Difference between revisions of "YAZ0 (File Format)"

Revision as of 20:47, 6 April 2011

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

Data structure

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.

Examples

Decompression

Compression

@@ Line 31: / Line 31: @@
 === Data Groups ===
+The complete compressed data is organized in '''data groups'''. Each data group consists of 1 sequence header byte an 8 '''data sequences''':
+{| class="wikitable"
+|-
+! 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.
+{| class="wikitable"
+|-
+! 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.
 == Examples ==