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Merge pull request #3 from ped7g/z80_ped7g

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backward unpacker + example extended
This commit is contained in:
exoticorn
2022-09-18 23:24:28 +02:00
committed by GitHub
parent a5406deb30 165f593a11
commit 7b0e22f459
7 changed files with 115 additions and 37 deletions
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77
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
; nextreg 7,3 ; ZX Next: switch to 28Mhz
;;; 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
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
INCLUDE "../unpack.asm"
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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75
z80_unpacker/unpack.asm
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@@ -15,6 +15,12 @@
;; 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
MODULE upkr
@@ -100,7 +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
@@ -137,9 +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
@@ -193,7 +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);
@@ -215,6 +225,10 @@ decode_bit:
ld d,0
ld e,a ; DE = state_scale ; prob || (256-prob)
ld l,d ; H:L = (upkr_state>>8) : 0
IFNDEF UPKR_UNPACK_SPEED
;; looped MUL for minimum unpack size
ld b,8 ; counter
.mulLoop:
add hl,hl
@@ -222,28 +236,41 @@ decode_bit:
add hl,de
.mul0:
djnz .mulLoop ; until HL = state_scale * (upkr_state>>8), also BC becomes (upkr_state & 255)
ELSE
;;; unrolled MUL for better performance, +25 bytes unpack size
ld b,d
DUP 8
add hl,hl
jr nc,0_f
add hl,de
0:
EDUP
ENDIF
add hl,bc ; HL = state_scale * (upkr_state >> 8) + (upkr_state & 255)
pop af
ld d,-16 ; D = -prob_offset (-16 0xF0 when bit = 0)
pop af ; restore prob and CF=bit
jr nc,.bit_is_0_2
ld d,b ; D = -prob_offset (0 when bit = 1) (also does fix following ADD)
dec h
add hl,de ; HL += -prob (HL += (256 - prob) - 256)
.bit_is_0_2: ; HL = state_offset + state_scale * (upkr_state >> 8) + (upkr_state & 255) ; new upkr_state
dec d ; DE = -prob (also D = bit ? $FF : $00)
add hl,de ; HL += -prob
; ^ this always preserves CF=1, because (state>>8) >= 128, state_scale: 7..250, prob: 7..250,
; so 7*128 > 250 and thus edge case `ADD hl=(7*128+0),de=(-250)` => CF=1
.bit_is_0_2:
; *** adjust probs[context_index]
ld e,a ; D:E = -prob_offset:prob, A = prob
and $F8
ld e,a ; preserve prob
rra ; + (bit<<4) ; part of -prob_offset, needs another -16
and $FC ; clear/keep correct bits to get desired (prob>>4) + extras, CF=0
rra
rra
rra
rra
adc a,d ; A = -prob_offset + ((prob + 8) >> 4)
neg
add a,e ; A = prob_offset + prob - ((prob + 8) >> 4)
rra ; A = (bit<<4) + (prob>>4), CF=(prob & 8)
adc a,-16 ; A = (bit<<4) - 16 + ((prob + 8)>>4) ; -prob_offset = (bit<<4) - 16
sub e ; A = (bit<<4) - 16 + ((prob + 8)>>4) - prob ; = ((prob + 8)>>4) - prob_offset - prob
neg ; A = prob_offset + prob - ((prob + 8)>>4)
pop bc
ld (bc),a ; update probs[context_index]
add a,d ; bit=0: A = 23..249, D = 240 -> CF=1 || bit=1: D=0 -> CF=0
ccf ; resulting CF = bit restored
ld (bc),a ; probs[context_index] = prob_offset + prob - ((prob + 8) >> 4);
add a,d ; restore CF = bit (D = bit ? $FF : $00 && A > 0)
pop de
ret
@@ -287,12 +314,12 @@ 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)
.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
DISPLAY "upkr.unpack probs array placed at: ",/A,probs,",\tsize: ",/A,probs.c