Comment by aleph_minus_one

> And on x86, saturating addition can't be done in a tick

Perhaps I misunderstand your point, but I am rather sure that in SSE.../AVX... there do exist instructions for saturating addition:

* (V)PADDSB, (V)PADDSW, (V)PADDUSB, (V)PADDUSW

* (V)PHADDSW, (V)PHSUBSW