https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67932
Bug ID: 67932
Summary: Incorrect conversion to hexfloat
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: rcopley at gmail dot com
Target Milestone: ---
Created attachment 36481
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36481&action=edit
Preprocessed source file that demonstrates incorrect conversion from
floating-point value to string in hexfloat format
In GCC 5.2, in C++11, converting a floating-point value to a string in
hexadecimal floating-point (hexfloat) format gives incorrect results. The same
incorrect results occur when using std::printf from <cstdio> or using the
iostreams manipulator std::hexfloat. Using printf from <stdio.h> gives the
correct results (even in C++).
Output of gcc -v:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=C:/mingw64/bin/../libexec/gcc/x86_64-w64-mingw32/5.2.0/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: ../../../src/gcc-5.2.0/configure --host=x86_64-w64-mingw32
--build=x86_64-w64-mingw32 --target=x86_64-w64-mingw32 --prefix=/mingw64
--with-sysroot=/c/mingw520/x86_64-520-posix-seh-rt_v4-rev0/mingw64
--with-gxx-include-dir=/mingw64/x86_64-w64-mingw32/include/c++ --enable-shared
--enable-static --disable-multilib
--enable-languages=c,c++,fortran,objc,obj-c++,lto --enable-libstdcxx-time=yes
--enable-threads=posix --enable-libgomp --enable-libatomic --enable-lto
--enable-graphite --enable-checking=release --enable-fully-dynamic-string
--enable-version-specific-runtime-libs --disable-isl-version-check
--disable-libstdcxx-pch --disable-libstdcxx-debug --enable-bootstrap
--disable-rpath --disable-win32-registry --disable-nls --disable-werror
--disable-symvers --with-gnu-as --with-gnu-ld --with-arch=nocona
--with-tune=core2 --with-libiconv --with-system-zlib
--with-gmp=/c/mingw520/prerequisites/x86_64-w64-mingw32-static
--with-mpfr=/c/mingw520/prerequisites/x86_64-w64-mingw32-static
--with-mpc=/c/mingw520/prerequisites/x86_64-w64-mingw32-static
--with-isl=/c/mingw520/prerequisites/x86_64-w64-mingw32-static
--with-pkgversion='x86_64-posix-seh-rev0, Built by MinGW-W64 project'
--with-bugurl=http://sourceforge.net/projects/mingw-w64 CFLAGS='-O2 -pipe
-I/c/mingw520/x86_64-520-posix-seh-rt_v4-rev0/mingw64/opt/include
-I/c/mingw520/prerequisites/x86_64-zlib-static/include
-I/c/mingw520/prerequisites/x86_64-w64-mingw32-static/include' CXXFLAGS='-O2
-pipe -I/c/mingw520/x86_64-520-posix-seh-rt_v4-rev0/mingw64/opt/include
-I/c/mingw520/prerequisites/x86_64-zlib-static/include
-I/c/mingw520/prerequisites/x86_64-w64-mingw32-static/include' CPPFLAGS=
LDFLAGS='-pipe -L/c/mingw520/x86_64-520-posix-seh-rt_v4-rev0/mingw64/opt/lib
-L/c/mingw520/prerequisites/x86_64-zlib-static/lib
-L/c/mingw520/prerequisites/x86_64-w64-mingw32-static/lib '
Thread model: posix
gcc version 5.2.0 (x86_64-posix-seh-rev0, Built by MinGW-W64 project)
Complete command line that triggers the bug:
g++ -save-temps -std=c++11 -o hexfloat-bug.exe hexfloat-bug.cpp &&
hexfloat-bug.exe
Compiler output: none.
Preprocessed source file: see attached.
Expected program output:
1.0000000000000002e+000 0x1.0000000000001p+0 0x1.000000p+0
1.0000000000000036e+000 0x1.0000000000010p+0 0x1.000000p+0
1.0000000000000568e+000 0x1.0000000000100p+0 0x1.000000p+0
1.0000000000009095e+000 0x1.0000000001000p+0 0x1.000000p+0
1.0000000000145519e+000 0x1.0000000010000p+0 0x1.000000p+0
1.0000000002328306e+000 0x1.0000000100000p+0 0x1.000000p+0
1.0000000037252903e+000 0x1.0000001000000p+0 0x1.000000p+0
1.0000000596046448e+000 0x1.0000010000000p+0 0x1.000001p+0
1.0000009536743164e+000 0x1.0000100000000p+0 0x1.000010p+0
1.0000152587890625e+000 0x1.0001000000000p+0 0x1.000100p+0
Actual program output:
1.0000000000000002e+000 0x8.0000000000000p-55 0x8p-55
1.0000000000000036e+000 0x8.0000000000000p-51 0x8p-51
1.0000000000000568e+000 0x8.0000000000000p-47 0x8p-47
1.0000000000009095e+000 0x8.0000000000000p-43 0x8p-43
1.0000000000145519e+000 0x8.0000000000000p-39 0x8p-39
1.0000000002328306e+000 0x8.0000000000000p-35 0x8p-35
1.0000000037252903e+000 0x8.0000008000000p-3 0x0p-63
1.0000000596046448e+000 0x8.0000080000000p-3 0x0p-63
1.0000009536743164e+000 0x0.0000000000000p-55 0x0p-63
1.0000152587890625e+000 0x0.0000000000000p-55 0x0p-63
