16 ;; hl, de (left, right irrelevant)
20 ;; 16-bit multiplication
27 ;; hl = less significant word of product
29 ;; Register used: AF,BC,DE,HL
36 ;; Optimise for the case when this side has 8 bits of data or
37 ;; less. This is often the case with support address calls.
42 ;; Taken from z88dk, which originally borrowed from the