ROM Hack .arc File extension

[Gryphon93]

I've unpacked Time Hollow and found out that almost everything is packed in .arc-files (archives). I'm wondering if it exists any tools to extract the files from the archive, or if it at least exists somekind of reference/documentation?

Now, before you say "Use NARCTool" I would like to say that this kind of .arc-format isn't the same as the other .arc-format for DS. I've tried to use NARCTool, but without any luck. I've also tried to use some tools made for the GC/Wii .arc-format, but (as I excepted) they didn't work either. Well, if there's no reference/documentation nor tools to extract the archive, please help me find out how to extract this kind of .arc-files. I've already "researched" a little by myself. This is what I've come up with so far:

Reference/Documentation (Not complete and not sure that it's correct):

OffsetÂÂÂÂÂÂÂÂSize ÂÂÂÂDescription
0x00000000ÂÂÂÂ0x4ÂÂÂÂÂÂÂÂ"Magic ID"ÂÂÂÂÂÂÂÂ// Always "ARCH"
0x00000004ÂÂÂÂ0x4ÂÂÂÂÂÂÂÂNo. of Files
0x00000008ÂÂÂÂ0x4ÂÂÂÂÂÂÂÂName Table Offset
0x0000000cÂÂÂÂ0x4ÂÂÂÂÂÂÂÂINFO-OffsetÂÂÂÂ// Not sure if this is part is called INFO, but that's what I call it for now
0x00000010ÂÂÂÂ0x4ÂÂÂÂÂÂÂÂFILE-OffsetÂÂÂÂ
0x00000014ÂÂÂÂ0x4ÂÂÂÂÂÂÂÂHEADER-size (in bytes)
0x00000020ÂÂÂÂ0x4ÂÂÂÂÂÂÂÂFile size (?)
0x00000024ÂÂÂÂ0x4ÂÂÂÂÂÂÂÂNo. of Files (again?)

And here is a small dump from the program I made to read the .arc-files:

D00_00_00.arcÂÂÂÂ // Found in data\bg\digging
ARCH
11
32
208
384
432
176
11
// This is NOT in Hex

You can find the .arc-files in Time Hollow. Almost everything is in .arc-archives.

All help is appreciated! Thanks in advance!

[EDIT] Updated the "reference". Please help me complete it!
[EDIT 2] Thanks to Barubary for his help finding out everything about the format!

 

[Gryphon93]

Sorry for double posting, but I really want/need help... I want help with finding out if the file data is compressed (which I belive it is) and what kind of compression method that's used (maybe somekind of LZ-compression?). I hope someone can help me. I really want the files in these archives. This is the first time I'm trying to something like this. I mean, understand a file format, make the reference myself and so on. Please, ALL help is appreciated!

 

[DarthNemesis]

LZ-compressed files can be identified by a starting byte of 0x10 or 0x11 followed by a 3 byte length and a flag byte (the first one should always be 00) before the actual file data begins. If you see a signature at the very start of the file rather than 5 bytes in, it's not likely to be compressed (but if it's an archive, the individual files inside it could still be compressed once you've extracted them).

 

[Gryphon93]

Hm... Alright... I think I got that. So the archives are probably not compressed (if I've understood the last part of your post correctly), since the first bytes in the whole archive are ARCH (HEX: 41 52 43 48). Well, I've probably misunderstood what you said, but hopefully the files aren't compressed. (It will be much easier that way, I think)

 

[Barubary]

Indeed, the archives themselves are not compressed, but the files inside are (or otherwise encrypted).


This seems to be the format of the ARCH-files;

typedef struct {
char[4] magicHeader; // 'ARCH'
u32 numFiles;
u32 nameTableOffset;
u32 fatOffset;
u32 nameIndexOffset;
u32 dataOffset;
} ARCHHeader

typedef struct {
u32 sectionSize;
u32 numNames; // practically always the same as numFiles
char** names; // 'numNames' 0-terminated strings
} NameTable

typedef struct {
u32 fileLength;
u32 unknown1; // flags? seem to be (almost) the same per filetype
u32 fileStart; // relative to dataStart
u16 nameOffset; // offset of name in NameTable. relative to start of NameTable section
u16 unknown2; // ??? constant 1? amount of similar files directly following afterwards perhaps?
} FileAllocation

typedef struct {
FileAllocation[numFiles] fat;
} FileAllocationTable

typedef struct {
u16 index;
u16 nameOffset;
} NameIndexEntry
// from what I've seen, this section has little added value. It seems to bind file numbers with their names, but that's already done in the FAT.
// the 'index'th FileAllocation in the FAT has the same nameOffset as defined here

typedef struct {
NameIndexEntry[numFiles] nit;
} NameIndexTable // (I'm just calling it something that sounds like what the section seems to be)

However, I've no idea of the compression/encryption technique used in the files inside.

 

[Gryphon93]

Wow! Thanks a lot Barubary! This will be VERY useful! Thank you! I got stuck at the FILE-part. I could only figure out the HEADER (almost)...

[EDIT] Do you think I can use NARCTool's source when I make the ARCTool? I mean, just use the functions and stuff, but changing the header-file (and the other things that have to be changed). Or is it possibly easier to make the whole thing from scratch? I'm planning to make it in Ruby.

 

[Gryphon93]

Sorry for bringing my "old" topic back up, but I just want to ask you (again...) for some help.

I'm working on a utility that'll be able to extraxt and (hopefully) pack .arc-files. What I want help with is the few things that are still unknown about the ARCH-format. As you can see in Barubary's code, there's some things that we don't know what they are for and what they mean. I hope someone can help me find out what these things are and tell me. It may be something that's needed to extract/pack the .arc-files.

Thanks a lot in advance! I really appreciate all your help! Thanks for all the help you've already given me!

[EDIT] I'm almost there! I hope it isn't much left to do before I'm able to extract the .arc-files. I just have to read the data and save it as files.

 

[Gryphon93]

Alright, sorry for triple-posting... Really, sorry. I just want to report my progress.

I'm now able to extract the files from the archives, but now I've to find out what kind of compression-method that's used.

Again, I would like to ask for your assistance. I want to know what compression-method that's used, and to help you a bit I'll post some files here for you.

Download link (extracted_files.rar)

I hope you're able to help me. It's the last thing I need to finish the extract-function.

 

[Marvin Dalkiri]

Well, I've checked your files, and as far as I know, these aren't any of the DS standard compressions.

However, these could be some sort of flagless LZSS, or something like that.

I'm gonna check again these files later when I get home, and see what I can find uot about them.

 

[Gryphon93]

Thanks a lot! Just hearing that you've checked the files are great news for me! I'm also checking them. I comparing the files with other files with the same extensions to see if I can figure something out.

Oh, something I forgot to say earlier. It seems like the 4 first bytes are (almost) always FE 7F. Mabye that can help anything.

 

[DarthNemesis]

The last 2 bytes before the file signature (RLCN, RCGN, etc.) hold the length of the compressed data.

 

[Gryphon93]

Nice! Thanks for the information, Darth Nemesis. I really appreciate it. As soon as I know what kind of compression method that's used, I'll be able to finish the extract-function and begin to work on the packing-function.

 

[Xerawels]

Hey Gryphon ! Do your researches advance ? Me too, I would really like to be able to change the .arc files of Time Hollow !

 

[azure0wind]

Hey Gryphon ! Do your researches advance ? Me too, I would really like to be able to change the .arc files of Time Hollow !

off topic

anyway now, what do you want to help with?

 

[Midou23000]

What about ARC files from 3Ds carts like Super street fighter 4 3D edition i decrypt the ROM but i can open the ARC extension for some mods ^^ please help me

 

[Februarysn0w]

What about ARC files from 3Ds carts like Super street fighter 4 3D edition i decrypt the ROM but i can open the ARC extension for some mods ^^ please help me

Try this ARC tool. I successfully unpacked Arc files that come with MH4G (JPN). Just drag and drop your file to "pc-re6-extract.bat" or "pc-re5-extract.bat".

 

[Midou23000]

thx ^^

 

[Midou23000]

not work for me

 

[Midou23000]

https://mega.co.nz/#!IJkHyAJD!XzmDoH_wiKy9eJl1G7-L26x-5LSrxSin9KucPLZ0Gag this is the files if you like to try ^^

 

[Kelebek]

https://mega.co.nz/#!IJkHyAJD!XzmDoH_wiKy9eJl1G7-L26x-5LSrxSin9KucPLZ0Gag this is the files if you like to try ^^

http://pastebin.com/Kz2MS34Q - Python 2.7. Run it from the folder with the .arc files in.