d/freebsd-skq
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity
f5542795b9
freebsd-skq/lib/msun/ld128/s_exp2l.c

430 lines
12 KiB
C
Raw Normal View History

Implement exp2l(). There is one version for machines with 80-bit long doubles (i386, amd64, ia64) and one for machines with 128-bit long doubles (sparc64). Other platforms use the double version. I've only done runtime testing on i386. Thanks to bde@ for helpful discussions and bugfixes.
2008-01-18 21:42:46 +00:00
/*-
lib: further adoption of SPDX licensing ID tags. Mainly focus on files that use BSD 2-Clause license, however the tool I was using mis-identified many licenses so this was mostly a manual - error prone - task. The Software Package Data Exchange (SPDX) group provides a specification to make it easier for automated tools to detect and summarize well known opensource licenses. We are gradually adopting the specification, noting that the tags are considered only advisory and do not, in any way, superceed or replace the license texts.
2017-11-26 02:00:33 +00:00
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
Implement exp2l(). There is one version for machines with 80-bit long doubles (i386, amd64, ia64) and one for machines with 128-bit long doubles (sparc64). Other platforms use the double version. I've only done runtime testing on i386. Thanks to bde@ for helpful discussions and bugfixes.
2008-01-18 21:42:46 +00:00
* 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>
#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)
Fix some regressions caused by the switch from gcc to clang. The fixes are workarounds for various symptoms of the problem described in clang bugs 3929, 8100, 8241, 10409, and 12958. The regression tests did their job: they failed, someone brought it up on the mailing lists, and then the issue got ignored for 6 months. Oops. There may still be some regressions for functions we don't have test coverage for yet.
2013-05-27 08:50:10 +00:00
static volatile long double
huge = 0x1p10000L,
twom10000 = 0x1p-10000L;
Implement exp2l(). There is one version for machines with 80-bit long doubles (i386, amd64, ia64) and one for machines with 128-bit long doubles (sparc64). Other platforms use the double version. I've only done runtime testing on i386. Thanks to bde@ for helpful discussions and bugfixes.
2008-01-18 21:42:46 +00:00
static const long double
P1 = 0x1.62e42fefa39ef35793c7673007e6p-1L,
P2 = 0x1.ebfbdff82c58ea86f16b06ec9736p-3L,
P3 = 0x1.c6b08d704a0bf8b33a762bad3459p-5L,
P4 = 0x1.3b2ab6fba4e7729ccbbe0b4f3fc2p-7L,
P5 = 0x1.5d87fe78a67311071dee13fd11d9p-10L,
P6 = 0x1.430912f86c7876f4b663b23c5fe5p-13L;
static const double
P7 = 0x1.ffcbfc588b041p-17,
P8 = 0x1.62c0223a5c7c7p-20,
P9 = 0x1.b52541ff59713p-24,
P10 = 0x1.e4cf56a391e22p-28,
redux = 0x1.8p112 / TBLSIZE;
static const long double tbl[TBLSIZE] = {
0x1.6a09e667f3bcc908b2fb1366dfeap-1L,
0x1.6c012750bdabeed76a99800f4edep-1L,
0x1.6dfb23c651a2ef220e2cbe1bc0d4p-1L,
0x1.6ff7df9519483cf87e1b4f3e1e98p-1L,
0x1.71f75e8ec5f73dd2370f2ef0b148p-1L,
0x1.73f9a48a58173bd5c9a4e68ab074p-1L,
0x1.75feb564267c8bf6e9aa33a489a8p-1L,
0x1.780694fde5d3f619ae02808592a4p-1L,
0x1.7a11473eb0186d7d51023f6ccb1ap-1L,
0x1.7c1ed0130c1327c49334459378dep-1L,
0x1.7e2f336cf4e62105d02ba1579756p-1L,
0x1.80427543e1a11b60de67649a3842p-1L,
0x1.82589994cce128acf88afab34928p-1L,
0x1.8471a4623c7acce52f6b97c6444cp-1L,
0x1.868d99b4492ec80e41d90ac2556ap-1L,
0x1.88ac7d98a669966530bcdf2d4cc0p-1L,
0x1.8ace5422aa0db5ba7c55a192c648p-1L,
0x1.8cf3216b5448bef2aa1cd161c57ap-1L,
0x1.8f1ae991577362b982745c72eddap-1L,
0x1.9145b0b91ffc588a61b469f6b6a0p-1L,
0x1.93737b0cdc5e4f4501c3f2540ae8p-1L,
0x1.95a44cbc8520ee9b483695a0e7fep-1L,
0x1.97d829fde4e4f8b9e920f91e8eb6p-1L,
0x1.9a0f170ca07b9ba3109b8c467844p-1L,
0x1.9c49182a3f0901c7c46b071f28dep-1L,
0x1.9e86319e323231824ca78e64c462p-1L,
0x1.a0c667b5de564b29ada8b8cabbacp-1L,
0x1.a309bec4a2d3358c171f770db1f4p-1L,
0x1.a5503b23e255c8b424491caf88ccp-1L,
0x1.a799e1330b3586f2dfb2b158f31ep-1L,
0x1.a9e6b5579fdbf43eb243bdff53a2p-1L,
0x1.ac36bbfd3f379c0db966a3126988p-1L,
0x1.ae89f995ad3ad5e8734d17731c80p-1L,
0x1.b0e07298db66590842acdfc6fb4ep-1L,
0x1.b33a2b84f15faf6bfd0e7bd941b0p-1L,
0x1.b59728de559398e3881111648738p-1L,
0x1.b7f76f2fb5e46eaa7b081ab53ff6p-1L,
0x1.ba5b030a10649840cb3c6af5b74cp-1L,
0x1.bcc1e904bc1d2247ba0f45b3d06cp-1L,
0x1.bf2c25bd71e088408d7025190cd0p-1L,
0x1.c199bdd85529c2220cb12a0916bap-1L,
0x1.c40ab5fffd07a6d14df820f17deap-1L,
0x1.c67f12e57d14b4a2137fd20f2a26p-1L,
0x1.c8f6d9406e7b511acbc48805c3f6p-1L,
0x1.cb720dcef90691503cbd1e949d0ap-1L,
0x1.cdf0b555dc3f9c44f8958fac4f12p-1L,
0x1.d072d4a07897b8d0f22f21a13792p-1L,
0x1.d2f87080d89f18ade123989ea50ep-1L,
0x1.d5818dcfba48725da05aeb66dff8p-1L,
0x1.d80e316c98397bb84f9d048807a0p-1L,
0x1.da9e603db3285708c01a5b6d480cp-1L,
0x1.dd321f301b4604b695de3c0630c0p-1L,
0x1.dfc97337b9b5eb968cac39ed284cp-1L,
0x1.e264614f5a128a12761fa17adc74p-1L,
0x1.e502ee78b3ff6273d130153992d0p-1L,
0x1.e7a51fbc74c834b548b2832378a4p-1L,
0x1.ea4afa2a490d9858f73a18f5dab4p-1L,
0x1.ecf482d8e67f08db0312fb949d50p-1L,
0x1.efa1bee615a27771fd21a92dabb6p-1L,
0x1.f252b376bba974e8696fc3638f24p-1L,
0x1.f50765b6e4540674f84b762861a6p-1L,
0x1.f7bfdad9cbe138913b4bfe72bd78p-1L,
0x1.fa7c1819e90d82e90a7e74b26360p-1L,
0x1.fd3c22b8f71f10975ba4b32bd006p-1L,
0x1.0000000000000000000000000000p+0L,
0x1.0163da9fb33356d84a66ae336e98p+0L,
0x1.02c9a3e778060ee6f7caca4f7a18p+0L,
0x1.04315e86e7f84bd738f9a20da442p+0L,
0x1.059b0d31585743ae7c548eb68c6ap+0L,
0x1.0706b29ddf6ddc6dc403a9d87b1ep+0L,
0x1.0874518759bc808c35f25d942856p+0L,
0x1.09e3ecac6f3834521e060c584d5cp+0L,
0x1.0b5586cf9890f6298b92b7184200p+0L,
0x1.0cc922b7247f7407b705b893dbdep+0L,
0x1.0e3ec32d3d1a2020742e4f8af794p+0L,
0x1.0fb66affed31af232091dd8a169ep+0L,
0x1.11301d0125b50a4ebbf1aed9321cp+0L,
0x1.12abdc06c31cbfb92bad324d6f84p+0L,
0x1.1429aaea92ddfb34101943b2588ep+0L,
0x1.15a98c8a58e512480d573dd562aep+0L,
0x1.172b83c7d517adcdf7c8c50eb162p+0L,
0x1.18af9388c8de9bbbf70b9a3c269cp+0L,
0x1.1a35beb6fcb753cb698f692d2038p+0L,
0x1.1bbe084045cd39ab1e72b442810ep+0L,
0x1.1d4873168b9aa7805b8028990be8p+0L,
0x1.1ed5022fcd91cb8819ff61121fbep+0L,
0x1.2063b88628cd63b8eeb0295093f6p+0L,
0x1.21f49917ddc962552fd29294bc20p+0L,
0x1.2387a6e75623866c1fadb1c159c0p+0L,
0x1.251ce4fb2a63f3582ab7de9e9562p+0L,
0x1.26b4565e27cdd257a673281d3068p+0L,
0x1.284dfe1f5638096cf15cf03c9fa0p+0L,
0x1.29e9df51fdee12c25d15f5a25022p+0L,
0x1.2b87fd0dad98ffddea46538fca24p+0L,
0x1.2d285a6e4030b40091d536d0733ep+0L,
0x1.2ecafa93e2f5611ca0f45d5239a4p+0L,
0x1.306fe0a31b7152de8d5a463063bep+0L,
0x1.32170fc4cd8313539cf1c3009330p+0L,
0x1.33c08b26416ff4c9c8610d96680ep+0L,
0x1.356c55f929ff0c94623476373be4p+0L,
0x1.371a7373aa9caa7145502f45452ap+0L,
0x1.38cae6d05d86585a9cb0d9bed530p+0L,
0x1.3a7db34e59ff6ea1bc9299e0a1fep+0L,
0x1.3c32dc313a8e484001f228b58cf0p+0L,
0x1.3dea64c12342235b41223e13d7eep+0L,
0x1.3fa4504ac801ba0bf701aa417b9cp+0L,
0x1.4160a21f72e29f84325b8f3dbacap+0L,
0x1.431f5d950a896dc704439410b628p+0L,
0x1.44e086061892d03136f409df0724p+0L,
0x1.46a41ed1d005772512f459229f0ap+0L,
0x1.486a2b5c13cd013c1a3b69062f26p+0L,
0x1.4a32af0d7d3de672d8bcf46f99b4p+0L,
0x1.4bfdad5362a271d4397afec42e36p+0L,
0x1.4dcb299fddd0d63b36ef1a9e19dep+0L,
0x1.4f9b2769d2ca6ad33d8b69aa0b8cp+0L,
0x1.516daa2cf6641c112f52c84d6066p+0L,
0x1.5342b569d4f81df0a83c49d86bf4p+0L,
0x1.551a4ca5d920ec52ec620243540cp+0L,
0x1.56f4736b527da66ecb004764e61ep+0L,
0x1.58d12d497c7fd252bc2b7343d554p+0L,
0x1.5ab07dd48542958c93015191e9a8p+0L,
0x1.5c9268a5946b701c4b1b81697ed4p+0L,
0x1.5e76f15ad21486e9be4c20399d12p+0L,
0x1.605e1b976dc08b076f592a487066p+0L,
0x1.6247eb03a5584b1f0fa06fd2d9eap+0L,
0x1.6434634ccc31fc76f8714c4ee122p+0L,
0x1.66238825522249127d9e29b92ea2p+0L,
0x1.68155d44ca973081c57227b9f69ep+0L,
};
static const float eps[TBLSIZE] = {
-0x1.5c50p-101,
-0x1.5d00p-106,
0x1.8e90p-102,
-0x1.5340p-103,
0x1.1bd0p-102,
-0x1.4600p-105,
-0x1.7a40p-104,
0x1.d590p-102,
-0x1.d590p-101,
0x1.b100p-103,
-0x1.0d80p-105,
0x1.6b00p-103,
-0x1.9f00p-105,
0x1.c400p-103,
0x1.e120p-103,
-0x1.c100p-104,
-0x1.9d20p-103,
0x1.a800p-108,
0x1.4c00p-106,
-0x1.9500p-106,
0x1.6900p-105,
-0x1.29d0p-100,
0x1.4c60p-103,
0x1.13a0p-102,
-0x1.5b60p-103,
-0x1.1c40p-103,
0x1.db80p-102,
0x1.91a0p-102,
0x1.dc00p-105,
0x1.44c0p-104,
0x1.9710p-102,
0x1.8760p-103,
-0x1.a720p-103,
0x1.ed20p-103,
-0x1.49c0p-102,
-0x1.e000p-111,
0x1.86a0p-103,
0x1.2b40p-103,
-0x1.b400p-108,
0x1.1280p-99,
-0x1.02d8p-102,
-0x1.e3d0p-103,
-0x1.b080p-105,
-0x1.f100p-107,
-0x1.16c0p-105,
-0x1.1190p-103,
-0x1.a7d2p-100,
0x1.3450p-103,
-0x1.67c0p-105,
0x1.4b80p-104,
-0x1.c4e0p-103,
0x1.6000p-108,
-0x1.3f60p-105,
0x1.93f0p-104,
0x1.5fe0p-105,
0x1.6f80p-107,
-0x1.7600p-106,
0x1.21e0p-106,
-0x1.3a40p-106,
-0x1.40c0p-104,
-0x1.9860p-105,
-0x1.5d40p-108,
-0x1.1d70p-106,
0x1.2760p-105,
0x0.0000p+0,
0x1.21e2p-104,
-0x1.9520p-108,
-0x1.5720p-106,
-0x1.4810p-106,
-0x1.be00p-109,
0x1.0080p-105,
-0x1.5780p-108,
-0x1.d460p-105,
-0x1.6140p-105,
0x1.4630p-104,
0x1.ad50p-103,
0x1.82e0p-105,
0x1.1d3cp-101,
0x1.6100p-107,
0x1.ec30p-104,
0x1.f200p-108,
0x1.0b40p-103,
0x1.3660p-102,
0x1.d9d0p-103,
-0x1.02d0p-102,
0x1.b070p-103,
0x1.b9c0p-104,
-0x1.01c0p-103,
-0x1.dfe0p-103,
0x1.1b60p-104,
-0x1.ae94p-101,
-0x1.3340p-104,
0x1.b3d8p-102,
-0x1.6e40p-105,
-0x1.3670p-103,
0x1.c140p-104,
0x1.1840p-101,
0x1.1ab0p-102,
-0x1.a400p-104,
0x1.1f00p-104,
-0x1.7180p-103,
0x1.4ce0p-102,
0x1.9200p-107,
-0x1.54c0p-103,
0x1.1b80p-105,
-0x1.1828p-101,
0x1.5720p-102,
-0x1.a060p-100,
0x1.9160p-102,
0x1.a280p-104,
0x1.3400p-107,
0x1.2b20p-102,
0x1.7800p-108,
0x1.cfd0p-101,
0x1.2ef0p-102,
-0x1.2760p-99,
0x1.b380p-104,
0x1.0048p-101,
-0x1.60b0p-102,
0x1.a1ccp-100,
-0x1.a640p-104,
-0x1.08a0p-101,
0x1.7e60p-102,
0x1.22c0p-103,
-0x1.7200p-106,
0x1.f0f0p-102,
0x1.eb4ep-99,
0x1.c6e0p-103,
};
/*
* exp2l(x): compute the base 2 exponential of x
*
* Accuracy: Peak error < 0.502 ulp.
*
* Method: (accurate tables)
*
* Reduce x:
* x = 2**k + y, for integer k and |y| <= 1/2.
* Thus we have exp2(x) = 2**k * exp2(y).
*
* Reduce y:
* y = i/TBLSIZE + z - eps[i] for integer i near y * TBLSIZE.
* Thus we have exp2(y) = exp2(i/TBLSIZE) * exp2(z - eps[i]),
* with |z - eps[i]| <= 2**-8 + 2**-98 for the table used.
*
* We compute exp2(i/TBLSIZE) via table lookup and exp2(z - eps[i]) via
* a degree-10 minimax polynomial with maximum error under 2**-120.
* The values in exp2t[] and eps[] are chosen such that
* exp2t[i] = exp2(i/TBLSIZE + eps[i]), and eps[i] is a small offset such
* that exp2t[i] is accurate to 2**-122.
*
* Note that the range of i is +-TBLSIZE/2, so we actually index the tables
* by i0 = i + TBLSIZE/2.
*
* This method is due to Gal, with many details due to Gal and Bachelis:
*
* Gal, S. and Bachelis, B. An Accurate Elementary Mathematical Library
* for the IEEE Floating Point Standard. TOMS 17(1), 26-46 (1991).
*/
long double
exp2l(long double x)
{
Use a better method of scaling by 2**k. Instead of adding to the exponent bits of the reduced result, construct 2**k (hopefully in parallel with the construction of the reduced result) and multiply by it. This tends to be much faster if the construction of 2**k is actually in parallel, and might be faster even with no parallelism since adjustment of the exponent requires a read-modify-wrtite at an unfortunate time for pipelines. In some cases involving exp2* on amd64 (A64), this change saves about 40 cycles or 30%. I think it is inherently only about 12 cycles faster in these cases and the rest of the speedup is from partly-accidentally avoiding compiler pessimizations (the construction of 2**k is now manually scheduled for good results, and -O2 doesn't always mess this up). In most cases on amd64 (A64) and i386 (A64) the speedup is about 20 cycles. The worst case that I found is expf on ia64 where this change is a pessimization of about 10 cycles or 5%. The manual scheduling for plain exp[f] is harder and not as tuned. This change ld128/s_exp2l.c has not been tested.
2008-02-07 03:17:05 +00:00
union IEEEl2bits u, v;
long double r, t, twopk, twopkp10000, z;
Implement exp2l(). There is one version for machines with 80-bit long doubles (i386, amd64, ia64) and one for machines with 128-bit long doubles (sparc64). Other platforms use the double version. I've only done runtime testing on i386. Thanks to bde@ for helpful discussions and bugfixes.
2008-01-18 21:42:46 +00:00
uint32_t hx, ix, i0;
int k;
u.e = x;
/* Filter out exceptional cases. */
hx = u.xbits.expsign;
ix = hx & EXPMASK;
if (ix >= BIAS + 14) { /* |x| >= 16384 */
if (ix == BIAS + LDBL_MAX_EXP) {
if (u.xbits.manh != 0
|| u.xbits.manl != 0
|| (hx & 0x8000) == 0)
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
return (x + x); /* x is NaN or +Inf */
Implement exp2l(). There is one version for machines with 80-bit long doubles (i386, amd64, ia64) and one for machines with 128-bit long doubles (sparc64). Other platforms use the double version. I've only done runtime testing on i386. Thanks to bde@ for helpful discussions and bugfixes.
2008-01-18 21:42:46 +00:00
else
return (0.0); /* x is -Inf */
}
if (x >= 16384)
return (huge * huge); /* overflow */
if (x <= -16495)
return (twom10000 * twom10000); /* underflow */
} else if (ix <= BIAS - 115) { /* |x| < 0x1p-115 */
return (1.0 + x);
}
/*
* 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 & 0xffffffff) + TBLSIZE / 2;
k = (int)i0 >> TBLBITS;
i0 = i0 & (TBLSIZE - 1);
u.e -= redux;
z = x - u.e;
Use a better method of scaling by 2**k. Instead of adding to the exponent bits of the reduced result, construct 2**k (hopefully in parallel with the construction of the reduced result) and multiply by it. This tends to be much faster if the construction of 2**k is actually in parallel, and might be faster even with no parallelism since adjustment of the exponent requires a read-modify-wrtite at an unfortunate time for pipelines. In some cases involving exp2* on amd64 (A64), this change saves about 40 cycles or 30%. I think it is inherently only about 12 cycles faster in these cases and the rest of the speedup is from partly-accidentally avoiding compiler pessimizations (the construction of 2**k is now manually scheduled for good results, and -O2 doesn't always mess this up). In most cases on amd64 (A64) and i386 (A64) the speedup is about 20 cycles. The worst case that I found is expf on ia64 where this change is a pessimization of about 10 cycles or 5%. The manual scheduling for plain exp[f] is harder and not as tuned. This change ld128/s_exp2l.c has not been tested.
2008-02-07 03:17:05 +00:00
v.xbits.manh = 0;
v.xbits.manl = 0;
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;
}
Implement exp2l(). There is one version for machines with 80-bit long doubles (i386, amd64, ia64) and one for machines with 128-bit long doubles (sparc64). Other platforms use the double version. I've only done runtime testing on i386. Thanks to bde@ for helpful discussions and bugfixes.
2008-01-18 21:42:46 +00:00
/* Compute r = exp2(y) = exp2t[i0] * p(z - eps[i]). */
t = tbl[i0]; /* exp2t[i0] */
z -= eps[i0]; /* eps[i0] */
r = t + t * z * (P1 + z * (P2 + z * (P3 + z * (P4 + z * (P5 + z * (P6
+ z * (P7 + z * (P8 + z * (P9 + z * P10)))))))));
/* Scale by 2**k. */
if(k >= LDBL_MIN_EXP) {
Use a better method of scaling by 2**k. Instead of adding to the exponent bits of the reduced result, construct 2**k (hopefully in parallel with the construction of the reduced result) and multiply by it. This tends to be much faster if the construction of 2**k is actually in parallel, and might be faster even with no parallelism since adjustment of the exponent requires a read-modify-wrtite at an unfortunate time for pipelines. In some cases involving exp2* on amd64 (A64), this change saves about 40 cycles or 30%. I think it is inherently only about 12 cycles faster in these cases and the rest of the speedup is from partly-accidentally avoiding compiler pessimizations (the construction of 2**k is now manually scheduled for good results, and -O2 doesn't always mess this up). In most cases on amd64 (A64) and i386 (A64) the speedup is about 20 cycles. The worst case that I found is expf on ia64 where this change is a pessimization of about 10 cycles or 5%. The manual scheduling for plain exp[f] is harder and not as tuned. This change ld128/s_exp2l.c has not been tested.
2008-02-07 03:17:05 +00:00
if (k == LDBL_MAX_EXP)
return (r * 2.0 * 0x1p16383L);
return (r * twopk);
Implement exp2l(). There is one version for machines with 80-bit long doubles (i386, amd64, ia64) and one for machines with 128-bit long doubles (sparc64). Other platforms use the double version. I've only done runtime testing on i386. Thanks to bde@ for helpful discussions and bugfixes.
2008-01-18 21:42:46 +00:00
} else {
Use a better method of scaling by 2**k. Instead of adding to the exponent bits of the reduced result, construct 2**k (hopefully in parallel with the construction of the reduced result) and multiply by it. This tends to be much faster if the construction of 2**k is actually in parallel, and might be faster even with no parallelism since adjustment of the exponent requires a read-modify-wrtite at an unfortunate time for pipelines. In some cases involving exp2* on amd64 (A64), this change saves about 40 cycles or 30%. I think it is inherently only about 12 cycles faster in these cases and the rest of the speedup is from partly-accidentally avoiding compiler pessimizations (the construction of 2**k is now manually scheduled for good results, and -O2 doesn't always mess this up). In most cases on amd64 (A64) and i386 (A64) the speedup is about 20 cycles. The worst case that I found is expf on ia64 where this change is a pessimization of about 10 cycles or 5%. The manual scheduling for plain exp[f] is harder and not as tuned. This change ld128/s_exp2l.c has not been tested.
2008-02-07 03:17:05 +00:00
return (r * twopkp10000 * twom10000);
Implement exp2l(). There is one version for machines with 80-bit long doubles (i386, amd64, ia64) and one for machines with 128-bit long doubles (sparc64). Other platforms use the double version. I've only done runtime testing on i386. Thanks to bde@ for helpful discussions and bugfixes.
2008-01-18 21:42:46 +00:00
}
}
Reference in New Issue Copy Permalink