From patchwork Tue Mar 20 23:01:56 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Patrick McGehearty X-Patchwork-Id: 26393 Received: (qmail 50826 invoked by alias); 20 Mar 2018 23:02:07 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 50358 invoked by uid 89); 20 Mar 2018 23:02:06 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-26.4 required=5.0 tests=BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, KAM_NUMSUBJECT, KAM_SHORT, SPF_PASS, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=ham version=3.3.2 spammy=eps, sk:patrick, 20m, SECTION X-HELO: aserp2120.oracle.com From: Patrick McGehearty To: libc-alpha@sourceware.org Subject: [PATCH] Improves __ieee754_exp(x) performance by 18-37% when |x| < 1.0397 Date: Tue, 20 Mar 2018 19:01:56 -0400 Message-Id: <1521586916-49507-1-git-send-email-patrick.mcgehearty@oracle.com> X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8838 signatures=668695 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=4 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=836 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1803200127 Adds a fast path to e_exp.c when |x| < 1.03972053527832. When values are tested in isolation, reduction in execution time is: aarch 30%, sparc 18%, x86 37%. When comparing benchtests/bench.out which includes values outside that range, the gains are: aarch 8%, sparc 5%, x86 9%. make check is clean (no increase in ulp for any math test). Testing 20M values for each rounding mode in that range shows approximately one in 200 values is off by 1 ulp. No value tested for exp(x) changed by 2 or more ulp. No observed change in performance or accuracy for x outside fast path range. These changes will be active for all platforms that don't provide their own exp() routines. They will also be active for ieee754 versions of ccos, ccosh, cosh, csin, csinh, sinh, exp10, gamma, and erf. ChangeLog: 2018-03-20 Patrick McGehearty * sysdeps/ieee754/dbl-64/e_exp.c: faster __ieee754_exp() * sysdeps/ieee754/dbl-64/eexp.tbl: New file for e_exp.c --- sysdeps/ieee754/dbl-64/e_exp.c | 48 +++++++++-- sysdeps/ieee754/dbl-64/eexp.tbl | 172 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 212 insertions(+), 8 deletions(-) create mode 100644 sysdeps/ieee754/dbl-64/eexp.tbl diff --git a/sysdeps/ieee754/dbl-64/e_exp.c b/sysdeps/ieee754/dbl-64/e_exp.c index 62035a8..e47b8af 100644 --- a/sysdeps/ieee754/dbl-64/e_exp.c +++ b/sysdeps/ieee754/dbl-64/e_exp.c @@ -40,6 +40,7 @@ #include #include #include +#include "eexp.tbl" #ifndef SECTION # define SECTION @@ -50,8 +51,10 @@ SECTION __ieee754_exp (double x) { double bexp, t, eps, del, base, y, al, bet, res, rem, cor; + double z; mynumber junk1, junk2, binexp = {{0, 0}}; int4 i, j, m, n, ex; + int4 k; double retval; { @@ -61,7 +64,42 @@ __ieee754_exp (double x) m = junk1.i[HIGH_HALF]; n = m & hugeint; - if (n > smallint && n < bigint) + if (n < 0x3ff0a2b2) /* |x| < 1.03972053527832 */ + { + if (n < 0x3f862e42) /* |x| < 3/2 ln 2 */ + { + if (n < 0x3ed00000) /* |x| < 1/64 ln 2 */ + { + if (n < 0x3e300000) /* |x| < 2^18 */ + { + retval = one + junk1.x; + goto ret; + } + retval = one + junk1.x * (one + half * junk1.x); + goto ret; + } + t = junk1.x * junk1.x; + retval = junk1.x + (t * (half + junk1.x * t2) + + (t * t) * (t3 + junk1.x * t4 + t * t5)); + retval = one + retval; + goto ret; + } + + /* Find the multiple of 2^-6 nearest x. */ + k = n >> 20; + j = (0x00100000 | (n & 0x000fffff)) >> (0x40c - k); + j = (j - 1) & ~1; + if (m < 0) + j += 134; + z = junk1.x - TBL2[j]; + t = z * z; + retval = z + (t * (half + (z * t2)) + + (t * t) * (t3 + z * t4 + t * t5)); + retval = TBL2[j + 1] + TBL2[j + 1] * retval; + goto ret; + } + + if (n < bigint) /* && |x| >= 1.03972053527832 */ { y = x * log2e.x + three51.x; bexp = y - three51.x; /* multiply the result by 2**bexp */ @@ -74,7 +112,7 @@ __ieee754_exp (double x) y = t + three33.x; base = y - three33.x; /* t rounded to a multiple of 2**-18 */ junk2.x = y; - del = (t - base) - eps; /* x = bexp*ln(2) + base + del */ + del = (t - base) - eps; /* x = bexp*ln(2) + base + del */ eps = del + del * del * (p3.x * del + p2.x); binexp.i[HIGH_HALF] = (junk1.i[LOW_HALF] + 1023) << 20; @@ -94,12 +132,6 @@ __ieee754_exp (double x) goto ret; } - if (n <= smallint) - { - retval = 1.0; - goto ret; - } - if (n >= badint) { if (n > infint) diff --git a/sysdeps/ieee754/dbl-64/eexp.tbl b/sysdeps/ieee754/dbl-64/eexp.tbl new file mode 100644 index 0000000..3b5fe40 --- /dev/null +++ b/sysdeps/ieee754/dbl-64/eexp.tbl @@ -0,0 +1,172 @@ +/* EXP function tables - for use in computing double precision exponential + Copyright (C) 2017 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +/* For i = 0, ..., 66, + TBL2[2*i] is a double precision number near (i+1)*2^-6, and + TBL2[2*i+1] = exp(TBL2[2*i]) to within a relative error less + than 2^-60. + + For i = 67, ..., 133, + TBL2[2*i] is a double precision number near -(i+1)*2^-6, and + TBL2[2*i+1] = exp(TBL2[2*i]) to within a relative error less + than 2^-60. */ + +static const double TBL2[268] = { + 0x1.ffffffffffc82p-7, 0x1.04080ab55de32p+0, + 0x1.fffffffffffdbp-6, 0x1.08205601127ecp+0, + 0x1.80000000000a0p-5, 0x1.0c49236829e91p+0, + 0x1.fffffffffff79p-5, 0x1.1082b577d34e9p+0, + 0x1.3fffffffffffcp-4, 0x1.14cd4fc989cd6p+0, + 0x1.8000000000060p-4, 0x1.192937074e0d4p+0, + 0x1.c000000000061p-4, 0x1.1d96b0eff0e80p+0, + 0x1.fffffffffffd6p-4, 0x1.2216045b6f5cap+0, + 0x1.1ffffffffff58p-3, 0x1.26a7793f6014cp+0, + 0x1.3ffffffffff75p-3, 0x1.2b4b58b372c65p+0, + 0x1.5ffffffffff00p-3, 0x1.3001ecf601ad1p+0, + 0x1.8000000000020p-3, 0x1.34cb8170b583ap+0, + 0x1.9ffffffffa629p-3, 0x1.39a862bd3b344p+0, + 0x1.c00000000000fp-3, 0x1.3e98deaa11dcep+0, + 0x1.e00000000007fp-3, 0x1.439d443f5f16dp+0, + 0x1.0000000000072p-2, 0x1.48b5e3c3e81abp+0, + 0x1.0fffffffffecap-2, 0x1.4de30ec211dfbp+0, + 0x1.1ffffffffff8fp-2, 0x1.5325180cfacd2p+0, + 0x1.300000000003bp-2, 0x1.587c53c5a7b04p+0, + 0x1.4000000000034p-2, 0x1.5de9176046007p+0, + 0x1.4ffffffffff89p-2, 0x1.636bb9a98322fp+0, + 0x1.5ffffffffffe7p-2, 0x1.690492cbf942ap+0, + 0x1.6ffffffffff78p-2, 0x1.6eb3fc55b1e45p+0, + 0x1.7ffffffffff65p-2, 0x1.747a513dbef32p+0, + 0x1.8ffffffffffd5p-2, 0x1.7a57ede9ea22ep+0, + 0x1.9ffffffffff6ep-2, 0x1.804d30347b50fp+0, + 0x1.affffffffffc3p-2, 0x1.865a7772164aep+0, + 0x1.c000000000053p-2, 0x1.8c802477b0030p+0, + 0x1.d00000000004dp-2, 0x1.92be99a09bf1ep+0, + 0x1.e000000000096p-2, 0x1.99163ad4b1e08p+0, + 0x1.efffffffffefap-2, 0x1.9f876d8e8c4fcp+0, + 0x1.fffffffffffd0p-2, 0x1.a61298e1e0688p+0, + 0x1.0800000000002p-1, 0x1.acb82581eee56p+0, + 0x1.100000000001fp-1, 0x1.b3787dc80f979p+0, + 0x1.17ffffffffff8p-1, 0x1.ba540dba56e4fp+0, + 0x1.1fffffffffffap-1, 0x1.c14b431256441p+0, + 0x1.27fffffffffc4p-1, 0x1.c85e8d43f7c9bp+0, + 0x1.2fffffffffffdp-1, 0x1.cf8e5d84758a6p+0, + 0x1.380000000001fp-1, 0x1.d6db26d16cd84p+0, + 0x1.3ffffffffffd8p-1, 0x1.de455df80e39bp+0, + 0x1.4800000000052p-1, 0x1.e5cd799c6a59cp+0, + 0x1.4ffffffffffc8p-1, 0x1.ed73f240dc10cp+0, + 0x1.5800000000013p-1, 0x1.f539424d90f71p+0, + 0x1.5ffffffffffbcp-1, 0x1.fd1de6182f885p+0, + 0x1.680000000002dp-1, 0x1.02912df5ce741p+1, + 0x1.7000000000040p-1, 0x1.06a39207f0a2ap+1, + 0x1.780000000004fp-1, 0x1.0ac660691652ap+1, + 0x1.7ffffffffff6fp-1, 0x1.0ef9db467dcabp+1, + 0x1.87fffffffffe5p-1, 0x1.133e45d82e943p+1, + 0x1.9000000000035p-1, 0x1.1793e4652cc6dp+1, + 0x1.97fffffffffb3p-1, 0x1.1bfafc47bda48p+1, + 0x1.a000000000000p-1, 0x1.2073d3f1bd518p+1, + 0x1.a80000000004ap-1, 0x1.24feb2f105ce2p+1, + 0x1.affffffffffedp-1, 0x1.299be1f3e7f11p+1, + 0x1.b7ffffffffffbp-1, 0x1.2e4baacdb6611p+1, + 0x1.c00000000001dp-1, 0x1.330e587b62b39p+1, + 0x1.c800000000079p-1, 0x1.37e437282d538p+1, + 0x1.cffffffffff51p-1, 0x1.3ccd943268248p+1, + 0x1.d7fffffffff74p-1, 0x1.41cabe304cadcp+1, + 0x1.e000000000011p-1, 0x1.46dc04f4e5343p+1, + 0x1.e80000000001ep-1, 0x1.4c01b9950a124p+1, + 0x1.effffffffff9ep-1, 0x1.513c2e6c73196p+1, + 0x1.f7fffffffffedp-1, 0x1.568bb722dd586p+1, + 0x1.0000000000034p+0, 0x1.5bf0a8b1457b0p+1, + 0x1.03fffffffffe2p+0, 0x1.616b5967376dfp+1, + 0x1.07fffffffff4bp+0, 0x1.66fc20f0337a9p+1, + 0x1.0bffffffffffdp+0, 0x1.6ca35859290f5p+1, + -0x1.fffffffffffe4p-7, 0x1.f80feabfeefa5p-1, + -0x1.ffffffffffb0bp-6, 0x1.f03f56a88b5fep-1, + -0x1.7ffffffffffa7p-5, 0x1.e88dc6afecfc5p-1, + -0x1.ffffffffffea8p-5, 0x1.e0fabfbc702b8p-1, + -0x1.3ffffffffffb3p-4, 0x1.d985c89d041acp-1, + -0x1.7ffffffffffe3p-4, 0x1.d22e6a0197c06p-1, + -0x1.bffffffffff9ap-4, 0x1.caf42e73a4c89p-1, + -0x1.fffffffffff98p-4, 0x1.c3d6a24ed822dp-1, + -0x1.1ffffffffffe9p-3, 0x1.bcd553b9d7b67p-1, + -0x1.3ffffffffffe0p-3, 0x1.b5efd29f24c2dp-1, + -0x1.5fffffffff553p-3, 0x1.af25b0a61a9f4p-1, + -0x1.7ffffffffff8bp-3, 0x1.a876812c08794p-1, + -0x1.9fffffffffe51p-3, 0x1.a1e1d93d68828p-1, + -0x1.bffffffffff6ep-3, 0x1.9b674f8f2f3f5p-1, + -0x1.dffffffffff7fp-3, 0x1.95067c7837a0cp-1, + -0x1.fffffffffff7ap-3, 0x1.8ebef9eac8225p-1, + -0x1.0fffffffffffep-2, 0x1.8890636e31f55p-1, + -0x1.1ffffffffff41p-2, 0x1.827a56188975ep-1, + -0x1.2ffffffffffbap-2, 0x1.7c7c708877656p-1, + -0x1.3fffffffffff8p-2, 0x1.769652df22f81p-1, + -0x1.4ffffffffff90p-2, 0x1.70c79eba33c2fp-1, + -0x1.5ffffffffffdbp-2, 0x1.6b0ff72deb8aap-1, + -0x1.6ffffffffff9ap-2, 0x1.656f00bf5798ep-1, + -0x1.7ffffffffff9fp-2, 0x1.5fe4615e98eb0p-1, + -0x1.8ffffffffffeep-2, 0x1.5a6fc061433cep-1, + -0x1.9fffffffffc4ap-2, 0x1.5510c67cd26cdp-1, + -0x1.affffffffff30p-2, 0x1.4fc71dc13566bp-1, + -0x1.bfffffffffff0p-2, 0x1.4a9271936fd0ep-1, + -0x1.cfffffffffff3p-2, 0x1.45726ea84fb8cp-1, + -0x1.dfffffffffff3p-2, 0x1.4066c2ff3912bp-1, + -0x1.effffffffff80p-2, 0x1.3b6f1ddd05ab9p-1, + -0x1.fffffffffffdfp-2, 0x1.368b2fc6f9614p-1, + -0x1.0800000000000p-1, 0x1.31baaa7dca843p-1, + -0x1.0ffffffffffa4p-1, 0x1.2cfd40f8bdce4p-1, + -0x1.17fffffffff0ap-1, 0x1.2852a760d5ce7p-1, + -0x1.2000000000000p-1, 0x1.23ba930c1568bp-1, + -0x1.27fffffffffbbp-1, 0x1.1f34ba78d568dp-1, + -0x1.2fffffffffe32p-1, 0x1.1ac0d5492c1dbp-1, + -0x1.37ffffffff042p-1, 0x1.165e9c3e67ef2p-1, + -0x1.3ffffffffff77p-1, 0x1.120dc93499431p-1, + -0x1.47fffffffff6bp-1, 0x1.0dce171e34ecep-1, + -0x1.4fffffffffff1p-1, 0x1.099f41ffbe588p-1, + -0x1.57ffffffffe02p-1, 0x1.058106eb8a7aep-1, + -0x1.5ffffffffffe5p-1, 0x1.017323fd9002ep-1, + -0x1.67fffffffffb0p-1, 0x1.faeab0ae9386cp-2, + -0x1.6ffffffffffb2p-1, 0x1.f30ec837503d7p-2, + -0x1.77fffffffff7fp-1, 0x1.eb5210d627133p-2, + -0x1.7ffffffffffe8p-1, 0x1.e3b40ebefcd95p-2, + -0x1.87fffffffffc8p-1, 0x1.dc3448110dae2p-2, + -0x1.8fffffffffb30p-1, 0x1.d4d244cf4ef06p-2, + -0x1.97fffffffffefp-1, 0x1.cd8d8ed8ee395p-2, + -0x1.9ffffffffffa7p-1, 0x1.c665b1e1f1e5cp-2, + -0x1.a7fffffffffdcp-1, 0x1.bf5a3b6bf18d6p-2, + -0x1.affffffffff95p-1, 0x1.b86ababeef93bp-2, + -0x1.b7fffffffffcbp-1, 0x1.b196c0e24d256p-2, + -0x1.bffffffffff32p-1, 0x1.aadde095dadf7p-2, + -0x1.c7fffffffff6ap-1, 0x1.a43fae4b047c9p-2, + -0x1.cffffffffffb6p-1, 0x1.9dbbc01e182a4p-2, + -0x1.d7fffffffffcap-1, 0x1.9751adcfa81ecp-2, + -0x1.dffffffffffcdp-1, 0x1.910110be0699ep-2, + -0x1.e7ffffffffffbp-1, 0x1.8ac983dedbc69p-2, + -0x1.effffffffff88p-1, 0x1.84aaa3b8d51a9p-2, + -0x1.f7fffffffffbbp-1, 0x1.7ea40e5d6d92ep-2, + -0x1.fffffffffffdbp-1, 0x1.78b56362cef53p-2, + -0x1.03fffffffff00p+0, 0x1.72de43ddcb1f2p-2, + -0x1.07ffffffffe6fp+0, 0x1.6d1e525bed085p-2, + -0x1.0bfffffffffd6p+0, 0x1.677532dda1c57p-2}; + +static const double + half = 0.5, + one = 1.0, +/* t2-t5 terms used for polynomial computation. */ + t2 = 0x1.5555555555555p-3, /* 1.6666666666666665741e-1 */ + t3 = 0x1.5555555555555p-5, /* 4.1666666666666664354e-2 */ + t4 = 0x1.1111111111111p-7, /* 8.3333333333333332177e-3 */ + t5 = 0x1.6c16c16c16c17p-10; /* 1.3888888888888889419e-3 */