1 files changed, 143 insertions, 0 deletions
diff --git a/engine/math/multiply_divide.asm b/engine/math/multiply_divide.asm
new file mode 100755
index 00000000..2fcda158
--- /dev/null
+++ b/engine/math/multiply_divide.asm
@@ -0,0 +1,143 @@
+_Multiply::
+	ld a, $8
+	ld b, a
+	xor a
+	ldh [hProduct], a
+	ldh [hMultiplyBuffer], a
+	ldh [hMultiplyBuffer+1], a
+	ldh [hMultiplyBuffer+2], a
+	ldh [hMultiplyBuffer+3], a
+.loop
+	ldh a, [hMultiplier]
+	srl a
+	ldh [hMultiplier], a ; (aliases: hDivisor, hMultiplier, hPowerOf10)
+	jr nc, .smallMultiplier
+	ldh a, [hMultiplyBuffer+3]
+	ld c, a
+	ldh a, [hMultiplicand+2]
+	add c
+	ldh [hMultiplyBuffer+3], a
+	ldh a, [hMultiplyBuffer+2]
+	ld c, a
+	ldh a, [hMultiplicand+1]
+	adc c
+	ldh [hMultiplyBuffer+2], a
+	ldh a, [hMultiplyBuffer+1]
+	ld c, a
+	ldh a, [hMultiplicand] ; (aliases: hMultiplicand)
+	adc c
+	ldh [hMultiplyBuffer+1], a
+	ldh a, [hMultiplyBuffer]
+	ld c, a
+	ldh a, [hProduct] ; (aliases: hProduct, hPastLeadingZeros, hQuotient)
+	adc c
+	ldh [hMultiplyBuffer], a
+.smallMultiplier
+	dec b
+	jr z, .done
+	ldh a, [hMultiplicand+2]
+	sla a
+	ldh [hMultiplicand+2], a
+	ldh a, [hMultiplicand+1]
+	rl a
+	ldh [hMultiplicand+1], a
+	ldh a, [hMultiplicand]
+	rl a
+	ldh [hMultiplicand], a
+	ldh a, [hProduct]
+	rl a
+	ldh [hProduct], a
+	jr .loop
+.done
+	ldh a, [hMultiplyBuffer+3]
+	ldh [hProduct+3], a
+	ldh a, [hMultiplyBuffer+2]
+	ldh [hProduct+2], a
+	ldh a, [hMultiplyBuffer+1]
+	ldh [hProduct+1], a
+	ldh a, [hMultiplyBuffer]
+	ldh [hProduct], a
+	ret
+
+_Divide::
+	xor a
+	ldh [hDivideBuffer], a
+	ldh [hDivideBuffer+1], a
+	ldh [hDivideBuffer+2], a
+	ldh [hDivideBuffer+3], a
+	ldh [hDivideBuffer+4], a
+	ld a, $9
+	ld e, a
+.asm_37db3
+	ldh a, [hDivideBuffer]
+	ld c, a
+	ldh a, [hDividend+1] ; (aliases: hMultiplicand)
+	sub c
+	ld d, a
+	ldh a, [hDivisor] ; (aliases: hDivisor, hMultiplier, hPowerOf10)
+	ld c, a
+	ldh a, [hDividend] ; (aliases: hProduct, hPastLeadingZeros, hQuotient)
+	sbc c
+	jr c, .asm_37dce
+	ldh [hDividend], a ; (aliases: hProduct, hPastLeadingZeros, hQuotient)
+	ld a, d
+	ldh [hDividend+1], a ; (aliases: hMultiplicand)
+	ldh a, [hDivideBuffer+4]
+	inc a
+	ldh [hDivideBuffer+4], a
+	jr .asm_37db3
+.asm_37dce
+	ld a, b
+	cp $1
+	jr z, .asm_37e18
+	ldh a, [hDivideBuffer+4]
+	sla a
+	ldh [hDivideBuffer+4], a
+	ldh a, [hDivideBuffer+3]
+	rl a
+	ldh [hDivideBuffer+3], a
+	ldh a, [hDivideBuffer+2]
+	rl a
+	ldh [hDivideBuffer+2], a
+	ldh a, [hDivideBuffer+1]
+	rl a
+	ldh [hDivideBuffer+1], a
+	dec e
+	jr nz, .asm_37e04
+	ld a, $8
+	ld e, a
+	ldh a, [hDivideBuffer]
+	ldh [hDivisor], a ; (aliases: hDivisor, hMultiplier, hPowerOf10)
+	xor a
+	ldh [hDivideBuffer], a
+	ldh a, [hDividend+1] ; (aliases: hMultiplicand)
+	ldh [hDividend], a ; (aliases: hProduct, hPastLeadingZeros, hQuotient)
+	ldh a, [hDividend+2]
+	ldh [hDividend+1], a ; (aliases: hMultiplicand)
+	ldh a, [hDividend+3]
+	ldh [hDividend+2], a
+.asm_37e04
+	ld a, e
+	cp $1
+	jr nz, .asm_37e0a
+	dec b
+.asm_37e0a
+	ldh a, [hDivisor] ; (aliases: hDivisor, hMultiplier, hPowerOf10)
+	srl a
+	ldh [hDivisor], a ; (aliases: hDivisor, hMultiplier, hPowerOf10)
+	ldh a, [hDivideBuffer]
+	rr a
+	ldh [hDivideBuffer], a
+	jr .asm_37db3
+.asm_37e18
+	ldh a, [hDividend+1] ; (aliases: hMultiplicand)
+	ldh [hRemainder], a ; (aliases: hDivisor, hMultiplier, hPowerOf10)
+	ldh a, [hDivideBuffer+4]
+	ldh [hQuotient+3], a
+	ldh a, [hDivideBuffer+3]
+	ldh [hQuotient+2], a
+	ldh a, [hDivideBuffer+2]
+	ldh [hQuotient+1], a ; (aliases: hMultiplicand)
+	ldh a, [hDivideBuffer+1]
+	ldh [hDividend], a ; (aliases: hProduct, hPastLeadingZeros, hQuotient)
+	ret