First-up chord algorithm

first-up.c

Chord prev_keys = NONE, can_trigger = ALL;

void process_sample(Chord keys) {
	Chord released = prev_keys & ~keys;
	if(released & can_trigger) {
		send_chord(prev_keys);
		// These keys do not fire a chord the next time they are released.
		can_trigger = ~keys;
	}
	
	prev_keys = keys;
	// Keys which have been released can now fire a chord again.
	can_trigger |= ~keys;
}