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z80_unpacker: add backward variant of unpacker + example extended

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This commit is contained in:
Peter Helcmanovsky (Ped)
2022-09-18 00:23:14 +02:00
parent 3c773aca8d
commit b13fa05413
7 changed files with 80 additions and 21 deletions
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71
z80_unpacker/example/example.asm
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@@ -3,7 +3,8 @@
DEVICE ZXSPECTRUM48,$8FFF
ORG $9000
compressed_scr_files: ; border color byte + upkr-packed .scr file
;; forward example data
compressed_scr_files.fwd: ; border color byte + upkr-packed .scr file
DB 1
INCBIN "screens/Grongy - ZX Spectrum (2022).scr.upk"
DB 7
@@ -13,37 +14,87 @@ compressed_scr_files: ; border color byte + upkr-packed .scr file
DB 6
INCBIN "screens/diver - Back to Bjork (2015).scr.upk"
.e:
;; backward example data (unpacker goes from the end of the data!)
compressed_scr_files.rwd.e: EQU $-1 ; the final IX will point one byte ahead of "$" here
INCBIN "screens.reversed/diver - Back to Bjork (2015).scr.upk"
DB 6
INCBIN "screens.reversed/diver - Mercenary 4. The Heaven's Devil (2014) (Forever 2014 Olympic Edition, 1).scr.upk"
DB 0
INCBIN "screens.reversed/Schafft - Poison (2017).scr.upk"
DB 7
INCBIN "screens.reversed/Grongy - ZX Spectrum (2022).scr.upk"
compressed_scr_files.rwd: ; border color byte + upkr-packed .scr file (backward)
DB 1
start:
di
; OPT --zxnext
; nextreg 7,3 ; ZX Next: switch to 28Mhz
ld ix,compressed_scr_files
.slideshow_loop
;;; FORWARD packed/unpacked data demo
ld ix,compressed_scr_files.fwd
.slideshow_loop.fwd:
; set BORDER for next image
ldi a,(ix) ; fake: ld a,(ix) : inc ix
ld a,(ix)
inc ix
out (254),a
; call unpack of next image directly into VRAM
ld de,$4000 ; target VRAM
exx
; IX = packed data, DE' = destination ($4000)
; returned IX will point right after the packed data
call upkr.unpack
call fwd.upkr.unpack
; do some busy loop with CPU to delay between images
call delay
; check if all images were displayed, loop around from first one then
ld a,ixl
cp low compressed_scr_files.fwd.e
jr nz,.slideshow_loop.fwd
;;; BACKWARD packed/unpacked data demo
ld ix,compressed_scr_files.rwd
.slideshow_loop.rwd:
; set BORDER for next image
ld a,(ix)
dec ix
out (254),a
; call unpack of next image directly into VRAM
ld de,$5AFF ; target VRAM
exx
; IX = packed data, DE' = destination
; returned IX will point right ahead of the packed data
call rwd.upkr.unpack
; do some busy loop with CPU to delay between images
call delay
; check if all images were displayed, loop around from first one then
ld a,ixl
cp low compressed_scr_files.rwd.e
jr nz,.slideshow_loop.rwd
jr start
delay:
ld bc,$AA00
.delay:
.8 ex (sp),ix
dec c
jr nz,.delay
djnz .delay
; check if all images were displayed, loop around from first one then
ld a,ixl
cp low compressed_scr_files.e
jr z,start
jr .slideshow_loop
ret
; include the depacker library, optionally putting probs array buffer near end of RAM
DEFINE UPKR_PROBS_ORIGIN $FA00 ; if not defined, array will be put after unpack code
MODULE fwd
INCLUDE "../unpack.asm"
ENDMODULE
MODULE rwd
DEFINE BACKWARDS_UNPACK ; defined to build backwards unpack
; initial IX points at last byte of compressed data
; initial DE' points at last byte of unpacked data
INCLUDE "../unpack.asm"
ENDMODULE
SAVESNA "example.sna",start

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z80_unpacker/example/example.sna
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z80_unpacker/example/screens.reversed/Grongy - ZX Spectrum (2022).scr.upk Normal file
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z80_unpacker/example/screens.reversed/Schafft - Poison (2017).scr.upk Normal file
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z80_unpacker/example/screens.reversed/diver - Back to Bjork (2015).scr.upk Normal file
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z80_unpacker/example/screens.reversed/diver - Mercenary 4. The Heaven's Devil (2014) (Forever 2014 Olympic Edition, 1).scr.upk Normal file
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20
z80_unpacker/unpack.asm
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@@ -15,6 +15,10 @@
;; modifies: all registers except IY, requires 10 bytes of stack space
;;
; DEFINE BACKWARDS_UNPACK ; uncomment to build backwards depacker
; initial IX points at last byte of compressed data
; initial DE' points at last byte of unpacked data
; DEFINE UPKR_UNPACK_SPEED ; uncomment to get larger but faster unpack routine
OPT push reset --syntax=abf
@@ -102,7 +106,7 @@ unpack:
ld a,c
exx
ld (de),a ; *write_ptr++ = byte;
inc de
IFNDEF BACKWARDS_UNPACK : inc de : ELSE : dec de : ENDIF
exx
ld d,b ; prev_was_match = false
jr .decompress_data
@@ -139,9 +143,13 @@ unpack:
ld h,d ; DE = write_ptr
ld l,e
.offset+*: ld bc,0
IFNDEF BACKWARDS_UNPACK
sbc hl,bc ; CF=0 from decode_number ; HL = write_ptr - offset
ELSE
add hl,bc ; HL = write_ptr + offset
ENDIF
pop bc ; BC = length
ldir
IFNDEF BACKWARDS_UNPACK : ldir : ELSE : lddr : ENDIF
exx
ld d,b ; prev_was_match = true
djnz .decompress_data ; adjust context_index back to 0..255 range, go to main loop
@@ -195,7 +203,7 @@ decode_bit:
jr nz,.has_bit ; CF=data, ZF=0 -> some bits + stop bit still available
; CF=1 (by stop bit)
ld a,(ix)
inc ix ; upkr_current_byte = *upkr_data_ptr++;
IFNDEF BACKWARDS_UNPACK : inc ix : ELSE : dec ix : ENDIF ; upkr_current_byte = *upkr_data_ptr++;
adc a,a ; CF=data, b0=1 as new stop bit
.has_bit:
adc hl,hl ; upkr_state = (upkr_state << 1) + (upkr_current_byte >> 7);
@@ -306,10 +314,10 @@ decode_number:
; reserve space for probs array without emitting any machine code (using only EQU)
IFDEF UPKR_PROBS_ORIGIN ; if specific address is defined by user, move probs array there
ORG UPKR_PROBS_ORIGIN
probs: EQU ((UPKR_PROBS_ORIGIN) + 255) & -$100 ; probs array aligned to 256
ELSE
probs: EQU ($ + 255) & -$100 ; probs array aligned to 256
ENDIF
probs: EQU ($+255) & -$100 ; probs array aligned to 256
.real_c: EQU 1 + 255 + 1 + 2*NUMBER_BITS ; real size of probs array
.c: EQU (.real_c + 1) & -2 ; padding to even size (required by init code)
.e: EQU probs + .c