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|
_Multiply: ; f660e (3d:660e)
ld a, $8
ld b, a
xor a
ld [H_PRODUCT], a ; $ff95
ld [H_MULTIPLYBUFFER], a ; $ff9b
ld [H_MULTIPLYBUFFER+1], a ; $ff9c
ld [H_MULTIPLYBUFFER+2], a ; $ff9d
ld [H_MULTIPLYBUFFER+3], a ; $ff9e
.multiplyLoop
ld a, [H_MULTIPLIER] ; $ff99
srl a
ld [H_MULTIPLIER], a ; $ff99
jr nc, .smallMultiplier ; less than $80
; code to possibly multiply the multiplicand by 2 and divide the multiplier by 2?
ld a, [H_MULTIPLYBUFFER+3]
ld c, a
ld a, [H_MULTIPLICAND+2]
add c
ld [H_MULTIPLYBUFFER+3], a
ld a, [H_MULTIPLYBUFFER+2]
ld c, a
ld a, [H_MULTIPLICAND+1]
adc c
ld [H_MULTIPLYBUFFER+2], a
ld a, [H_MULTIPLYBUFFER+1] ; $ff9c
ld c, a
ld a, [H_MULTIPLICAND] ; $ff96
adc c
ld [H_MULTIPLYBUFFER+1], a ; $ff9c
ld a, [H_MULTIPLYBUFFER]
ld c, a
ld a, [H_PRODUCT] ; $ff95
adc c
ld [H_MULTIPLYBUFFER], a
.smallMultiplier
dec b
jr z, .done
ld a, [H_MULTIPLICAND+2]
sla a
ld [H_MULTIPLICAND+2], a
ld a, [H_MULTIPLICAND+1]
rl a
ld [H_MULTIPLICAND+1], a
ld a, [H_MULTIPLICAND] ; $ff96
rl a
ld [H_MULTIPLICAND], a ; $ff96
ld a, [H_PRODUCT] ; $ff95
rl a
ld [H_PRODUCT], a ; $ff95
jr .multiplyLoop
.done
ld a, [H_MULTIPLYBUFFER+3]
ld [H_PRODUCT+3], a
ld a, [H_MULTIPLYBUFFER+2]
ld [H_PRODUCT+2], a
ld a, [H_MULTIPLYBUFFER+1] ; $ff9c
ld [H_PRODUCT+1], a ; $ff96
ld a, [H_MULTIPLYBUFFER]
ld [H_PRODUCT], a ; $ff95
ret
_Divide: ; f6672 (3d:6672)
xor a
ld [H_DIVIDEBUFFER], a ; ff9a
ld [H_DIVIDEBUFFER+1], a ; ff9b
ld [H_DIVIDEBUFFER+2], a ; ff9c
ld [H_DIVIDEBUFFER+3], a ; ff9d
ld [H_DIVIDEBUFFER+4], a ; ff9e
ld a, $9
ld e, a
.asm_f6680
ld a, [H_DIVIDEBUFFER]
ld c, a
ld a, [H_DIVIDEND+1] ; $ff96
sub c
ld d, a
ld a, [H_DIVISOR] ; $ff99
ld c, a
ld a, [H_DIVIDEND] ; $ff95
sbc c
jr c, .asm_f669b
ld [H_DIVIDEND], a ; $ff95
ld a, d
ld [H_DIVIDEND+1], a ; $ff96
ld a, [H_DIVIDEBUFFER+4]
inc a
ld [H_DIVIDEBUFFER+4], a
jr .asm_f6680
.asm_f669b
ld a, b
cp $1
jr z, .done
ld a, [H_DIVIDEBUFFER+4]
sla a
ld [H_DIVIDEBUFFER+4], a
ld a, [H_DIVIDEBUFFER+3]
rl a
ld [H_DIVIDEBUFFER+3], a
ld a, [H_DIVIDEBUFFER+2] ; $ff9c
rl a
ld [H_DIVIDEBUFFER+2], a ; $ff9c
ld a, [H_DIVIDEBUFFER+1]
rl a
ld [H_DIVIDEBUFFER+1], a
dec e
jr nz, .asm_f66d1
ld a, $8
ld e, a
ld a, [H_DIVIDEBUFFER]
ld [H_DIVISOR], a ; $ff99
xor a
ld [H_DIVIDEBUFFER], a
ld a, [H_DIVIDEND+1] ; $ff96
ld [H_DIVIDEND], a ; $ff95
ld a, [H_DIVIDEND+2]
ld [H_DIVIDEND+1], a ; $ff96
ld a, [H_DIVIDEND+3]
ld [H_DIVIDEND+2], a
.asm_f66d1
ld a, e
cp $1
jr nz, .asm_f66d7
dec b
.asm_f66d7
ld a, [H_DIVISOR] ; $ff99
srl a
ld [H_DIVISOR], a ; $ff99
ld a, [H_DIVIDEBUFFER]
rr a
ld [H_DIVIDEBUFFER], a
jr .asm_f6680
.done
ld a, [H_DIVIDEND+1] ; $ff96
ld [H_REMAINDER], a ; $ff99
ld a, [H_DIVIDEBUFFER+4]
ld [H_QUOTIENT+3], a
ld a, [H_DIVIDEBUFFER+3]
ld [H_QUOTIENT+2], a
ld a, [H_DIVIDEBUFFER+2] ; $ff9c
ld [H_QUOTIENT+1], a ; $ff96
ld a, [H_DIVIDEBUFFER+1]
ld [H_QUOTIENT], a ; $ff95
ret
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