CoCalc -- multiply

GitHub Repository: pret/pokered
Path: blob/master/engine/math/multiply_divide.asm
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_Multiply::
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	ld a, $8
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	ld b, a
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	xor a
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	ldh [hProduct], a
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	ldh [hMultiplyBuffer], a
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	ldh [hMultiplyBuffer+1], a
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	ldh [hMultiplyBuffer+2], a
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	ldh [hMultiplyBuffer+3], a
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.loop
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	ldh a, [hMultiplier]
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	srl a
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	ldh [hMultiplier], a ; (aliases: hDivisor, hMultiplier, hPowerOf10)
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	jr nc, .smallMultiplier
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	ldh a, [hMultiplyBuffer+3]
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	ld c, a
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	ldh a, [hMultiplicand+2]
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	add c
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	ldh [hMultiplyBuffer+3], a
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	ldh a, [hMultiplyBuffer+2]
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	ld c, a
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	ldh a, [hMultiplicand+1]
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	adc c
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	ldh [hMultiplyBuffer+2], a
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	ldh a, [hMultiplyBuffer+1]
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	ld c, a
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	ldh a, [hMultiplicand] ; (aliases: hMultiplicand)
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	adc c
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	ldh [hMultiplyBuffer+1], a
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	ldh a, [hMultiplyBuffer]
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	ld c, a
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	ldh a, [hProduct] ; (aliases: hProduct, hPastLeadingZeros, hQuotient)
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	adc c
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	ldh [hMultiplyBuffer], a
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.smallMultiplier
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	dec b
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	jr z, .done
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	ldh a, [hMultiplicand+2]
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	sla a
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	ldh [hMultiplicand+2], a
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	ldh a, [hMultiplicand+1]
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	rl a
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	ldh [hMultiplicand+1], a
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	ldh a, [hMultiplicand]
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	rl a
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	ldh [hMultiplicand], a
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	ldh a, [hProduct]
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	rl a
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	ldh [hProduct], a
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	jr .loop
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.done
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	ldh a, [hMultiplyBuffer+3]
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	ldh [hProduct+3], a
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	ldh a, [hMultiplyBuffer+2]
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	ldh [hProduct+2], a
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	ldh a, [hMultiplyBuffer+1]
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	ldh [hProduct+1], a
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	ldh a, [hMultiplyBuffer]
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	ldh [hProduct], a
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	ret
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_Divide::
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	xor a
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	ldh [hDivideBuffer], a
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	ldh [hDivideBuffer+1], a
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	ldh [hDivideBuffer+2], a
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	ldh [hDivideBuffer+3], a
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	ldh [hDivideBuffer+4], a
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	ld a, $9
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	ld e, a
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.loop
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	ldh a, [hDivideBuffer]
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	ld c, a
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	ldh a, [hDividend+1] ; (aliases: hMultiplicand)
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	sub c
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	ld d, a
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	ldh a, [hDivisor] ; (aliases: hDivisor, hMultiplier, hPowerOf10)
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	ld c, a
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	ldh a, [hDividend] ; (aliases: hProduct, hPastLeadingZeros, hQuotient)
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	sbc c
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	jr c, .next
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	ldh [hDividend], a ; (aliases: hProduct, hPastLeadingZeros, hQuotient)
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	ld a, d
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	ldh [hDividend+1], a ; (aliases: hMultiplicand)
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	ldh a, [hDivideBuffer+4]
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	inc a
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	ldh [hDivideBuffer+4], a
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	jr .loop
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.next
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	ld a, b
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	cp $1
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	jr z, .done
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	ldh a, [hDivideBuffer+4]
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	sla a
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	ldh [hDivideBuffer+4], a
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	ldh a, [hDivideBuffer+3]
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	rl a
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	ldh [hDivideBuffer+3], a
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	ldh a, [hDivideBuffer+2]
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	rl a
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	ldh [hDivideBuffer+2], a
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	ldh a, [hDivideBuffer+1]
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	rl a
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	ldh [hDivideBuffer+1], a
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	dec e
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	jr nz, .next2
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	ld a, $8
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	ld e, a
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	ldh a, [hDivideBuffer]
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	ldh [hDivisor], a ; (aliases: hDivisor, hMultiplier, hPowerOf10)
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	xor a
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	ldh [hDivideBuffer], a
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	ldh a, [hDividend+1] ; (aliases: hMultiplicand)
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	ldh [hDividend], a ; (aliases: hProduct, hPastLeadingZeros, hQuotient)
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	ldh a, [hDividend+2]
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	ldh [hDividend+1], a ; (aliases: hMultiplicand)
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	ldh a, [hDividend+3]
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	ldh [hDividend+2], a
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.next2
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	ld a, e
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	cp $1
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	jr nz, .okay
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	dec b
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.okay
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	ldh a, [hDivisor] ; (aliases: hDivisor, hMultiplier, hPowerOf10)
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	srl a
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	ldh [hDivisor], a ; (aliases: hDivisor, hMultiplier, hPowerOf10)
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	ldh a, [hDivideBuffer]
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	rr a
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	ldh [hDivideBuffer], a
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	jr .loop
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.done
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	ldh a, [hDividend+1] ; (aliases: hMultiplicand)
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	ldh [hRemainder], a ; (aliases: hDivisor, hMultiplier, hPowerOf10)
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	ldh a, [hDivideBuffer+4]
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	ldh [hQuotient+3], a
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	ldh a, [hDivideBuffer+3]
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	ldh [hQuotient+2], a
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	ldh a, [hDivideBuffer+2]
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	ldh [hQuotient+1], a ; (aliases: hMultiplicand)
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	ldh a, [hDivideBuffer+1]
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	ldh [hDividend], a ; (aliases: hProduct, hPastLeadingZeros, hQuotient)
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	ret
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