From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 48FD13858C27; Mon, 18 Oct 2021 23:54:35 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 48FD13858C27 From: "mwelinder at gmail dot com" To: glibc-bugs@sourceware.org Subject: [Bug math/28472] New: pow(10, i) accuracy Date: Mon, 18 Oct 2021 23:54:35 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: glibc X-Bugzilla-Component: math X-Bugzilla-Version: 2.31 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: mwelinder at gmail dot com X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Resolution: X-Bugzilla-Priority: P2 X-Bugzilla-Assigned-To: unassigned at sourceware dot org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status bug_severity priority component assigned_to reporter target_milestone attachments.created Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://sourceware.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: glibc-bugs@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Glibc-bugs mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 18 Oct 2021 23:54:35 -0000 https://sourceware.org/bugzilla/show_bug.cgi?id=3D28472 Bug ID: 28472 Summary: pow(10, i) accuracy Product: glibc Version: 2.31 Status: UNCONFIRMED Severity: normal Priority: P2 Component: math Assignee: unassigned at sourceware dot org Reporter: mwelinder at gmail dot com Target Milestone: --- Created attachment 13725 --> https://sourceware.org/bugzilla/attachment.cgi?id=3D13725&action=3Ded= it Test program When the attached test program is run, I see two cases where pow(10,i) disagrees with atof(1e$i") for an integer i. This is a last-bit rounding issue. The values returned by pow(10,i) are ve= ry close and normally I would cut pow a bit of slack -- it is a lot trickier t= han the single-argument functions like sin, cos, or exp. However, pow(10,i) is a fairly important case that it would make sense to handle accurately. $ ./a.out=20 i =3D 23 a =3D 100000000000000008388608 b =3D 99999999999999991611392 Midpoint i =3D 210 a =3D 100000000000000007311188218325485257111615953570420507004223762444111242223= 779285187536341014385741266761068799969763125334902791605243044670546908252= 8474390439305760542775847335624615778546587814778848485048320 b =3D 999999999999999927113782419344605574598668153294882673458925392487194643703= 632279098558059466181044478400725843812838336795121561031396504666917998514= 458446354143529431921823271795036250068185162804696593727488 b is best after 17 digits -------------------------------------------------- Note: On another machine I have seen a failure for i=3D216, but only in 32-= bit mode. There might be hardware dependencies here. $ grep Intel /proc/cpuinfo | head -2 vendor_id : GenuineIntel model name : Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz $ grep PRETTY /etc/os-release=20 PRETTY_NAME=3D"Linux Mint 20.2" I believe I am using libc version 2.31-0ubuntu9.2cross1 Compilation: $ gcc -v -g -Wall -O2 eee.c -lm Using built-in specs. COLLECT_GCC=3Dgcc COLLECT_LTO_WRAPPER=3D/usr/lib/gcc/x86_64-linux-gnu/9/lto-wrapper OFFLOAD_TARGET_NAMES=3Dnvptx-none:hsa OFFLOAD_TARGET_DEFAULT=3D1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion=3D'Ubuntu 9.3.0-17ubuntu1~20.04' --with-bugurl=3Dfile:///usr/share/doc/gcc-9/README.B= ugs --enable-languages=3Dc,ada,c++,go,brig,d,fortran,objc,obj-c++,gm2 --prefix= =3D/usr --with-gcc-major-version-only --program-suffix=3D-9 --program-prefix=3Dx86_64-linux-gnu- --enable-shared --enable-linker-build-= id --libexecdir=3D/usr/lib --without-included-gettext --enable-threads=3Dposix --libdir=3D/usr/lib --enable-nls --enable-clocale=3Dgnu --enable-libstdcxx-= debug --enable-libstdcxx-time=3Dyes --with-default-libstdcxx-abi=3Dnew --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib=3Dauto --enable-objc-gc=3Dauto --enable-multiarch --disable-werror --with-arch-32= =3Di686 --with-abi=3Dm64 --with-multilib-list=3Dm32,m64,mx32 --enable-multilib --with-tune=3Dgeneric --enable-offload-targets=3Dnvptx-none=3D/build/gcc-9-HskZEa/gcc-9-9.3.0/deb= ian/tmp-nvptx/usr,hsa --without-cuda-driver --enable-checking=3Drelease --build=3Dx86_64-linux-gnu --host=3Dx86_64-linux-gnu --target=3Dx86_64-linux-gnu Thread model: posix gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)=20 COLLECT_GCC_OPTIONS=3D'-v' '-g' '-Wall' '-O2' '-mtune=3Dgeneric' '-march=3D= x86-64' /usr/lib/gcc/x86_64-linux-gnu/9/cc1 -quiet -v -imultiarch x86_64-linux-gnu eee.c -quiet -dumpbase eee.c -mtune=3Dgeneric -march=3Dx86-64 -auxbase eee = -g -O2 -Wall -version -fasynchronous-unwind-tables -fstack-protector-strong -Wformat-security -fstack-clash-protection -fcf-protection -o /tmp/ccbP42NQ= .s GNU C17 (Ubuntu 9.3.0-17ubuntu1~20.04) version 9.3.0 (x86_64-linux-gnu) compiled by GNU C version 9.3.0, GMP version 6.2.0, MPFR version 4.= 0.2, MPC version 1.1.0, isl version isl-0.22.1-GMP GGC heuristics: --param ggc-min-expand=3D100 --param ggc-min-heapsize=3D131= 072 ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/9/include-fix= ed" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/9/../../../../x86_64-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /usr/lib/gcc/x86_64-linux-gnu/9/include /usr/local/include /usr/include/x86_64-linux-gnu /usr/include End of search list. GNU C17 (Ubuntu 9.3.0-17ubuntu1~20.04) version 9.3.0 (x86_64-linux-gnu) compiled by GNU C version 9.3.0, GMP version 6.2.0, MPFR version 4.= 0.2, MPC version 1.1.0, isl version isl-0.22.1-GMP GGC heuristics: --param ggc-min-expand=3D100 --param ggc-min-heapsize=3D131= 072 Compiler executable checksum: bbf13931d8de1abe14040c9909cb6969 COLLECT_GCC_OPTIONS=3D'-v' '-g' '-Wall' '-O2' '-mtune=3Dgeneric' '-march=3D= x86-64' as -v --64 -o /tmp/ccSWUKiU.o /tmp/ccbP42NQ.s GNU assembler version 2.34 (x86_64-linux-gnu) using BFD version (GNU Binuti= ls for Ubuntu) 2.34 COMPILER_PATH=3D/usr/lib/gcc/x86_64-linux-gnu/9/:/usr/lib/gcc/x86_64-linux-= gnu/9/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/9/:/usr= /lib/gcc/x86_64-linux-gnu/ LIBRARY_PATH=3D/usr/lib/gcc/x86_64-linux-gnu/9/:/usr/lib/gcc/x86_64-linux-g= nu/9/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/9/../../../..= /lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/l= ib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/9/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS=3D'-v' '-g' '-Wall' '-O2' '-mtune=3Dgeneric' '-march=3D= x86-64' /usr/lib/gcc/x86_64-linux-gnu/9/collect2 -plugin /usr/lib/gcc/x86_64-linux-gnu/9/liblto_plugin.so -plugin-opt=3D/usr/lib/gcc/x86_64-linux-gnu/9/lto-wrapper -plugin-opt=3D-fresolution=3D/tmp/ccMHqq8T.res -plugin-opt=3D-pass-through= =3D-lgcc -plugin-opt=3D-pass-through=3D-lgcc_s -plugin-opt=3D-pass-through=3D-lc -plugin-opt=3D-pass-through=3D-lgcc -plugin-opt=3D-pass-through=3D-lgcc_s -= -build-id --eh-frame-hdr -m elf_x86_64 --hash-style=3Dgnu --as-needed -dynamic-linker /lib64/ld-linux-x86-64.so.2 -pie -z now -z relro /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/Scrt1.o /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crti.o /usr/lib/gcc/x86_64-linux-gnu/9/crtbeginS.o -L/usr/lib/gcc/x86_64-linux-gnu= /9 -L/usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu -L/usr/lib/gcc/x86_64-linux-gnu/9/../../../../lib -L/lib/x86_64-linux-gnu -L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/9/../../.. /tmp/ccSWUKiU.o -lm -lgcc --push-state --as-needed -lgcc_s --pop-state -lc -lgcc --push-state --as-ne= eded -lgcc_s --pop-state /usr/lib/gcc/x86_64-linux-gnu/9/crtendS.o /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crtn.o COLLECT_GCC_OPTIONS=3D'-v' '-g' '-Wall' '-O2' '-mtune=3Dgeneric' '-march=3D= x86-64' --=20 You are receiving this mail because: You are on the CC list for the bug.=