Quick/dirty WAD4 format idea.

Header {
	FOURCC	magic;		//00: 'WAD4'
	U32		numlumps;	//04: Number of lumps in the directory.
	U32		diroffs;	//08: Offset of Directory
	U32		hashoffs;	//0C: Offset of Directory Hash.
	U32		bmpoffs;	//10: Offset of Allocation Bitmap.
	U32		resv3;		//14: Reserved
	U32		resv4;		//18: Reserved
	U32		resv5;		//1C: Reserved
	//...
}

An allocation bitmap may be present to allow basic Read/Write access.
This format will focus primarily on a read-only use-case though.


DirEntW4 {
	U32		offs;		//00: offset of lump data
	U32		csize;		//04: compressed size of lump
	U32		dsize;		//08: uncompressed size of lump
	BYTE	ety;		//0C: entry type
	BYTE	cmp;		//0D: compression method
	U16		chain;		//0E: lump chain (hash)
	U16		dirid;		//10: Directory ID (Parent Directory)
	U16		dirnext;	//12: Next in Directory
	U16		uid;		//14: UID
	U16		gid;		//16: GID
	U16		mode;		//18: Mode Flags (---Srwxrwxrwx)
	U16		hibits;		//1A: Some extra bits
	U32		mtime;		//1C: File timestamp
	BYTE	name[32];	//20: name
}

Offsets will be scaled by 64 bytes.
Thus, the maximum theoretical WAD4 image size will be 256GB.

ety:
* 0: Normal File / Unused Dirent
* 1: Directory
* 2: Symlink

cmp:
* 0: Uncompressed
* 1: Fragmented File (Large File)
* 2: Merged / Packed File (Small File)
* 3: RP2 Compressed
* 4: LZ4 Compressed

hibits:
* ( 3:0): chain-hi
* ( 7:4): dirnext-hi
* (11:8): mtime-hi
** Extend timestamp to 3062.