shithub: pokecrystal

ref: 33ff8f2aed95ec9d1d45d91c36a6d44a6edfce74
dir: /engine/math/math.asm/

_Multiply::
; hMultiplier is one byte.
	ld a, 8
	ld b, a

	xor a
	ld [hProduct], a
	ld [hMathBuffer + 1], a
	ld [hMathBuffer + 2], a
	ld [hMathBuffer + 3], a
	ld [hMathBuffer + 4], a

.loop
	ld a, [hMultiplier]
	srl a
	ld [hMultiplier], a
	jr nc, .next

	ld a, [hMathBuffer + 4]
	ld c, a
	ld a, [hMultiplicand + 2]
	add c
	ld [hMathBuffer + 4], a

	ld a, [hMathBuffer + 3]
	ld c, a
	ld a, [hMultiplicand + 1]
	adc c
	ld [hMathBuffer + 3], a

	ld a, [hMathBuffer + 2]
	ld c, a
	ld a, [hMultiplicand + 0]
	adc c
	ld [hMathBuffer + 2], a

	ld a, [hMathBuffer + 1]
	ld c, a
	ld a, [hProduct]
	adc c
	ld [hMathBuffer + 1], a

.next
	dec b
	jr z, .done

; hMultiplicand <<= 1

	ld a, [hMultiplicand + 2]
	add a
	ld [hMultiplicand + 2], a

	ld a, [hMultiplicand + 1]
	rla
	ld [hMultiplicand + 1], a

	ld a, [hMultiplicand + 0]
	rla
	ld [hMultiplicand + 0], a

	ld a, [hProduct]
	rla
	ld [hProduct], a

	jr .loop

.done
	ld a, [hMathBuffer + 4]
	ld [hProduct + 3], a

	ld a, [hMathBuffer + 3]
	ld [hProduct + 2], a

	ld a, [hMathBuffer + 2]
	ld [hProduct + 1], a

	ld a, [hMathBuffer + 1]
	ld [hProduct + 0], a

	ret

_Divide::
	xor a
	ld [hMathBuffer + 0], a
	ld [hMathBuffer + 1], a
	ld [hMathBuffer + 2], a
	ld [hMathBuffer + 3], a
	ld [hMathBuffer + 4], a

	ld a, 9
	ld e, a

.loop
	ld a, [hMathBuffer + 0]
	ld c, a
	ld a, [hDividend + 1]
	sub c
	ld d, a

	ld a, [hDivisor]
	ld c, a
	ld a, [hDividend + 0]
	sbc c
	jr c, .next

	ld [hDividend + 0], a

	ld a, d
	ld [hDividend + 1], a

	ld a, [hMathBuffer + 4]
	inc a
	ld [hMathBuffer + 4], a

	jr .loop

.next
	ld a, b
	cp 1
	jr z, .done

	ld a, [hMathBuffer + 4]
	add a
	ld [hMathBuffer + 4], a

	ld a, [hMathBuffer + 3]
	rla
	ld [hMathBuffer + 3], a

	ld a, [hMathBuffer + 2]
	rla
	ld [hMathBuffer + 2], a

	ld a, [hMathBuffer + 1]
	rla
	ld [hMathBuffer + 1], a

	dec e
	jr nz, .next2

	ld e, 8
	ld a, [hMathBuffer + 0]
	ld [hDivisor], a
	xor a
	ld [hMathBuffer + 0], a

	ld a, [hDividend + 1]
	ld [hDividend + 0], a

	ld a, [hDividend + 2]
	ld [hDividend + 1], a

	ld a, [hDividend + 3]
	ld [hDividend + 2], a

.next2
	ld a, e
	cp 1
	jr nz, .okay
	dec b

.okay
	ld a, [hDivisor]
	srl a
	ld [hDivisor], a

	ld a, [hMathBuffer + 0]
	rr a
	ld [hMathBuffer + 0], a

	jr .loop

.done
	ld a, [hDividend + 1]
	ld [hDivisor], a

	ld a, [hMathBuffer + 4]
	ld [hDividend + 3], a

	ld a, [hMathBuffer + 3]
	ld [hDividend + 2], a

	ld a, [hMathBuffer + 2]
	ld [hDividend + 1], a

	ld a, [hMathBuffer + 1]
	ld [hDividend + 0], a

	ret