On 12/08/11 06:27, Ian Lance Taylor wrote:
Torquil Macdonald Sørensen<torquil@xxxxxxxxx> writes:#include "iostream" #include "blitz/array.h" int main() { blitz::Array<double,1> X(3); X = 0.0; blitz::Array<double,1> var(1); var = 0.0; for(int i = 0; i != 1; ++i) { for(int c = 0; c != 3; ++c) X(c) = double(c); var(i) = 0.0; for(int c = 0; c != 3; ++c) var(i) += X(c)*X(c); var(i) /= 3.0; } std::cout<< var(0)<< std::endl; return(0); } --------------------------- If I compile with "-O2", it prints 0, which is wrong. If I compile with "-O2 -fno-strict-aliasing", it prints the correct answer 1.6666..In every case I've looked at, when code gives the expected answer only when using -fno-strict-aliasing, it is because the code is using a type cast in an invalid way. In this case I would assume that the invalid type cast occurs in the blitz library code. Look for invalid type casts there.
Hi, thanks for the response! I've just posted my problem over at the blitz++ mailing list to see what they think about the matter.
It seems a bit strange to me that it would be a Blitz++ problem, since everything has worked fine using the same version of blitz++ (0.9) for a long time, with compiler versions all the way from after 4.1.3 up to and including 4.5.3. But not 4.6.1... Right now I don't remember if the strict-alising issue I had with 4.1.3 broke compilation or generated incorrect numerical results, though.
I'm no expert on GCC or Blitz++, so I'm not discounting anything. I'll await their opinion.
Torquil
