qd2fds.py

#!/usr/bin/env python3
"""
Converts between QD and FDS disk images
"""
import struct


def create_fds_header(side_count):
    return b"FDS\x1A" + bytes([side_count & 0xFF]) + bytes(11)


def fds_crc(data):
    # http://forums.nesdev.com/viewtopic.php?p=194867
    # Do not include any existing checksum, not even the blank checksums 00 00 or FF FF.
    # The formula will automatically count 2 0x00 bytes without the programmer adding them manually.
    # Also, do not include the gap terminator (0x80) in the data.
    # If you wish to do so, change sum to 0x0000.
    s = 0x8000
    for byte in data + bytes(2):
        s |= byte << 16
        for _ in range(8):
            if (s & 1):
                s ^= 0x8408 << 1
            s >>= 1
    return s


def convert_to_fds(disk, null):
    """
    Convert a .qd to .fds
    """
    del disk[0x38:0x3A]  # 01 block chksum
    # fn = disk[0x39]  # get num of files from 02 block
    pos = 0x3A
    del disk[pos: pos + 2]  # 02 block chksum
    try:
        while disk[pos] == 3:  # if there's any more files, like in Doki Doki Panic
            print(f"{pos:05X}\t{disk[pos + 0x3:pos + 0xB].decode('latin_1')}")
            filesize, = struct.unpack('<H', disk[pos + 0xD: pos + 0xF])
            del disk[pos + 0x10: pos + 0x12]  # 03 block chksum
            pos = pos + 0x10 + 1 + filesize
            del disk[pos: pos + 2]  # 04 block chksum
    except IndexError:
        pass

    if len(disk) > 65500:
        disk = disk[:65500]
    else:
        disk = disk.ljust(65500, b"\0")

    return disk


def convert_to_qd(disk, null):
    """
    Convert a .fds to .qd
    """
    def insert_crc(start, end, null):
        if not null:
            crc = fds_crc(disk[start:end])
            disk.insert(end + 0, crc & 0xFF)
            disk.insert(end + 1, crc >> 0x8)
        else:
            disk.insert(end + 0, 0)
            disk.insert(end + 1, 0)

    if disk[0] != 0x01:
        return bytearray()

    insert_crc(0, 0x38, null)  # 01 block chksum
    # fn = disk[0x3B]  # get num of files from 02 block
    pos = 0x3A
    insert_crc(pos, pos + 2, null)  # 02 block chksum
    pos = 0x3E
    try:
        while disk[pos] == 3:  # if there's any more files, like in Doki Doki Panic
            print(disk[pos + 0x3: pos + 0xB].decode('latin_1'))
            filesize, = struct.unpack('<H', disk[pos + 0xD: pos + 0xF])
            insert_crc(pos, pos + 0x10, null)  # 03 block chksum
            pos += 0x10 + 2
            insert_crc(pos, pos + 1 + filesize, null)  # 04 block chksum
            pos += 1 + filesize + 2
    except IndexError:
        pass

    if len(disk) > 0x10000:
        disk = disk[:0x10000]
    else:
        disk = disk.ljust(0x10000, b"\0")

    return disk


if __name__ == '__main__':
    import sys
    import argparse
    from pathlib import Path

    parser = argparse.ArgumentParser(description='Converts between QD and FDS disk images')
    parser.add_argument('rom', metavar='ROM', help='QD or FDS file')
    parser.add_argument('-o', '--output')
    parser.add_argument('-f', '--fds-header', action='store_true', help='add FDS header')
    parser.add_argument('-n', '--null-checksum', action='store_true', help='use null bytes instead of calculated checksum (like in some VC games)')
    args = parser.parse_args()

    path = Path(args.rom)
    try:
        size = path.stat().st_size
    except FileNotFoundError as err:
        print("File Not Found: {0}".format(err))
        sys.exit(1)
    if not path.is_file():
        print("Error: It's not file: '{0}'".format(args.rom))
        sys.exit(1)

    side_size = 0
    start_pos = 0
    convert_func = None
    ext = ''
    if size % 0x10000 == 0:
        side_size = 0x10000
        convert_func = convert_to_fds
        ext = '.fds'
    elif size % 65500 == 0 or size % 65500 == 16:
        side_size = 65500
        start_pos = size % 65500
        convert_func = convert_to_qd
        ext = '.qd'

    if convert_func:
        in_bytes = bytearray(path.read_bytes())
        out_bytes = bytearray()
        if ext == '.fds' and args.fds_header:
            out_bytes += create_fds_header(size // side_size)

        for i in range(start_pos, size, side_size):
            out_bytes += convert_func(in_bytes[i: i + side_size], null=args.null_checksum)

        path = path.with_suffix(ext)
        if args.output:
            path = Path(args.output)
        path.write_bytes(out_bytes)

Very nice and usefull tool, thanks a lot.
Sadly it doesn't work if the FDS file has a header.
Can you add the possibility to convert both, with and without header ?
Or adding an error message if there're problems because of the header.
That would be AWESOME 😃 👯‍♀️

This is great, but I keep encountering an issue with Super Mario Bros The Lost Levels. I have a QD rom of that game that matches the checksums on no-intro:
https://datomatic.no-intro.org/?page=show_record&s=31&n=0333
But the resulting FDS rom doesn't match the checksums found here:
https://datomatic.no-intro.org/?page=show_record&s=31&n=0297
Something similar is happening to Bubble Bobble, but from FDS to QD.

A while back, I added Famicom Disk System rom extraction to this project:
https://github.com/wheatevo/wiiu-vc-extractor
I realized that the Wii U VC used QD roms, so I converted this script to C# in order for the extracted roms to be playable in most emulators, but I had to add a patch for Lost Levels to match the entry on no-intro.

Do you have any idea why these converted roms don't match the known dumps?

@TBirdSoars

This is great, but I keep encountering an issue with Super Mario Bros The Lost Levels. I have a QD rom of that game that matches the checksums on no-intro:
https://datomatic.no-intro.org/?page=show_record&s=31&n=0333
But the resulting FDS rom doesn't match the checksums found here:
https://datomatic.no-intro.org/?page=show_record&s=31&n=0297

This is because the GC/Wii/U version is a derivative of the non-DV2 version (https://datomatic.no-intro.org/index.php?page=show_record&s=31&n=0120) with 3 single byte patches. The resulting FDS file of this version should have the SHA1 hash b2dbc55efcae77abad6207b802c0a76d7a47ed0d.

Something similar is happening to Bubble Bobble, but from FDS to QD.

I can only presume this is due to the same thing as the VC versions are prepatched ROMs

Thanks for the quick reply!
Interesting. That SHA1 hash does in fact match the Lost Levels QD rom I have. It would make sense then that my Bubble Bobble QD wouldn't match the Wii U QD dump, since my FDS rom matches this one:
https://datomatic.no-intro.org/?page=show_record&s=31&n=0208