1 files changed, 212 insertions, 0 deletions
diff --git a/engine/bcd.asm b/engine/bcd.asm
new file mode 100644
index 00000000..3e693e1f
--- /dev/null
+++ b/engine/bcd.asm
@@ -0,0 +1,212 @@
+DivideBCDPredef::
+DivideBCDPredef2::
+DivideBCDPredef3::
+DivideBCDPredef4::
+	call GetPredefRegisters
+
+DivideBCD::
+	xor a
+	ld [$ffa5], a
+	ld [$ffa6], a
+	ld [$ffa7], a
+	ld d, $1
+.asm_f72a
+	ld a, [$ffa2]
+	and $f0
+	jr nz, .asm_f75b
+	inc d
+	ld a, [$ffa2]
+	swap a
+	and $f0
+	ld b, a
+	ld a, [$ffa3]
+	swap a
+	ld [$ffa3], a
+	and $f
+	or b
+	ld [$ffa2], a
+	ld a, [$ffa3]
+	and $f0
+	ld b, a
+	ld a, [$ffa4]
+	swap a
+	ld [$ffa4], a
+	and $f
+	or b
+	ld [$ffa3], a
+	ld a, [$ffa4]
+	and $f0
+	ld [$ffa4], a
+	jr .asm_f72a
+.asm_f75b
+	push de
+	push de
+	call DivideBCD_f800
+	pop de
+	ld a, b
+	swap a
+	and $f0
+	ld [$ffa5], a
+	dec d
+	jr z, .asm_f7bc
+	push de
+	call DivideBCD_f7d7
+	call DivideBCD_f800
+	pop de
+	ld a, [$ffa5]
+	or b
+	ld [$ffa5], a
+	dec d
+	jr z, .asm_f7bc
+	push de
+	call DivideBCD_f7d7
+	call DivideBCD_f800
+	pop de
+	ld a, b
+	swap a
+	and $f0
+	ld [$ffa6], a
+	dec d
+	jr z, .asm_f7bc
+	push de
+	call DivideBCD_f7d7
+	call DivideBCD_f800
+	pop de
+	ld a, [$ffa6]
+	or b
+	ld [$ffa6], a
+	dec d
+	jr z, .asm_f7bc
+	push de
+	call DivideBCD_f7d7
+	call DivideBCD_f800
+	pop de
+	ld a, b
+	swap a
+	and $f0
+	ld [$ffa7], a
+	dec d
+	jr z, .asm_f7bc
+	push de
+	call DivideBCD_f7d7
+	call DivideBCD_f800
+	pop de
+	ld a, [$ffa7]
+	or b
+	ld [$ffa7], a
+.asm_f7bc
+	ld a, [$ffa5]
+	ld [$ffa2], a
+	ld a, [$ffa6]
+	ld [$ffa3], a
+	ld a, [$ffa7]
+	ld [$ffa4], a
+	pop de
+	ld a, $6
+	sub d
+	and a
+	ret z
+.asm_f7ce
+	push af
+	call DivideBCD_f7d7
+	pop af
+	dec a
+	jr nz, .asm_f7ce
+	ret
+
+DivideBCD_f7d7:
+	ld a, [$ffa4]
+	swap a
+	and $f
+	ld b, a
+	ld a, [$ffa3]
+	swap a
+	ld [$ffa3], a
+	and $f0
+	or b
+	ld [$ffa4], a
+	ld a, [$ffa3]
+	and $f
+	ld b, a
+	ld a, [$ffa2]
+	swap a
+	ld [$ffa2], a
+	and $f0
+	or b
+	ld [$ffa3], a
+	ld a, [$ffa2]
+	and $f
+	ld [$ffa2], a
+	ret
+
+DivideBCD_f800:
+	ld bc, $3
+.asm_f803
+	ld de, $ff9f
+	ld hl, $ffa2
+	push bc
+	call StringCmp
+	pop bc
+	ret c
+	inc b
+	ld de, $ffa1
+	ld hl, $ffa4
+	push bc
+	call SubBCD
+	pop bc
+	jr .asm_f803
+
+
+AddBCDPredef::
+	call GetPredefRegisters
+
+AddBCD::
+	and a
+	ld b, c
+.add
+	ld a, [de]
+	adc [hl]
+	daa
+	ld [de], a
+	dec de
+	dec hl
+	dec c
+	jr nz, .add
+	jr nc, .done
+	ld a, $99
+	inc de
+.fill
+	ld [de], a
+	inc de
+	dec b
+	jr nz, .fill
+.done
+	ret
+
+
+SubBCDPredef::
+	call GetPredefRegisters
+
+SubBCD::
+	and a
+	ld b, c
+.sub
+	ld a, [de]
+	sbc [hl]
+	daa
+	ld [de], a
+	dec de
+	dec hl
+	dec c
+	jr nz, .sub
+	jr nc, .done
+	ld a, $00
+	inc de
+.fill
+	ld [de], a
+	inc de
+	dec b
+	jr nz, .fill
+	scf
+.done
+	ret