Lasse Kliemann wrote: > Greetings, > > I have a C++ program that does some linear programming optimization. Out of > this linear programming, I get a vector of doubles `x' and a double `opt' > that should be the sum of the entries in `x' (`x' is the solution vector and > `opt' is the optimal value). As a consistency chek, I compute the sum of the > elements of `x' and then compute the difference to `opt'. It should be close > to zero. Here is a snippet from the code: > > double sum = 0; > const double *x = model->getColSolution(); > for (unsigned int j=0; j<m; ++j) sum += x[j]; > double d=opt-sum; > cout << "difference: " << d << endl; > > If I compile that with g++ version 4.3.0 and -O0, -O1, or -Os, everything > looks OK; in rare cases the difference is zero, and in most cases it is a > very small number. Now, if I compile that with -O2 or -O3, the difference is > *always* printed to be zero, which I presume is wrong. http://gcc.gnu.org/bugzilla/show_bug.cgi?id=323\
