------- Comment #3 from christopher dot eltschka at physik dot uni-regensburg
dot de 2005-10-27 09:11 -------
I just stumbled on the same problem, but with much more conventional numbers.
The following C++ test program demonstrates it:
#include <iostream>
// this just serves to calculate a positive number which the optimizer
// will not figure out at compile time
long double f()
{
long double value = 1.0;
for (int i = 0; i < 10; ++i)
value += (long double)i;
return value;
}
int main()
{
long double a = f();
std::cout << a;
if (a > 0)
std::cout << " > 0\n";
else if (a < 0)
std::cout << " < 0\n";
else if (a == 0)
std::cout << " == 0\n";
else
std::cout << "oops!\n";
}
Compiling and running gives:
> g++ longdouble.cc -O3 && a.out
46 == 0
which is clearly wrong. The same result happens with -O2 and -O1. With -O0 I
correctly get the output 46 > 0.
The compiler is:
> g++ -v
Reading specs from /usr/local/lib/gcc-lib/alphaev67-dec-osf5.1/3.3/specs
Configured with: ../gcc-3.3/configure --with-libiconv-prefix=/usr/local
--with-included-gettext
Thread model: single
gcc version 3.3
As workaround for == 0, !! seems to work. Unfortunately I don't know a
workaround for > 0 and < 0.
--
christopher dot eltschka at physik dot uni-regensburg dot de changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |christopher dot eltschka at
| |physik dot uni-regensburg
| |dot de
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12639
