C.0.1 Old GNU Format

The format introduced some time around 1990 (v. 1.09). It was designed on top of standard ustar headers in such an unfortunate way that some of its fields overwrote fields required by POSIX.

An old GNU sparse header is designated by type ‘S’ (GNUTYPE_SPARSE) and has the following layout:

Offset	Size	Name	Data type	Contents
0	345		N/A	Not used.
345	12	atime	Number	atime of the file.
357	12	ctime	Number	ctime of the file .
369	12	offset	Number	For multivolume archives: the offset of the start of this volume.
381	4		N/A	Not used.
385	1		N/A	Not used.
386	96	sp	sparse_header	(4 entries) File map.
482	1	isextended	Bool	1 if an extension sparse header follows, 0 otherwise.
483	12	realsize	Number	Real size of the file.

Each of sparse_header object at offset 386 describes a single data chunk. It has the following structure:

Offset	Size	Data type	Contents
0	12	Number	Offset of the beginning of the chunk.
12	12	Number	Size of the chunk.

If the member contains more than four chunks, the isextended field of the header has the value 1 and the main header is followed by one or more extension headers. Each such header has the following structure:

Offset	Size	Name	Data type	Contents
0	21	sp	sparse_header	(21 entires) File map.
504	1	isextended	Bool	1 if an extension sparse header follows, or 0 otherwise.

A header with isextended=0 ends the map.