YAZ0 (File Format)

Yaz0 is a run length encoding (RLE compression) method. In Mario Kart Wii most of the SZS files are Yaz0 compressed U8 files.

Header

The header of a Yaz0 file is always 16 bytes long. All numeric values stored as big endian values.

Offset	Type	Description
0x00	char[4]	always "Yaz0"
0x04	u32	size of the umompressed data
0x08	char[16]	always zero (padding)

GNU C example

typedef struct yaz0_header_t
{
    char	magic[4];		// always "Yaz0"
    be32_t	uncompressed_size;	// total size of uncompressed data
    char	padding[8];		// always 0?
}
__attribute__ ((packed)) yaz0_header_t;

Data Groups

The complete compressed data is organized in data groups. Each data group consists of 1 sequence header byte an 8 data sequences:

N	Size	Description
1	1	the sequence header byte
8	1-3	8 data sequences

Each bit of the sequence header corespondents to one sequence:

• The MSB (most significant bit, 0x80) corespondents to sequence 1
• The LSB (lowest significant bit, 0x01) corespondents to sequence 8

A set bit (=1) in the sequence header means, that the sequence is 1 exact 1 byte long. This byte must be copied to the output stream 1:1. A cleared bit (=0) defines, that the sequence is 2 or 3 bytes long interpreted as a back reference to already decompressed data that must be copied.

Size	1.B	2.B	3.B	Comment
2	NR	RR	-	N=1..f, SIZE=N+2
3	0R	RR	NN	N=00..ff, SIZE=N+0x12

• RRR is a value between 0x000 and 0xfff. Go back RRR+1 bytes in the output stream to find the start of the data to be copied.
• SIZE is the number of bytes to be copied.

Decoding data groups and data sequences are done until the end of the destination data is reached.