Andrew Haley wrote: > 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\ http://gcc.gnu.org/bugzilla/show_bug.cgi?id=323
