Wikifang:Telefang 1 Translation Patch/NatsumeGB compression

NatsumeGB compression is the compression algorithm used in numerous Game Boy Natsume games, namely, at least Telefang and Medarot. It is a modified implementation of the LZ77 algorithm, which works by referencing previously decompressed data using length-distance pairs. Wikipedia has a good description of the algorithm.

NatsumeGB was formerly called Malias compression after Malias, the person who wrote the first decompresser.

Implementation of the NatsumeGB compression in pseudocode:

compressed = readbyte()
if compressed != 0x00:
    total = readshort()             # Total length of the graphics
    while bytes < total:            # bytes is number of bytes decompressed
        modes = readshort()         # Contains modes for the next 10 bytes
        for mode in bits(modes):
            if mode == 0x1:         # Copy mode
                loc = -(readshort() & 0x7ff)
                num = lastbyte >> 3 & 0x1f + 0x03
                loc += bytes-1
                do num times:
                    data += data[loc]
                    loc += 1
            else:                   # Insert mode
                data += readbyte()

Games that use the compression

• Keitai Denjuu Telefang
• Medarot 1
• Medarot 2
• Medarot 3
• Medarot 4 (assumed)
• Medarot 5 (assumed)
• Croc 2

Decompression tools

• Malias' Telefang Tools can decompress and recompress the graphics with ease, provided locations.
• punika is a simple implementation in Python which decompresses all compressed graphics at once, working off tables in the ROM.