1 files changed, 170 insertions, 0 deletions
diff --git a/home/save.asm b/home/save.asm
new file mode 100755
index 0000000..63cfaa8
--- /dev/null
+++ b/home/save.asm
@@ -0,0 +1,170 @@
+LoadSavedData: ; 0xf0c
+	call ValidateSaveData
+	ret nc
+.loop
+	ld a, [hli]
+	ld [de], a
+	inc de
+	dec bc
+	ld a, b
+	or c
+	jr nz, .loop
+	scf
+	ret
+
+SaveData: ; 0xf1a
+; Input: hl = data to save
+;        bc = number of bytes to save
+;        de = destination for saved data
+	push bc
+	push de
+	push hl
+.save
+	ld a, [hli]
+	ld [de], a
+	inc de
+	dec bc
+	ld a, b
+	or c
+	jr nz, .save
+	pop hl
+	pop de
+	pop bc
+	ld h, d
+	ld l, e
+	call SignData
+	call ComputeChecksum
+	call CreateBackupCopy
+	ret
+
+ValidateSaveData: ; 0xf34
+	call ValidateSignature
+	jr nc, .backup
+	call ValidateChecksum
+	jr nc, .backup
+	ret
+
+.backup
+	add hl, bc
+	inc hl
+	inc hl
+	inc hl
+	inc hl
+	call ValidateSignature
+	ret nc
+	call ValidateChecksum
+	ret
+
+CreateBackupCopy: ; 0xf4c
+	push bc
+	push hl
+	push de
+	inc bc
+	inc bc
+	inc bc
+	inc bc
+	ld d, h
+	ld e, l
+	add hl, bc
+.loop
+	ld a, [de]
+	ld [hli], a
+	inc de
+	dec bc
+	ld a, b
+	or c
+	jr nz, .loop
+	pop de
+	pop hl
+	pop bc
+	ret
+
+ValidateSignature: ; 0xf62
+	push hl
+	add hl, bc
+	ld a, [hli]
+	cp $4e
+	jr nz, .asm_f71
+	ld a, [hl]
+	cp $54
+	jr nz, .asm_f71
+	scf
+	jr .asm_f72
+
+.asm_f71
+	and a
+.asm_f72
+	pop hl
+	ret
+
+SignData: ; 0xf74
+	push hl
+	add hl, bc
+	ld a, $4e
+	ld [hli], a
+	ld a, $54
+	ld [hl], a
+	pop hl
+	ret
+
+ValidateChecksum: ; 0xf7e
+	push bc
+	push de
+	push hl
+	inc bc
+	inc bc
+	ld de, $0000
+.loop
+	ld a, [hli]
+	add e
+	ld e, a
+	jr nc, .asm_f8c
+	inc d
+.asm_f8c
+	dec bc
+	ld a, b
+	or c
+	jr nz, .loop
+	ld a, [hli]
+	cp e
+	jr nz, .fail
+	ld a, [hl]
+	cp d
+	jr nz, .fail
+	scf
+	jr .pass
+
+.fail
+	and a
+.pass
+	pop hl
+	pop de
+	pop bc
+	ret
+
+ComputeChecksum: ; 0xfa1
+	push bc
+	push de
+	push hl
+	inc bc
+	inc bc
+	ld de, $0000
+.loop
+	ld a, [hli]
+	add e
+	ld e, a
+	jr nc, .nocarry
+	inc d
+.nocarry
+	dec bc
+	ld a, b
+	or c
+	jr nz, .loop
+	ld a, e
+	ld [hli], a
+	ld a, d
+	ld [hl], a
+	pop hl
+	pop de
+	pop bc
+	ret