IsInArray::
; Find value a for every de bytes in array hl.
; Return index in b and carry if found.

	ld b, 0
	ld c, a
.loop
	ld a, [hl]
	cp -1
	jr z, .NotInArray
	cp c
	jr z, .InArray
	inc b
	add hl, de
	jr .loop

.NotInArray:
	and a
	ret

.InArray:
	scf
	ret