Script to decompress .cx files found in Pokemon Rumble U

bMAL_decompress.py

import zlib
import sys
import struct

"""
.cx file header (0x14 in size):
    word[0] 0xe0000000 -> Magic, only the 0x0e is checked
    word[1] little endian value, uncompressed size
    word[2] 0x624d414c -> "bMAL" Magic
    word[3] little endian value, compressed size
    word[4] little endian crc32
"""

with open(sys.argv[1], "rb") as inf:
    with open(sys.argv[2], "wb") as outf:
        (magic0, decompressed_size, magic1, compressed_size, crc) = struct.unpack("<4sI4sII", inf.read(0x14))
        if magic0[0] != 0xe0 or magic1 != b"bMAL":
            raise Exception("Invalid magic values")

        compressed = inf.read()
        if len(compressed) != compressed_size:
            raise Exception("Invalid compressed size")

        decompressed = zlib.decompress(compressed)

        if len(decompressed) != decompressed_size:
            raise Exception("Invalid decompressed size")

        if zlib.crc32(decompressed) != crc:
            raise Exception("Checksum doesn't match")

        outf.write(decompressed)