Re: [MI400] Analyzing SAV save files from a PC

["James H. H. Lampert" <jamesl@xxxxxxxxxxx>]

Fellow programmers:

The first thing you need to keep in mind is that while the first
QSRDSSPC.1 record starts in one of only a few standard places, and that
the displacements between them are in 528-byte records, the
displacements to the DIR and LNK structure, &c., are all in bytes, and
they are all MODULO the 26 bytes of stuff at the ends of the records,
and that you must assume that ANYTHING can span a record boundary.

Therefore, before you can do anything else with an IFS save file, you
absolutely MUST be able to both read, and calculate byte displacements,
across any arbitrary number of record boundaries, skipping those bytes.
Proceed no further until you can do that.

As with any save file, the first step is to find the first QSRDSSPC.1
record, and the save type byte. 14 hex (20 decimal) indicates SAV. Get
the record displacement to the next QSRDSSPC.1 record, and the byte
displacement to the DIR structure.

Set the root node of your tree to the directory name, then start picking
your way through the LNK structures, adding child nodes to your root
node as you go along. (Incidentally, the 6th displacement points to a
structure that includes the object type.) Every time you hit a link that
is a *DIR, don't just add it to the root node; save it someplace you can
grab it by its pathname. (Why does corned beef suddenly come to mind?)
Also, you should figure out some way to mark the node so that when your
tree is rendered, it gets a "folder" icon, rather than a "file" icon,
even if it's empty.

When you've run out of LNK structures, jump to the next QSRDSSPC.1
record, and repeat the process, EXCEPT that instead of using the
directory path given in the DIR structure to name a root node, you use
it to retrieve the node for the corresponding *DIR.

Just keep repeating the process until you run out of QSRDSSPC.1 records,
and you'll have a tree representing the contents of your save file.

That's the algorithm. Implementing it is  the <female canid> (sort of
the same level of difficulty as Sheriff Bart inventing the candy-gram
["Mongo like candy!"])

-- 
James H. H. Lampert
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