(Recovered from SMWiki, improvements are welcome.)
Latest revision as of 23:30, 9 November 2019
LZ5 or LC_LZ5, as named by Lunar Compress, is a lossless data compression format, used by Super Mario Kart to compress graphics and other data. The LZ5 compression format is a slight enhancement of the LZ2 compression format, due to new commands.
The compressed data consists of "chunks", each with a header:
bits 76543210 CCCLLLLL CCC: Command bits LLLLL: Length
If the header byte is $FF, the end of the compressed data has been reached, and decompression will be aborted.
The commands mostly remain their LC_LZ2 commands. However, there are new commands too. Here is a list of commands bits which the LC_LZ5 decompression function can use during the decompression:
000 "Direct Copy" Followed by (L+1) bytes of data 001 "Byte Fill" Followed by one byte to be repeated (L+1) times 010 "Word Fill" Followed by two bytes. Output first byte, then second, then first, then second, etc. until (L+1) bytes has been outputted 011 "Increasing Fill" Followed by one byte to be repeated (L+1) times, but the byte is increased by 1 after each write 100 "Repeat" Followed by a word (little-endian) containing address relative to the output buffer's first byte to copy (L+1) bytes from. Basically it's this math: (Output buffer offset + word value) 101 "XOR Repeat" Same concept as above, except all the copied bytes are getting XOR'd by the value $FF. 110 "Negative Repeat", followed by a byte subtracted by the CURRENT index to the output buffer, to copy (L+1) bytes from. Basically it's this math: (Output buffer offset's index - byte value) 111 "Long length" This command has got a two-byte header: 111CCCLL LLLLLLLL CCC: Real command LLLLLLLLLL: Length
Long Length-exclusive command 111 "Negative XOR repeat" Same concept as "Negative Repeat", except all the copied bytes are getting XOR'd by the value $FF.
Seeing that the long length command uses ten bits for its length, the maximum length is 1024 bytes/1kB, while the normal length is 32 bytes.
You can use the LZ5 compression to mainly compress graphics and data. Technically you can compress anything with this format.