;; cpHLDE [Maths]
;;  Compares HL to DE.
;; Output:
;;  Same as z80 CP instruction.
cpHLDE:
 or a
 sbc hl, de
 add hl,de
 ret
;; cpHLBC [Maths]
;;  Compares HL to BC.
;; Output:
;;  Same as z80 CP instruction.
cpHLBC:
 or a
 sbc hl, bc
 add hl,bc
 ret
;; cpBCDE [Maths]
;;  Compares DE to BC.
;; Output:
;;  Same as z80 CP instruction.
cpBCDE:
 push hl
  ld h, b
  ld l, c
  or a
  sbc hl, de
 pop hl
 ret

;; mulAbyB
;; Multiplys AxB
;; Inputs:
;;  A: Multiplier
;;  B: Multiplicand
;; Outputs:
;;  A: Product of A and B.
mulAbyB:
 push bc
  ld c, a
mulAbyBLoop:
  add a, c
  djnz mulAbyBLoop
  sub c
 pop bc
 ret

;; mulAbyHL
;; Multiplys AxHL
;; Inputs:
;;  A: Multiplier
;;  HL: Multiplicand
;; Outputs:
;;  HL: Product of A and HL.
mulAbyHL:
 push bc
 push de
  ld de, 0
  ex de, hl
  cp 0
  jr z, mulAbyHLEnd
  ld b, a
mulAbyHLLoop:
  add hl, de
  djnz mulAbyHLLoop
mulAbyHLEnd:
 pop de
 pop bc
 ret


;; mul32By8 [Maths]
;;  Performs an unsigned multiplication of DEHL and A.
;; Outputs:
;;  DEHL: product of DEHL and A
mul32By8:
    push bc \ push ix
        ld ixl, 8
        push de
            push hl
                ld hl, 0
                ld d, h
                ld e, l
mul32by8loop:
                add hl, hl
                rl e
                rl d
                rla
                jr nc, mul32by8noAdd
            pop bc
            add hl, bc
            ex (sp), hl
            push hl
                adc hl, de
            pop de
            ex de, hl
            ex (sp), hl
            push bc
mul32by8noAdd:
                dec ixl
                jr nz, mul32by8loop
            pop bc
        pop bc
    pop ix \ pop bc
    ret