Compression

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.

Terranigma Compression Format

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.