MegaLZ.bas
megaLZDepack.bas
This routine takes a block of data compressed with the MegaLZ compression algorithm at SOURCE location and decompresses it to DESTINATIOn location. You should probably save compressed files as direct binaries, and use asm mode incbin commands to include the binary into your project.
THIS METHOD IS NOW INCLUDED IN THE ZX BASIC EXTERNAL LIBRARY (the library folder),
so can and should be included with #include <megalz.bas> for the latest code.
SUB megaLZDepack (source as uInteger, dest as uInteger)
ASM
LD E,(IX+6)
LD D,(IX+7)
;Z80 depacker for megalz V4 packed files (C) fyrex^mhm
; DESCRIPTION:
;
; Depacker is fully relocatable, not self-modifying,
;it's length is 110 bytes starting from DEC40.
;Register usage: AF,AF',BC,DE,HL. Must be CALL'ed, return is done by RET.
;Provide extra stack location for store 2 bytes (1 word). Depacker does not
;disable or enable interrupts, as well as could be interrupted at any time
;(no f*cking wicked stack usage :).
; USAGE:
;
; - put depacker anywhere you want,
; - put starting address of packed block in HL,
; - put location where you want data to be depacked in DE,
; (much like LDIR command, but without BC)
; - make CALL to depacker (DEC40).
; - enjoy! ;)
; PRECAUTIONS:
;
; Be very careful if packed and depacked blocks coincide somewhere in memory.
;Here are some advices:
;
; 1. put packed block to the highest addresses possible.
; Best if last byte of packed block has address #FFFF.
;
; 2. Leave some gap between ends of packed and depacked block.
; For example, last byte of depacked block at #FF00,
; last byte of packed block at #FFFF.
;
; 3. Place nonpackable data to the end of block.
;
; 4. Always check whether depacking occurs OK and neither corrupts depacked data
; nor hangs computer.
;
;DEC40
LD A,80h
EX AF,AF'
MS: LDI
M0: LD BC,2FFh
M1: EX AF,AF'
M1X: ADD A,A
JR NZ,M2
LD A,(HL)
INC HL
RLA
M2: RL C
JR NC,M1X
EX AF,AF'
DJNZ X2
LD A,2
SRA C
JR C,N1
INC A
INC C
JR Z,N2
LD BC,33Fh
JR M1
X2: DJNZ X3
SRL C
JR C,MS
INC B
JR M1
X6:
ADD A,C
N2:
LD BC,4FFh
JR M1
N1:
INC C
JR NZ,M4
EX AF,AF'
INC B
N5: RR C
JP C, END_DEC40
RL B
ADD A,A
JR NZ,N6
LD A,(HL)
INC HL
RLA
N6: JR NC,N5
EX AF,AF'
ADD A,B
LD B,6
JR M1
X3:
DJNZ X4
LD A,1
JR M3
X4: DJNZ X5
INC C
JR NZ,M4
LD BC,51Fh
JR M1
X5:
DJNZ X6
LD B,C
M4: LD C,(HL)
INC HL
M3: DEC B
PUSH HL
LD L,C
LD H,B
ADD HL,DE
LD C,A
LD B,0
LDIR
POP HL
JR M0
END_DEC40:
END ASM
END SUB
Usage
Example: