an sse vector can hold 4 floats and 2 doubles so one needs to test more cases with floats, e.g. 0 1, 2, 3 elements must be peeled vs 0, 1 elements.
Its a little paranoid as if 1 unaligned work the rest probably does too (especially as they all use the same loop primitives). Might be one of the improvements for _gen_alignment_data later.