; ----------------------------------------------------------------------------- ; ZX7 decoder by Einar Saukas & Urusergi ; "Turbo" version (88 bytes, 25% faster) ; ----------------------------------------------------------------------------- ; Parameters: ; HL = source address (compressed data) ; DE = destination address (decompressing) ; ----------------------------------------------------------------------------- ; Petite modification avec ajout des lignes ci-dessous + remplacement des $ par & ORG &9000 WRITE "turbo.bin" ;source address (compressed data) LD L,(IX+00) LD H,(IX+01) ;destination address (decompressing) LD E,(IX+02) LD D,(IX+03) dzx7_turbo: ld a, &80 dzx7t_copy_byte_loop: ldi ; copy literal byte dzx7t_main_loop: add a, a ; check next bit call z, dzx7t_load_bits ; no more bits left? jr nc, dzx7t_copy_byte_loop ; next bit indicates either literal or sequence ; determine number of bits used for length (Elias gamma coding) push de ld bc, 1 ld d, b dzx7t_len_size_loop: inc d add a, a ; check next bit call z, dzx7t_load_bits ; no more bits left? jr nc, dzx7t_len_size_loop jp dzx7t_len_value_start ; determine length dzx7t_len_value_loop: add a, a ; check next bit call z, dzx7t_load_bits ; no more bits left? rl c rl b jr c, dzx7t_exit ; check end marker dzx7t_len_value_start: dec d jr nz, dzx7t_len_value_loop inc bc ; adjust length ; determine offset ld e, (hl) ; load offset flag (1 bit) + offset value (7 bits) inc hl defb &cb, &33 ; opcode for undocumented instruction "SLL E" aka "SLS E" jr nc, dzx7t_offset_end ; if offset flag is set, load 4 extra bits add a, a ; check next bit call z, dzx7t_load_bits ; no more bits left? rl d ; insert first bit into D add a, a ; check next bit call z, dzx7t_load_bits ; no more bits left? rl d ; insert second bit into D add a, a ; check next bit call z, dzx7t_load_bits ; no more bits left? rl d ; insert third bit into D add a, a ; check next bit call z, dzx7t_load_bits ; no more bits left? ccf jr c, dzx7t_offset_end inc d ; equivalent to adding 128 to DE dzx7t_offset_end: rr e ; insert inverted fourth bit into E ; copy previous sequence ex (sp), hl ; store source, restore destination push hl ; store destination sbc hl, de ; HL = destination - offset - 1 pop de ; DE = destination ldir dzx7t_exit: pop hl ; restore source address (compressed data) jp nc, dzx7t_main_loop dzx7t_load_bits: ld a, (hl) ; load another group of 8 bits inc hl rla ret ; -----------------------------------------------------------------------------

======================= "ZX7" - by Einar Saukas ======================= "ZX7" is an optimal LZ77/LZSS data compressor for all platforms, including the ZX-Spectrum. Available implementations of standard LZ77/LZSS compression algorithm use either a "greedy" or "flexible parsing" strategy, that cannot always guarantee the best possible encoding. In comparison, "ZX7" provides a highly efficient compression algorithm that always generate perfectly optimal LZ77/LZSS encoding. Technically it means compressing within space and time O(n) only. ===== USAGE ===== To compress a file, use the command-line compressor as follows: zx7 Cobra.scr This will generate a compressed file called "Cobra.scr.zx7". Afterwards choose a decompressor routine in assembly Z80 for the ZX-Spectrum, according to your requirements for speed and size: * "Standard" routine: 69 bytes only * "Turbo" routine: 90 bytes, about 25% faster * "Mega" routine: 244 bytes, about 30% faster Finally compile the chosen decompressor routine and load the compressed file somewhere in memory. To decompress data, just call the routine specifying the source address of compressed data in HL and the target address in DE. For instance, if you compile the decompressor routine to address 65000, load "Cobra.scr.zx7" at address 51200, and want to decompress it directly to the screen, execute the following code: LD HL, 51200 ; source address (put "Cobra.scr.zx7" there) LD DE, 16384 ; target address (screen memory in this case) CALL 65000 ; decompress routine compiled at this address ======= LICENSE ======= The optimal C compressor is available under the "BSD-3" license. In practice, this is relevant only if you want to modify its source code and/or incorporate the compressor within your own products. Otherwise, if you just execute it to compress files, you can simply ignore these conditions. The Z80 assembly decompressors can be used freely within your own ZX-Spectrum programs, even for commercial releases. The only condition is that you must indicate somehow in your documentation that you have used "ZX7". ======= HISTORY ======= 2012-12-30: Initial release (with optimal compressor and Z80 decompressors) 2012-12-31: Minor changes to source code since it wasn't strictly ANSI C (thanks to Metalbrain!) 2013-01-03: Minor changes to data format increasing maximum offset by 6% thus improving compression, and some improvements in the "Standard" Z80 routine (thanks to Antonio Villena!) 2013-01-05: Further improvements in the "Standard" Z80 routine (thanks to Metalbrain!) 2013-02-25: Further improvements in the "Turbo" Z80 routine, released libraries for z88dk and Boriel's ZX BASIC. ======= CREDITS ======= The compressed file format is directly based (although slightly improved) on Team Bomba's Bitbuster - http://www.teambomba.net/bombaman/downloadd26a.html and Gasman's Bitbuster Extreme - www.west.co.tt/matt/speccy/apology/ Some of the size improvements used in "Standard" version were suggested by Antonio Villena and Metalbrain. The main speed improvement used in "Turbo" version was originally suggested by Urusergi for Magnus Lind's Exomizer - http://hem.bredband.net/magli143/exo/ The optimal LZ77/LZSS compress algorithm was invented by myself (Einar Saukas). To the best of my knowledge, there was no similar high-performance solution available. I thereby present this implementation as evidence of "prior art", thus preventing anyone from ever patenting it. Software patents are evil!!!