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