XPCK

Filetype: Archive
File Extension(s): .pck, .xc, .xv, .xa, .xb, .xk, .xf, .xr
Signature: XPCK
Platform(s): Nintendo 3DS
Endianness: Little-endian
Used in: Yo-kai Watch 1, Yo-kai Watch 2, Yo-kai Watch Blasters, Yo-kai Watch 3, Yo-kai Watch Busters 2
Alignment: 4 Byte Alignment
String Encoding: ASCII

The XPCK file format is a generic flat archive (no directories) used to bundle related files together. The purpose of the XPCK in question can generally be inferred based on the file extension as shown below:

Extension	Description
.pck	A somewhat rare file extension that is completely generic in usage.
.xc	Used for model files containing many, many different properietary file formats.
.xv	Holds camera files, including CMR.bin and .cmr2.
.xa	Named XAnm, contains ANM resources: 2D textures, UVs, and other data for building UIs along with XQ scripts.
.xk	Named XSky, used to configure fog, sky, and related data. Includes SKY.bin, FOG.bin, SUB.bin, and .lgt files.
.xf	Known as XFont files, used to define custom fonts.
.xr	Generic resource bundle. Can contain 2D or 3D assets, though mostly 2D.
.xb	-

An XPCK file is composed of the header, followed by the file entry table, the (compressed!) name table and then the (4-byte aligned) file data section. All offsets are stored in units of 4 bytes (32-bit words). Meaning, to derive the offset in bytes you must multiply them by 4 or left-shift by 2 (<< 2). This however, will be mentioned for each applicable field.

Header

Offset	Size	Type	Name	Notes
0x00	4	char[4]	magic (XPCK)	Magic. Must always be equal to 0x4B435058 (ASCII representation of XPCK).
0x04	2	u16	fileCountAndType	fileCount = fileCountAndType & 0xFFF;, contentType = fileCountAndType >> 12;
0x06	2	u16	infoOffset	infoOffset << 2 defines the start of the File Entry table.
0x08	2	u16	nameTableOffset	nameTableOffset << 2 defines the start of the compressed Name Table.
0x0A	2	u16	dataOffset	Offset into the file data section in 32-bit words.
0x0C	2	u16	infoSize	Size of the File Entry Table section in 32-bit words; infoSize << 2 is equivalent to the size in bytes.
0x0E	2	u16	nameTableSize	Size of the compressed Name Table section in 32-bit words; nameTableSize << 2 is equivalent to the size in bytes.
0x10	4	u32	dataSize	Size of the file data section in 32-bit words; dataSize << 2 is equivalent to the size in bytes.

File Entry Table

The file entry table is located at the offset referenced by infoOffset << 2, with there being fileCount entries - each of size 0xC. Therefore the size (in bytes) can be calculated as: fileCount * 0xC. Aditionally, entries are sorted by their hash value in ascending order when written.

Structure

Offset	Size	Type	Name	Notes
0x00	4	u32	hash	CRC32-B of the filename string
0x04	2	u16	nameOffset	Offset relative to the start of the decompressed name table. Decompress the table before utilising this pointer.
0x06	2	u16	fileOffsetLower	-
0x08	2	u16	fileSizeLower	-
0x0A	1	u8	fileOffsetUpper	-
0x0B	1	u8	fileSizeUpper	-

Note that the fileOffset is relative to dataOffset and can be calculated using the following formula:

fileOffset = ((fileOffsetUpper << 16) | fileOffsetLower) << 2;

• fileSize calculation is similar but without the bit shift:

  fileSize = (fileSizeUpper << 16) | fileSizeLower;
  

Name Table

The Name Table is a compressed string table located at nameTableOffset << 2, of (compressed) size nameTableSize << 2 - it is composed of sequential null-terminated ASCII filenames.

Entry Ordering

Note that when writing, files must be sorted alphabetically by name when assigning offsets, just as the entries of the file entry table are sorted by hash.