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..6cdc6c87
--- /dev/null
+++ b/engine/math/multiply_divide.asm
@@ -0,0 +1,143 @@
+_Multiply::
+	ld a, $8
+	ld b, a
+	xor a
+	ld [H_PRODUCT], a
+	ld [H_MULTIPLYBUFFER], a
+	ld [H_MULTIPLYBUFFER+1], a
+	ld [H_MULTIPLYBUFFER+2], a
+	ld [H_MULTIPLYBUFFER+3], a
+.loop
+	ld a, [H_MULTIPLIER]
+	srl a
+	ld [H_MULTIPLIER], a ; (aliases: H_DIVISOR, H_MULTIPLIER, H_POWEROFTEN)
+	jr nc, .smallMultiplier
+	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]
+	ld c, a
+	ld a, [H_MULTIPLICAND] ; (aliases: H_MULTIPLICAND)
+	adc c
+	ld [H_MULTIPLYBUFFER+1], a
+	ld a, [H_MULTIPLYBUFFER]
+	ld c, a
+	ld a, [H_PRODUCT] ; (aliases: H_PRODUCT, H_PASTLEADINGZEROES, H_QUOTIENT)
+	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]
+	rl a
+	ld [H_MULTIPLICAND], a
+	ld a, [H_PRODUCT]
+	rl a
+	ld [H_PRODUCT], a
+	jr .loop
+.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]
+	ld [H_PRODUCT+1], a
+	ld a, [H_MULTIPLYBUFFER]
+	ld [H_PRODUCT], a
+	ret
+
+_Divide::
+	xor a
+	ld [H_DIVIDEBUFFER], a
+	ld [H_DIVIDEBUFFER+1], a
+	ld [H_DIVIDEBUFFER+2], a
+	ld [H_DIVIDEBUFFER+3], a
+	ld [H_DIVIDEBUFFER+4], a
+	ld a, $9
+	ld e, a
+.asm_37db3
+	ld a, [H_DIVIDEBUFFER]
+	ld c, a
+	ld a, [H_DIVIDEND+1] ; (aliases: H_MULTIPLICAND)
+	sub c
+	ld d, a
+	ld a, [H_DIVISOR] ; (aliases: H_DIVISOR, H_MULTIPLIER, H_POWEROFTEN)
+	ld c, a
+	ld a, [H_DIVIDEND] ; (aliases: H_PRODUCT, H_PASTLEADINGZEROES, H_QUOTIENT)
+	sbc c
+	jr c, .asm_37dce
+	ld [H_DIVIDEND], a ; (aliases: H_PRODUCT, H_PASTLEADINGZEROES, H_QUOTIENT)
+	ld a, d
+	ld [H_DIVIDEND+1], a ; (aliases: H_MULTIPLICAND)
+	ld a, [H_DIVIDEBUFFER+4]
+	inc a
+	ld [H_DIVIDEBUFFER+4], a
+	jr .asm_37db3
+.asm_37dce
+	ld a, b
+	cp $1
+	jr z, .asm_37e18
+	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]
+	rl a
+	ld [H_DIVIDEBUFFER+2], a
+	ld a, [H_DIVIDEBUFFER+1]
+	rl a
+	ld [H_DIVIDEBUFFER+1], a
+	dec e
+	jr nz, .asm_37e04
+	ld a, $8
+	ld e, a
+	ld a, [H_DIVIDEBUFFER]
+	ld [H_DIVISOR], a ; (aliases: H_DIVISOR, H_MULTIPLIER, H_POWEROFTEN)
+	xor a
+	ld [H_DIVIDEBUFFER], a
+	ld a, [H_DIVIDEND+1] ; (aliases: H_MULTIPLICAND)
+	ld [H_DIVIDEND], a ; (aliases: H_PRODUCT, H_PASTLEADINGZEROES, H_QUOTIENT)
+	ld a, [H_DIVIDEND+2]
+	ld [H_DIVIDEND+1], a ; (aliases: H_MULTIPLICAND)
+	ld a, [H_DIVIDEND+3]
+	ld [H_DIVIDEND+2], a
+.asm_37e04
+	ld a, e
+	cp $1
+	jr nz, .asm_37e0a
+	dec b
+.asm_37e0a
+	ld a, [H_DIVISOR] ; (aliases: H_DIVISOR, H_MULTIPLIER, H_POWEROFTEN)
+	srl a
+	ld [H_DIVISOR], a ; (aliases: H_DIVISOR, H_MULTIPLIER, H_POWEROFTEN)
+	ld a, [H_DIVIDEBUFFER]
+	rr a
+	ld [H_DIVIDEBUFFER], a
+	jr .asm_37db3
+.asm_37e18
+	ld a, [H_DIVIDEND+1] ; (aliases: H_MULTIPLICAND)
+	ld [H_REMAINDER], a ; (aliases: H_DIVISOR, H_MULTIPLIER, H_POWEROFTEN)
+	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]
+	ld [H_QUOTIENT+1], a ; (aliases: H_MULTIPLICAND)
+	ld a, [H_DIVIDEBUFFER+1]
+	ld [H_DIVIDEND], a ; (aliases: H_PRODUCT, H_PASTLEADINGZEROES, H_QUOTIENT)
+	ret