Thank you for a detailed reply, nice to read. A small hack could be using a very modern sophisticated clang compiler, to produce an optimized assembly for an i

Thank you for a detailed reply, nice to read. A small hack could be using a very modern sophisticated clang compiler, to produce an optimized assembly for an idiom you need, coded in C. Like clang -S a.c then you change and hard-code what you like. Yes, it is a non-trivial task, so, it might make you much better engineer, like a difficult journey into unknown improves you.