Re: [boost] interest in structure of arrays container?

On 10/26/2016 02:27 AM, Michael Marcin wrote: [snip]

Perhaps I'm misunderstanding. Using your struct above: std::array< soa_align, 4 > data; std::cout << "align array: " << alignof(decltype(data)) << '\n' << "size element: " << sizeof( data[0] ) << '\n' << "size array: " << sizeof( data ) << '\n' << "offset[1]: " << (char*)&(data[1]) - (char*)data.data() << '\n';

align array: 16 size element: 16 size array: 64 offset[1]: 16

For data to work with SSE instructions this needs to report:

align array: 16 size element: 4 size array: 16 offset[1]: 4

i.e. 4 floats have to be contiguous in memory, and the *first* float has to be aligned to 16 bytes.

So why not: alignas(16) std::array data; IOW, does the decltype(data) have to have the required alignment or does &data have to have that alignment?