Raymond Lu <songyulu@xxxxxxxxxxxx> writes: > Our HDF5 software has been having some data conversion problem with > GCC's optimization for a few years. One example is to convert data >>From short to int. You can find the program at > > ftp://ftp.hdfgroup.uiuc.edu/pub/outgoing/slu/tmp/ctest.c > > When I use "gcc -O2" or "gcc -O3" to compile it, I get wrong values > after the conversion. When I use "gcc -O0" or "gcc -O1", the values > are correct. /* This line causes the trouble. */ *((int*)d) = (int)(*((short*)s)); This is an aliasing violation. Read the documentation for the -fstrict-aliasing option. Ian
