If I have some aligned data (say from calling data() on a VectorXd), is it safe to create an aligned map starting anywhere in that data? For example:

Code: Select all

VectorXd awesome_vector = VectorXd::Random(10);
double* awesome_data = awesome_vector.data();
awesome_data += 3;
Map<Matrix2d,Aligned> awesome_map(awesome_data);


Thanks!

No, this is not safe. The pointer awesome_vector.data() is indeed aligned, but awesome_vector.data() + 3 may not be aligned.

In fact, if I compile and run your fragment on my computer (32-bits Linux) with SSE2 enabled (add the flag -msse2 when using GCC), then the program aborts with a message like

... Assertion ... "data is not aligned" failed