https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89979
Bug ID: 89979 Summary: subtract_with_carry_engine incorrect carry flag Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: g...@christoph-conrads.name Target Milestone: --- Created attachment 46090 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46090&action=edit The initial state in combination with the incorrect carry computation makes the PRNG enter the unescapable all zero state. The carry inside `std::subtract_with_carry_engine` is computed incorrectly if word_size == std::numeric_limits<result_type>::digits. The bug can be triggered neither by std::ranlux24 nor by std::ranlux48. The bug occurs with GCC 7.3.0, GCC 8.2.0, and Clang when using the GNU Standard C++ Library shipping with GCC 7.3.0. $ gcc --version gcc (Gentoo 7.3.0-r3 p1.4) 7.3.0 Copyright (C) 2017 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. $ g++-7.3.0 -Wextra -Wall -std=c++11 -pedantic -v -save-temps ~/libstdcxx-swc-bug.cpp Using built-in specs. COLLECT_GCC=g++-7.3.0 COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /var/tmp/portage/sys-devel/gcc-7.3.0-r3/work/gcc-7.3.0/configure --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/7.3.0 --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/7.3.0 --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/7.3.0/man --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/7.3.0/info --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include/g++-v7 --with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/7.3.0/python --enable-languages=c,c++,fortran --enable-obsolete --enable-secureplt --disable-werror --with-system-zlib --enable-nls --without-included-gettext --enable-checking=release --with-bugurl=https://bugs.gentoo.org/ --with-pkgversion='Gentoo 7.3.0-r3 p1.4' --disable-esp --enable-libstdcxx-time --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --disable-multilib --with-multilib-list=m64 --disable-altivec --disable-fixed-point --enable-targets=all --enable-libgomp --disable-libmudflap --disable-libssp --disable-libcilkrts --disable-libmpx --enable-vtable-verify --enable-libvtv --enable-lto --without-isl --enable-libsanitizer --enable-default-pie --enable-default-ssp Thread model: posix gcc version 7.3.0 (Gentoo 7.3.0-r3 p1.4) COLLECT_GCC_OPTIONS='-Wextra' '-Wall' '-std=c++11' '-Wpedantic' '-v' '-save-temps' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/cc1plus -E -quiet -v -D_GNU_SOURCE /home/starfish/libstdcxx-swc-bug.cpp -mtune=generic -march=x86-64 -std=c++11 -Wextra -Wall -Wpedantic -fpch-preprocess -o libstdcxx-swc-bug.ii ignoring nonexistent directory "/usr/local/include" ignoring nonexistent directory "/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../x86_64-pc-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include/g++-v7 /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include/g++-v7/x86_64-pc-linux-gnu /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include/g++-v7/backward /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include-fixed /usr/include End of search list. COLLECT_GCC_OPTIONS='-Wextra' '-Wall' '-std=c++11' '-Wpedantic' '-v' '-save-temps' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/cc1plus -fpreprocessed libstdcxx-swc-bug.ii -quiet -dumpbase libstdcxx-swc-bug.cpp -mtune=generic -march=x86-64 -auxbase libstdcxx-swc-bug -Wextra -Wall -Wpedantic -std=c++11 -version -o libstdcxx-swc-bug.s GNU C++11 (Gentoo 7.3.0-r3 p1.4) version 7.3.0 (x86_64-pc-linux-gnu) compiled by GNU C version 7.3.0, GMP version 6.1.2, MPFR version 3.1.6, MPC version 1.0.3, isl version none GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 GNU C++11 (Gentoo 7.3.0-r3 p1.4) version 7.3.0 (x86_64-pc-linux-gnu) compiled by GNU C version 7.3.0, GMP version 6.1.2, MPFR version 3.1.6, MPC version 1.0.3, isl version none GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: 09ac773f85349e020b5b36ead38f9924 COLLECT_GCC_OPTIONS='-Wextra' '-Wall' '-std=c++11' '-Wpedantic' '-v' '-save-temps' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../x86_64-pc-linux-gnu/bin/as -v --64 -o libstdcxx-swc-bug.o libstdcxx-swc-bug.s GNU assembler version 2.30.0 (x86_64-pc-linux-gnu) using BFD version (Gentoo 2.30 p5) 2.30.0 COMPILER_PATH=/usr/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/:/usr/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/:/usr/libexec/gcc/x86_64-pc-linux-gnu/:/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/:/usr/lib/gcc/x86_64-pc-linux-gnu/:/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../x86_64-pc-linux-gnu/bin/ LIBRARY_PATH=/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/:/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../x86_64-pc-linux-gnu/lib/:/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-Wextra' '-Wall' '-std=c++11' '-Wpedantic' '-v' '-save-temps' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/collect2 -plugin /usr/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/liblto_plugin.so -plugin-opt=/usr/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/lto-wrapper -plugin-opt=-fresolution=libstdcxx-swc-bug.res -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -pie /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../lib64/Scrt1.o /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../lib64/crti.o /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/crtbeginS.o -L/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0 -L/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../x86_64-pc-linux-gnu/lib -L/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../.. libstdcxx-swc-bug.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/crtendS.o /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../lib64/crtn.o COLLECT_GCC_OPTIONS='-Wextra' '-Wall' '-std=c++11' '-Wpedantic' '-v' '-save-temps' '-shared-libgcc' '-mtune=generic' '-march=x86-64'