Summary: | Comparisons of double values don't work correctly | ||
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Product: | gcc | Reporter: | W. Tasin <tasin> |
Component: | c++ | Assignee: | Not yet assigned to anyone <unassigned> |
Status: | RESOLVED DUPLICATE | ||
Severity: | normal | CC: | daniel.kruegler |
Priority: | P3 | Keywords: | build |
Version: | 4.7.2 | ||
Target Milestone: | --- | ||
Host: | Target: | ||
Build: | Known to work: | ||
Known to fail: | Last reconfirmed: | ||
Attachments: | example code (as .ii) |
Using gcc 4.8.0 20121209 (experimental) (also mingw, but 64-bit on Windows 7) returns "false" for me. Use -fexcess-precision=standard *** This bug has been marked as a duplicate of bug 323 *** If only ... cc1plus: sorry, unimplemented: -fexcess-precision=standard for C++ |
Created attachment 29027 [details] example code (as .ii) A simple comparison shows that floating point operations with the c++-type double doesn't set the floating status flag correctly. Changing the type of the members of the class Load to float or long double makes the application work correctly. In the attached example the free function bool operator<(const Load &, const Load &); doesn't work correctly. The example returns the output: Compare: true instead of Compare: false This example was compiled in different configurations and on different machines with the same wrong result: System configuration 1: --- Intel(R) Core(TM)2 CPU 6420 @ 2.13GHz 3 GB RAM (pae) Windows XP Professional Version 2002 SP3 32 bit arch --- Es werden eingebaute Spezifikationen verwendet. COLLECT_GCC=g++ COLLECT_LTO_WRAPPER=c:/mingw/bin/../libexec/gcc/mingw32/4.7.2/lto-wrapper.exe Ziel: mingw32 Konfiguriert mit: ../gcc-4.7.2/configure --enable-languages=c,c++,ada,fortran,objc,obj-c++ --disable-sjlj-exceptions --with-dwarf2 --enable-shared --enable-libgomp --disable-win32-registry --enable-libstdcxx-debug --disable-build-poststage1 -with-cxx --enable-version-specific-runtime-libs --build=mingw32 --prefix=/mingw Thread-Modell: win32 gcc-Version 4.7.2 (GCC) --- The build process call was: g++ -v -save-temps -Wall -pedantic -Wextra -o derror.exe src\derror.cpp --- derror.cpp --- // test routine to show the double error #include <iostream> #include <stdexcept> using namespace std; // class definition class Load { double m_dPowerOut, m_dEfficiency; public: Load(double powerOut, double eff=1) : m_dPowerOut(powerOut), m_dEfficiency(eff) { }; virtual double consumption() const; virtual ~Load() { } }; bool operator<(const Load &a, const Load &b); // class method definition double Load::consumption(void) const { if (m_dEfficiency==0.0) throw logic_error("Efficiency must not be 0"); return m_dPowerOut/m_dEfficiency; } /// free function // ... doesn't work correctly bool operator<(const Load &a, const Load &b) { return a.consumption() < b.consumption(); } /* // ... seems to work correctly, but the float-status-flag IMHO // still isn't correct bool operator<(const Load &a, const Load &b) { double bcon=b.consumption(); return a.consumption() < bcon; } */ int main() { try { Load pump(53.0, 0.43); bool cmp=(pump < pump); // should be false !!! cout << "Compare: " << (cmp ? "true" : "false") << endl; } catch (const exception &ex) { cerr << "Exception: " << ex.what() << endl; } return 0; }