Multiply and Divide functions ported from Crystal

3 files changed, 226 insertions, 2 deletions

diff --git a/engine/math/math.asm b/engine/math/math.asm
new file mode 100644
index 0000000..4395009
--- /dev/null
+++ b/engine/math/math.asm
@@ -0,0 +1,200 @@
+include "constants.asm"
+
+SECTION "Multiply and Divide Engine", ROMX [$6810], BANK [$1]
+
+_Multiply:: ; 6810
+
+; hMultiplier is one byte.
+	ld a, 8
+	ld b, a
+
+	xor a
+	ldh [hProduct], a
+	ldh [hMathBuffer + 1], a
+	ldh [hMathBuffer + 2], a
+	ldh [hMathBuffer + 3], a
+	ldh [hMathBuffer + 4], a
+
+
+.loop
+	ldh a, [hMultiplier]
+	srl a
+	ldh [hMultiplier], a
+	jr nc, .next
+
+	ldh a, [hMathBuffer + 4]
+	ld c, a
+	ldh a, [hMultiplicand + 2]
+	add c
+	ldh [hMathBuffer + 4], a
+
+	ldh a, [hMathBuffer + 3]
+	ld c, a
+	ldh a, [hMultiplicand + 1]
+	adc c
+	ldh [hMathBuffer + 3], a
+
+	ldh a, [hMathBuffer + 2]
+	ld c, a
+	ldh a, [hMultiplicand + 0]
+	adc c
+	ldh [hMathBuffer + 2], a
+
+	ldh a, [hMathBuffer + 1]
+	ld c, a
+	ldh a, [hProduct]
+	adc c
+	ldh [hMathBuffer + 1], a
+
+.next
+	dec b
+	jr z, .done
+
+
+; hMultiplicand <<= 1
+
+	ldh a, [hMultiplicand + 2]
+	add a
+	ldh [hMultiplicand + 2], a
+
+	ldh a, [hMultiplicand + 1]
+	rla
+	ldh [hMultiplicand + 1], a
+
+	ldh a, [hMultiplicand + 0]
+	rla
+	ldh [hMultiplicand + 0], a
+
+	ldh a, [hProduct]
+	rla
+	ldh [hProduct], a
+
+	jr .loop
+
+
+.done
+	ldh a, [hMathBuffer + 4]
+	ldh [hProduct + 3], a
+
+	ldh a, [hMathBuffer + 3]
+	ldh [hProduct + 2], a
+
+	ldh a, [hMathBuffer + 2]
+	ldh [hProduct + 1], a
+
+	ldh a, [hMathBuffer + 1]
+	ldh [hProduct + 0], a
+
+	ret
+; 6870
+
+
+_Divide:: ; 6870
+	xor a
+	ldh [hMathBuffer + 0], a
+	ldh [hMathBuffer + 1], a
+	ldh [hMathBuffer + 2], a
+	ldh [hMathBuffer + 3], a
+	ldh [hMathBuffer + 4], a
+
+	ld a, 9
+	ld e, a
+
+.loop
+	ldh a, [hMathBuffer + 0]
+	ld c, a
+	ldh a, [hDividend + 1]
+	sub c
+	ld d, a
+
+	ldh a, [hDivisor]
+	ld c, a
+	ldh a, [hDividend + 0]
+	sbc c
+	jr c, .next
+
+	ldh [hDividend + 0], a
+
+	ld a, d
+	ldh [hDividend + 1], a
+
+	ldh a, [hMathBuffer + 4]
+	inc a
+	ldh [hMathBuffer + 4], a
+
+	jr .loop
+
+.next
+	ld a, b
+	cp 1
+	jr z, .done
+
+	ldh a, [hMathBuffer + 4]
+	add a
+	ldh [hMathBuffer + 4], a
+
+	ldh a, [hMathBuffer + 3]
+	rla
+	ldh [hMathBuffer + 3], a
+
+	ldh a, [hMathBuffer + 2]
+	rla
+	ldh [hMathBuffer + 2], a
+
+	ldh a, [hMathBuffer + 1]
+	rla
+	ldh [hMathBuffer + 1], a
+
+	dec e
+	jr nz, .next2
+
+	ld e, 8
+	ldh a, [hMathBuffer + 0]
+	ldh [hDivisor], a
+	xor a
+	ldh [hMathBuffer + 0], a
+
+	ldh a, [hDividend + 1]
+	ldh [hDividend + 0], a
+
+	ldh a, [hDividend + 2]
+	ldh [hDividend + 1], a
+
+	ldh a, [hDividend + 3]
+	ldh [hDividend + 2], a
+
+.next2
+	ld a, e
+	cp 1
+	jr nz, .okay
+	dec b
+
+.okay
+	ldh a, [hDivisor]
+	srl a
+	ldh [hDivisor], a
+
+	ldh a, [hMathBuffer + 0]
+	rr a
+	ldh [hMathBuffer + 0], a
+
+	jr .loop
+
+.done
+	ldh a, [hDividend + 1]
+	ldh [hDivisor], a
+
+	ldh a, [hMathBuffer + 4]
+	ldh [hDividend + 3], a
+
+	ldh a, [hMathBuffer + 3]
+	ldh [hDividend + 2], a
+
+	ldh a, [hMathBuffer + 2]
+	ldh [hDividend + 1], a
+
+	ldh a, [hMathBuffer + 1]
+	ldh [hDividend + 0], a
+
+	ret
+; 68f3
diff --git a/hram.asm b/hram.asm
index c49ace3..0e26198 100644
--- a/hram.asm
+++ b/hram.asm
@@ -98,11 +98,37 @@ hSpriteOffset:: ; ffb1
 
     db ; TODO
 
+UNION
+
+; ffb3
+hProduct::
+hDividend::
+	; ds 4
+	db
+
+; ffb4
+hMultiplicand::
+hQuotient::
+	ds 3
+
+; ffb7
+hMultiplier::
+hDivisor::
+hRemainder::
+	db
+
+; ffb8
+hMathBuffer::
+	ds 5
+
+NEXTU
+
 hPrintNumLeadingDigit:: db ; ffb3 digit one place-value up
 hPrintNumDividend:: ds 3 ; ffb4 big-endian
 hPrintNumDivisor:: ds 3 ; ffb7 big-endian
 hPrintNumTemp:: ds 3 ; ffba big-endian
 
+ENDU
     ds 19 ; TODO
 
 
diff --git a/shim.sym b/shim.sym
index 540508d..8dd532b 100644
--- a/shim.sym
+++ b/shim.sym
@@ -54,8 +54,6 @@
 01:6445 Function6445
 01:66B1 Function66b1
 01:6713 Function6713
-01:6810 _Multiply
-01:6870 _Divide
 01:68F3 ItemAttributes
 
 02:4000 Function8000