Compression
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Terranigma uses a compression for most of the data.
Format
Compressed data always starts with a 4 byte header:
| Offset | Length | Description |
|---|---|---|
| 0 | 1 | Chunk Counter ??, always 0 (not used in the game) |
| 1 | 2 | Uncompressed data size (LE) |
| 3 | 1 | First byte of uncompressed data |
After that follows the compressed data. It consists of data bytes intersparsed with a control code bitstream, both use MSB first (BE) encoding. Data bytes are always aligned at byte boundary. The control code stream is fit in between the data bytes so that a new cc byte is only placed when a bit needs to be used and the previous cc byte is full.
| cc | cc | cc | cc | 8 bit | 5 bit | 3 bit | 8 bit | Description |
|---|---|---|---|---|---|---|---|---|
| 1 | - | Literal | - | Literal Byte | ||||
| 0 | 1 | - | Offset | Length != 0 | - | Copy Length+2 bytes from next_output_pos-0x2000+offset to the output | ||
| 0 | Length != 0 | Copy Length+1 bytes from next_output_pos-0x2000+offset to the output | ||||||
| 0 | End of Data (usually in this case Offset is also 0) | |||||||
| 0 | Length | Offset | - | Copy Length+2 bytes from next_output_pos-0x100+offset to the output | ||||
In the table, each cc stands for a control code bit. The second data byte is divided into 5+3 bits for mode 01.
Tool
Crediar re'ed the decompression from the code and translated it to C code.
You can download a tool with the source to decompress data from any given offset here.