[Bug c++/17802] New: Equal double member function calls results in <= expression returning false

[jonathan at csse dot uwa dot edu dot au]

"a" and "b" are instances of a struct with identical values.  The struct has a 
member function named "toReal()" that returns a double value based on the 
result of a simple calculation.  "a.toReal() <= b.toReal()" returns false, 
which seems wrong.  If toReal() is redefined with a float return value, it 
returns true, as expected.  If I assign the results of the double toReal() 
calls to a pair of double variables and test the variables with <=, the 
problem goes away (workaround).  Stepping through the double version in gdb 
shows all the values to be as expected (identical), but the <= test fails.  
Evaluating "p a.toReal() <= b.toReal()" in gdb prints true. 
 
I'm using g++ 3.3.3 (SuSE GNU/Linux 9.1), but see the same behaviour on 3.4.2 
and 3.2.2 (Red Hat) as well. 
 
I've made the .ii and .s files available on the web at the URLs below, rather 
than including them here (they're long).  I've renamed the files to indicate 
whether they were compiled with double or float return values. 
 
http://www.csse.uwa.edu.au/~jonathan/t.cc 
http://www.csse.uwa.edu.au/~jonathan/t-double.ii 
http://www.csse.uwa.edu.au/~jonathan/t-double.s 
http://www.csse.uwa.edu.au/~jonathan/t-float.ii 
http://www.csse.uwa.edu.au/~jonathan/t-float.s 
 
[I've reordered the command sequence below for clarity] 
======== 
piehole[1021] g++ -v 
Reading specs from /usr/lib/gcc-lib/i586-suse-linux/3.3.3/specs 
Configured with: ../configure --enable-threads=posix --prefix=/usr 
--with-local-prefix=/usr/local --infodir=/usr/share/info 
--mandir=/usr/share/man --enable-languages=c,c++,f77,objc,java,ada 
--disable-checking --libdir=/usr/lib --enable-libgcj 
--with-gxx-include-dir=/usr/include/g++ --with-slibdir=/lib --with-system-zlib 
--enable-shared --enable-__cxa_atexit i586-suse-linux 
Thread model: posix 
gcc version 3.3.3 (SuSE Linux) 
======== 
piehole[1026] g++ -o t -save-temps t.cc 
piehole[1027] ./t 
Using double 
a < b false 
a <= b false 
ad < bd false 
ad <= bd true 
======== 
(edit t.cc changing "#if 1" to "#if 0") 
piehole[1038] g++ -o t -save-temps t.cc 
piehole[1039] ./t 
Using float 
a < b false 
a <= b true 
ad < bd false 
ad <= bd true 
======== 
piehole[1032] cat t.cc 
#include <sys/time.h> 
#include <iostream> 
 
using std::cout; 
 
 
#if 1 
 
typedef double RealType; 
const char* realTypeName = "double"; 
 
#else 
 
typedef float RealType; 
const char* realTypeName = "float"; 
 
#endif 
 
struct TimeVal : public timeval 
{ 
    TimeVal(RealType t) { 
        tv_sec = static_cast<unsigned int>(t); 
        tv_usec = static_cast<unsigned int>(1e6 * (t - tv_sec)); 
    } 
 
    RealType toReal() { return tv_sec + 1e-6 * tv_usec; } 
}; 
 
int 
main(int argc, 
     char** argv) 
{ 
    cout << "Using " << realTypeName << '\n'; 
 
    TimeVal a(2.1); 
    TimeVal b(2.1); 
 
    if (a.toReal() < b.toReal()) 
        cout << "a < b true\n"; 
    else 
        cout << "a < b false\n"; 
 
    if (a.toReal() <= b.toReal()) 
        cout << "a <= b true\n"; 
    else 
        cout << "a <= b false\n"; 
 
    RealType ad = a.toReal(); 
    RealType bd = b.toReal(); 
 
    if (ad < bd) 
        cout << "ad < bd true\n"; 
    else 
        cout << "ad < bd false\n"; 
 
    if (ad <= bd) 
        cout << "ad <= bd true\n"; 
    else 
        cout << "ad <= bd false\n"; 
}

-- 
           Summary: Equal double member function calls results in <=
                    expression returning false
           Product: gcc
           Version: 3.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jonathan at csse dot uwa dot edu dot au
                CC: gcc-bugs at gcc dot gnu dot org
  GCC host triplet: 3.3.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17802