First Commit

Upload literally everything from the pokecrystal16 expand-move-ID branch

home/decompress.asm

@@ -0,0 +1,317 @@
+FarDecompress::
+; Decompress graphics data from a:hl to de.
+
+	ld [wLZBank], a
+	ldh a, [hROMBank]
+	push af
+	ld a, [wLZBank]
+	rst Bankswitch
+
+	call Decompress
+
+	pop af
+	rst Bankswitch
+	ret
+
+Decompress::
+; Pokemon GSC uses an lz variant (lz3) for compression.
+; This is mainly (but not necessarily) used for graphics.
+
+; This function decompresses lz-compressed data from hl to de.
+
+DEF LZ_END EQU $ff ; Compressed data is terminated with $ff.
+
+; A typical control command consists of:
+
+DEF LZ_CMD EQU %11100000 ; command id (bits 5-7)
+DEF LZ_LEN EQU %00011111 ; length n   (bits 0-4)
+
+; Additional parameters are read during command execution.
+
+; Commands:
+
+DEF LZ_LITERAL   EQU 0 << 5 ; Read literal data for n bytes.
+DEF LZ_ITERATE   EQU 1 << 5 ; Write the same byte for n bytes.
+DEF LZ_ALTERNATE EQU 2 << 5 ; Alternate two bytes for n bytes.
+DEF LZ_ZERO      EQU 3 << 5 ; Write 0 for n bytes.
+
+; Another class of commands reuses data from the decompressed output.
+DEF LZ_RW        EQU 2 + 5 ; bit
+
+; These commands take a signed offset to start copying from.
+; Wraparound is simulated.
+; Positive offsets (15-bit) are added to the start address.
+; Negative offsets (7-bit) are subtracted from the current position.
+
+DEF LZ_REPEAT    EQU 4 << 5 ; Repeat n bytes from the offset.
+DEF LZ_FLIP      EQU 5 << 5 ; Repeat n bitflipped bytes.
+DEF LZ_REVERSE   EQU 6 << 5 ; Repeat n bytes in reverse.
+
+; If the value in the count needs to be larger than 5 bits,
+; LZ_LONG can be used to expand the count to 10 bits.
+DEF LZ_LONG      EQU 7 << 5
+
+; A new control command is read in bits 2-4.
+; The top two bits of the length are bits 0-1.
+; Another byte is read containing the bottom 8 bits.
+DEF LZ_LONG_HI   EQU %00000011
+
+; In other words, the structure of the command becomes
+; 111xxxyy yyyyyyyy
+; x: the new control command
+; y: the length
+
+	; Save the output address
+	; for rewrite commands.
+	ld a, e
+	ld [wLZAddress], a
+	ld a, d
+	ld [wLZAddress + 1], a
+
+.Main:
+	ld a, [hl]
+	cp LZ_END
+	ret z
+
+	and LZ_CMD
+
+	cp LZ_LONG
+	jr nz, .short
+
+; The count is now 10 bits.
+
+	; Read the next 3 bits.
+	; %00011100 -> %11100000
+	ld a, [hl]
+	add a
+	add a ; << 3
+	add a
+
+	; This is our new control code.
+	and LZ_CMD
+	push af
+
+	ld a, [hli]
+	and LZ_LONG_HI
+	ld b, a
+	ld a, [hli]
+	ld c, a
+
+	; read at least 1 byte
+	inc bc
+	jr .command
+
+.short
+	push af
+
+	ld a, [hli]
+	and LZ_LEN
+	ld c, a
+	ld b, 0
+
+	; read at least 1 byte
+	inc c
+
+.command
+	; Increment loop counts.
+	; We bail the moment they hit 0.
+	inc b
+	inc c
+
+	pop af
+
+	bit LZ_RW, a
+	jr nz, .rewrite
+
+	cp LZ_ITERATE
+	jr z, .Iter
+	cp LZ_ALTERNATE
+	jr z, .Alt
+	cp LZ_ZERO
+	jr z, .Zero
+
+; Literal
+; Read literal data for bc bytes.
+.lloop
+	dec c
+	jr nz, .lnext
+	dec b
+	jp z, .Main
+
+.lnext
+	ld a, [hli]
+	ld [de], a
+	inc de
+	jr .lloop
+
+.Iter:
+; Write the same byte for bc bytes.
+	ld a, [hli]
+
+.iloop
+	dec c
+	jr nz, .inext
+	dec b
+	jp z, .Main
+
+.inext
+	ld [de], a
+	inc de
+	jr .iloop
+
+.Alt:
+; Alternate two bytes for bc bytes.
+	dec c
+	jr nz, .anext1
+	dec b
+	jp z, .adone1
+.anext1
+	ld a, [hli]
+	ld [de], a
+	inc de
+
+	dec c
+	jr nz, .anext2
+	dec b
+	jp z, .adone2
+.anext2
+	ld a, [hld]
+	ld [de], a
+	inc de
+
+	jr .Alt
+
+	; Skip past the bytes we were alternating.
+.adone1
+	inc hl
+.adone2
+	inc hl
+	jr .Main
+
+.Zero:
+; Write 0 for bc bytes.
+	xor a
+
+.zloop
+	dec c
+	jr nz, .znext
+	dec b
+	jp z, .Main
+
+.znext
+	ld [de], a
+	inc de
+	jr .zloop
+
+.rewrite
+; Repeat decompressed data from output.
+	push hl
+	push af
+
+	ld a, [hli]
+	bit 7, a ; sign
+	jr z, .positive
+
+; negative
+	; hl = de + -a
+	and %01111111
+	cpl
+	add e
+	ld l, a
+	ld a, -1
+	adc d
+	ld h, a
+	jr .ok
+
+.positive
+; Positive offsets are two bytes.
+	ld l, [hl]
+	ld h, a
+	; add to starting output address
+	ld a, [wLZAddress]
+	add l
+	ld l, a
+	ld a, [wLZAddress + 1]
+	adc h
+	ld h, a
+
+.ok
+	pop af
+
+	cp LZ_REPEAT
+	jr z, .Repeat
+	cp LZ_FLIP
+	jr z, .Flip
+	cp LZ_REVERSE
+	jr z, .Reverse
+
+; Since LZ_LONG is command 7,
+; only commands 0-6 are passed in.
+; This leaves room for an extra command 7.
+; However, lengths longer than 768
+; would be interpreted as LZ_END.
+
+; More practically, LZ_LONG is not recursive.
+; For now, it defaults to LZ_REPEAT.
+
+.Repeat:
+; Copy decompressed data for bc bytes.
+	dec c
+	jr nz, .rnext
+	dec b
+	jr z, .donerw
+
+.rnext
+	ld a, [hli]
+	ld [de], a
+	inc de
+	jr .Repeat
+
+.Flip:
+; Copy bitflipped decompressed data for bc bytes.
+	dec c
+	jr nz, .fnext
+	dec b
+	jp z, .donerw
+
+.fnext
+	ld a, [hli]
+	push bc
+	lb bc, 0, 8
+
+.floop
+	rra
+	rl b
+	dec c
+	jr nz, .floop
+
+	ld a, b
+	pop bc
+
+	ld [de], a
+	inc de
+	jr .Flip
+
+.Reverse:
+; Copy reversed decompressed data for bc bytes.
+	dec c
+	jr nz, .rvnext
+
+	dec b
+	jp z, .donerw
+
+.rvnext
+	ld a, [hld]
+	ld [de], a
+	inc de
+	jr .Reverse
+
+.donerw
+	pop hl
+
+	bit 7, [hl]
+	jr nz, .next
+	inc hl ; positive offset is two bytes
+.next
+	inc hl
+	jp .Main