fb66affed31bp+0, -0x1.b9bedc44ebcp-57,
0x1.11301d0125b51p+0, -0x1.6c51039449bp-54,
0x1.12abdc06c31ccp+0, -0x1.1b514b36ca8p-58,
0x1.1429aaea92dep+0, -0x1.32fbf9af1368p-54,
0x1.15a98c8a58e51p+0, 0x1.2406ab9eeabp-55,
0x1.172b83c7d517bp+0, -0x1.19041b9d78ap-55,
0x1.18af9388c8deap+0, -0x1.11023d1970f8p-54,
0x1.1a35beb6fcb75p+0, 0x1.e5b4c7b4969p-55,
0x1.1bbe084045cd4p+0, -0x1.95386352ef6p-54,
0x1.1d4873168b9aap+0, 0x1.e016e00a264p-54,
0x1.1ed5022fcd91dp+0, -0x1.1df98027bb78p-54,
0x1.2063b88628cd6p+0, 0x1.dc775814a85p-55,
0x1.21f49917ddc96p+0, 0x1.2a97e9494a6p-55,
0x1.2387a6e756238p+0, 0x1.9b07eb6c7058p-54,
0x1.251ce4fb2a63fp+0, 0x1.ac155bef4f5p-55,
0x1.26b4565e27cddp+0, 0x1.2bd339940eap-55,
0x1.284dfe1f56381p+0, -0x1.a4c3a8c3f0d8p-54,
0x1.29e9df51fdee1p+0, 0x1.612e8afad12p-55,
0x1.2b87fd0dad99p+0, -0x1.10adcd6382p-59,
0x1.2d285a6e4030bp+0, 0x1.0024754db42p-54,
0x1.2ecafa93e2f56p+0, 0x1.1ca0f45d524p-56,
0x1.306fe0a31b715p+0, 0x1.6f46ad23183p-55,
0x1.32170fc4cd831p+0, 0x1.a9ce78e1804p-55,
0x1.33c08b26416ffp+0, 0x1.327218436598p-54,
0x1.356c55f929ff1p+0, -0x1.b5cee5c4e46p-55,
0x1.371a7373aa9cbp+0, -0x1.63aeabf42ebp-54,
0x1.38cae6d05d866p+0, -0x1.e958d3c99048p-54,
0x1.3a7db34e59ff7p+0, -0x1.5e436d661f6p-56,
0x1.3c32dc313a8e5p+0, -0x1.efff8375d2ap-54,
0x1.3dea64c123422p+0, 0x1.ada0911f09fp-55,
0x1.3fa4504ac801cp+0, -0x1.7d023f956fap-54,
0x1.4160a21f72e2ap+0, -0x1.ef3691c309p-58,
0x1.431f5d950a897p+0, -0x1.1c7dde35f7ap-55,
0x1.44e086061892dp+0, 0x1.89b7a04ef8p-59,
0x1.46a41ed1d0057p+0, 0x1.c944bd1648a8p-54,
0x1.486a2b5c13cdp+0, 0x1.3c1a3b69062p-56,
0x1.4a32af0d7d3dep+0, 0x1.9cb62f3d1be8p-54,
0x1.4bfdad5362a27p+0, 0x1.d4397afec42p-56,
0x1.4dcb299fddd0dp+0, 0x1.8ecdbbc6a78p-54,
0x1.4f9b2769d2ca7p+0, -0x1.4b309d25958p-54,
0x1.516daa2cf6642p+0, -0x1.f768569bd94p-55,
0x1.5342b569d4f82p+0, -0x1.07abe1db13dp-55,
0x1.551a4ca5d920fp+0, -0x1.d689cefede6p-55,
0x1.56f4736b527dap+0, 0x1.9bb2c011d938p-54,
0x1.58d12d497c7fdp+0, 0x1.295e15b9a1ep-55,
0x1.5ab07dd485429p+0, 0x1.6324c0546478p-54,
0x1.5c9268a5946b7p+0, 0x1.c4b1b81698p-60,
0x1.5e76f15ad2148p+0, 0x1.ba6f93080e68p-54,
0x1.605e1b976dc09p+0, -0x1.3e2429b56de8p-54,
0x1.6247eb03a5585p+0, -0x1.383c17e40b48p-54,
0x1.6434634ccc32p+0, -0x1.c483c759d89p-55,
0x1.6623882552225p+0, -0x1.bb60987591cp-54,
0x1.68155d44ca973p+0, 0x1.038ae44f74p-57,
};
/*
* exp2l(x): compute the base 2 exponential of x
*
* Accuracy: Peak error < 0.511 ulp.
*
* Method: (equally-spaced tables)
*
* Reduce x:
* x = 2**k + y, for integer k and |y| <= 1/2.
* Thus we have exp2l(x) = 2**k * exp2(y).
*
* Reduce y:
* y = i/TBLSIZE + z for integer i near y * TBLSIZE.
* Thus we have exp2(y) = exp2(i/TBLSIZE) * exp2(z),
* with |z| <= 2**-(TBLBITS+1).
*
* We compute exp2(i/TBLSIZE) via table lookup and exp2(z) via a
* degree-6 minimax polynomial with maximum error under 2**-69.
* The table entries each have 104 bits of accuracy, encoded as
* a pair of double precision values.
*/
long double
exp2l(long double x)
{
union IEEEl2bits u, v;
long double r, twopk, twopkp10000, z;
uint32_t hx, ix, i0;
int k;
/* Filter out exceptional cases. */
u.e = x;
hx = u.xbits.expsign;
ix = hx & EXPMASK;
if (ix >= BIAS + 14) { /* |x| >= 16384 or x is NaN */
if (ix == BIAS + LDBL_MAX_EXP) {
if (u.xbits.man != 1ULL << 63 || (hx & 0x8000) == 0)
return (x + x); /* x is +Inf or NaN */
else
return (0.0); /* x is -Inf */
}
if (x >= 16384)
return (huge * huge); /* overflow */
if (x <= -16446)
return (twom10000 * twom10000); /* underflow */
} else if (ix <= BIAS - 66) { /* |x| < 0x1p-66 */
return (1.0 + x);
}
#ifdef __i386__
/*
* The default precision on i386 is 53 bits, so long doubles are
* broken. Call exp2() to get an accurate (double precision) result.
*/
if (fpgetprec() != FP_PE)
return (exp2(x));
#endif
/*
* Reduce x, computing z, i0, and k. The low bits of x + redux
* contain the 16-bit integer part of the exponent (k) followed by
* TBLBITS fractional bits (i0). We use bit tricks to extract these
* as integers, then set z to the remainder.
*
* Example: Suppose x is 0xabc.123456p0 and TBLBITS is 8.
* Then the low-order word of x + redux is 0x000abc12,
* We split this into k = 0xabc and i0 = 0x12 (adjusted to
* index into the table), then we compute z = 0x0.003456p0.
*
* XXX If the exponent is negative, the computation of k depends on
* '>>' doing sign extension.
*/
u.e = x + redux;
i0 = u.bits.manl + TBLSIZE / 2;
k = (int)i0 >> TBLBITS;
i0 = (i0 & (TBLSIZE - 1)) << 1;
u.e -= redux;
z = x - u.e;
v.xbits.man = 1ULL << 63;
if (k >= LDBL_MIN_EXP) {
v.xbits.expsign = LDBL_MAX_EXP - 1 + k;
twopk = v.e;
} else {
v.xbits.expsign = LDBL_MAX_EXP - 1 + k + 10000;
twopkp10000 = v.e;
}
/* Compute r = exp2l(y) = exp2lt[i0] * p(z). */
long double t_hi = tbl[i0];
long double t_lo = tbl[i0 + 1];
/* XXX This gives > 1 ulp errors outside of FE_TONEAREST mode */
r = t_lo + (t_hi + t_lo) * z * (P1 + z * (P2 + z * (P3 + z * (P4
+ z * (P5 + z * P6))))) + t_hi;
/* Scale by 2**k. */
if (k >= LDBL_MIN_EXP) {
if (k == LDBL_MAX_EXP)
return (r * 2.0 * 0x1p16383L);
return (r * twopk);
} else {
return (r * twopkp10000 * twom10000);
}
}
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