&gt; As I see it that&#x27;s a variant of PADDW, so whatever PADDW does is what matters, and PADDW does twos complement.<p>Nope, PADDW is a variant of PADDSW, so whatever PADDSW does is what matters, and PADDSW does saturating addition.<p>Or in other words: You are defining &quot;normal&quot; to mean &quot;twos-complement with wrap-around&quot; after all, which makes it rather unsurprising that every &quot;normal&quot; instruction according to your definition turns out to be doing twos-complement addition with wrap-around.<p>&gt; I thought about calling those out, I think it&#x27;s stretching too much to refer to an archaic instruction that works on &#x27;ascii&#x27; or such when we&#x27;re figuring the behavior of &#x27;integers&#x27;. Even if it is one byte.<p>Well, packed BCD definitely is not ASCII. Nor twos-complement, nor ones-complement, nor IEEE754. And BCD quite definitely represents a range of the integers.