Date   : Sun, 26 Feb 2006 14:26:49 +0000
From   : jgh@... (Jonathan Graham Harston)
Subject: DFS Catalogue sanity check

jgh@... (Jonathan Graham Harston) wrote:
> > Then sanity-check file offsets + lengths and make sure the catalogue is
> > ordered (along with checking for a second Watford - or Torch - catalogue
at
> 
> A sanity check will quickly eliminate a Torch catalogue, as it
> looks nothing like a sane DFS catalogue.
 
Some simple sanity checks to eliminate non-DFS/WDFS/HDFS disk
catalogues. In all cases, assuming a "clean" DFS catalogue, and
not one that has been modified, for instance, as part of copy
protection by "poking" invalid characters into the title or
filenames, etc.
 
&105 - (Number of catalogue entries)*8. So, b0-b1-b2 will always
be zero. If b0-b1-b2<>%000, then not DFS.
 
&000-&007 - Disk title. All bytes will be >=&20 or &00. If any
byte &01..&20, then not DFS.
 
&100-&103 - Disk title. All bytes will be >=&20 or &00. If any
byte &01..&20, then not DFS.
 
Catalogue entries. For each entry up to the total specified in
&106:
 
&008+x: Ignoring b7, all eight bytes in the filename will be
&20..&7E. If any byte is &00-&1F or &7F, then not DFS.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
BBC IDE Hard Drive Interface - http://mdfs.net/Info/Comp/BBC/IDE