1 ;; Originally from GBDK by Pascal Felber.
15 ;; Need to sign extend before going in.
60 ;; HL, DE (left, right irrelivent)
64 ;; 16-bit multiplication
71 ;; DE = less significant word of product
73 ;; Register used: AF,BC,DE,HL
76 LD HL,#0x00 ; Product = 0
77 LD A,#15 ; Count = bit length - 1
78 ;; Shift-and-add algorithm
79 ;; If MSB of multiplier is 1, add multiplicand to partial product
80 ;; Shift partial product, multiplier left 1 bit
82 SLA E ; Shift multiplier left 1 bit
84 jp NC,.mlp1 ; Jump if MSB of multiplier = 0
85 ADD HL,BC ; Add multiplicand to partial product
87 ADD HL,HL ; Shift partial product left
89 jp NZ,.mlp ; Continue until count = 0
90 ;; Add multiplicand one last time if MSB of multiplier is 1
91 BIT 7,D ; Get MSB of multiplier
92 JR Z,.mend ; Exit if MSB of multiplier is 0
93 ADD HL,BC ; Add multiplicand to product