21 ;; HL, DE (left, right irrelevant)
25 ;; 16-bit multiplication
32 ;; DE = less significant word of product
34 ;; Register used: AF,BC,DE,HL
40 ;; Optimise for the case when this side has 8 bits of data or
41 ;; less. This is often the case with support address calls.
48 ;; Taken from z88dk, which originally borrowed from the