https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80432
Bug ID: 80432
Summary: std::pow gives wrong results for long double arguments
Product: gcc
Version: 7.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: theivorytower at gmail dot com
Target Milestone: ---
With the latest gcc 7.0.1, whenever I pass long double arguments to std::pow,
the results are either nan or inf for most of the times. For example, the
following simple code outputs -nan while the expected result is 2:
#include <cmath>
#include <iostream>
int main() {
long double a = 4;
long double b = 0.5;
std::cout << std::pow(a, b) << std::endl;
}
If I set = 0.007 and b = 0.2, the output is inf while the expected result is
0.370697. The program behaves as expected if the arguments are double instead
of long double. The following is my gcc version info:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/7.0.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /home/hao/installers/aur-gcc-git/src/gcc/configure
--prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,lto --enable-shared --enable-threads=posix
--enable-libmpx --with-system-zlib --with-isl --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch
--disable-libssp --enable-gnu-unique-object --enable-linker-build-id
--enable-lto --enable-plugin --enable-install-libiberty
--with-linker-hash-style=gnu --enable-gnu-indirect-function --disable-multilib
--disable-werror --enable-checking=release
Thread model: posix
gcc version 7.0.1 20170413 (experimental) (GCC)
