Difference between revisions of "YAZ0 (File Format)"
Line 109: | Line 109: | ||
return ERROR("Corrupted data!\n"); | return ERROR("Corrupted data!\n"); | ||
− | + | while ( n-- > 0 ) | |
− | + | *dest++ = *copy_src++; | |
} | } | ||
code <<= 1; | code <<= 1; |
Revision as of 21:04, 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
- GNU C example
const u8 * src = // pointer to start of source const u8 * src_end = // pointer to end of source (last byte +1) u8 * dest = // pointer to start of destination u8 * dest_end = // pointer to end of destination (last byte +1) u8 code = 0; // code ... int code_len = 0; // ... and code_len used to manage groups while ( src < src_end && dest < dest_end ) { if (!code_len--) { code = *src++; code_len = 7; } if ( code & 0x80 ) { // copy 1 byte direct *dest++ = *src++; } else { // rle part const u8 b1 = *src++; const u8 b2 = *src++; const u8 * copy_src = dest - ( ( ( b1 & 0x0f ) << 8 ) | b2 ) - 1; ASSERT( copy_src >= szs->data ); int n = b1 >> 4; if (!n) n = *src++ + 0x12; else n += 2; ASSERT( n >= 3 && n <= 0x111 ); ASSERT( copy_src + n <= szs->data + szs->size ); if ( dest + n > dest_end ) return ERROR("Corrupted data!\n"); while ( n-- > 0 ) *dest++ = *copy_src++; } code <<= 1; } ASSERT( src <= src_end ); ASSERT( dest <= dest_end );
This code example is taken from Wiimms SZS Tools: SVN repository lib-szs.c line 159