08it-crc.py

#!/usr/bin/env python3
import argparse

__title__ = "Xanavi CRC Tool"
__version__ = "0.1"
__author__ = "Gareth Bryan"
__license__ = "MIT"

FILETYPES = {
        #Type   Start, End, 2sComp
        "APP":      (4, -4, True),
        "DSP":      (4, -4, True),
        "CNFTBL":   (12, -4, False),
        # Many of the below seem to be pseudo-archives, TBD.
        #"BTFW":     (0, -4, True)
        #"BOT":      (,,) # BOT is a collection of files with multiple CRCs
        #"VCAN_SUB": (,,)
        #"DVD_MEC":  (,,)
        #"PROG":     (,,)
        #"DISP":     (,,)
        #"XMRADIO":  (,,)
        #"HDRADIO":  (,,)

}


def main(args):
    data = args.infile.read()
    file_crc = data[-4:]
    print(f"file crc   : {file_crc.hex()}")
    print("calculated : ", end="", flush=True)
    calc_crc = crc(args.filetype, data)
    print(calc_crc.hex())
    if args.update:
        if file_crc == calc_crc:
            print("crc already matches")
        else:
            with open(f"{args.infile.name}.bak", "wb") as backup:
                backup.write(data)
            args.infile.seek(len(data)-4)
            args.infile.write(calc_crc)
            print("crc updated")


def crc(filetype, data):
    start, end, twos = FILETYPES[filetype]
    crc = 0
    for chunk in (int.from_bytes(data[i:i+4], 'little') for i in range(start, len(data)-start+end, 4)):
        crc = 0xffffffff & (crc + chunk) + (0xffffffff & (crc + chunk) < crc)
    if twos:
        crc = 2**32 - crc
    return crc.to_bytes(4, 'little')


if __name__ == "__main__":
    parser = argparse.ArgumentParser(
        description="{} v{}".format(__title__, __version__)
    )
    parser.add_argument(
        "-t",
        help="File Type",
        choices=FILETYPES.keys(),
        dest="filetype"
    )
    parser.add_argument(
        "-u",
        help = "Update CRC",
        action="store_true",
        dest="update"
    )
    parser.add_argument(
        "infile",
        help="Input File",
        type=argparse.FileType("r+b"),
    )
    args = parser.parse_args()
    main(args)