Re: Checksums (was re: 8r fonts)

["Berthold K.P. Horn" <bkph@ai.mit.edu>]

Hi:

J"org writes:

   If one can encode about six letters in the checksum, we should think very 
   carefull about which information should be encoded there. IMHO, encoding 
   the font encoding is a particularly bad idea, since the tfm file format 
   already has a place for a string called CODINGSCHEME.

Which is useless, since it is not carried over to the DVI file.  You
can hide all sorts of things in the TFM file, but it does no good
unless it gets put in the DVI file.  And the only thing that is, is
the CheckSum.

   This string should be as precise as possible and can of course be examined 
   by dvi drivers. It can -- with pk fonts at least -- also be compared to the 
   special information stored there. METAFONT *always* put the codingscheme 
   special into the gf file, not only with mode defined specials.

   There is other information which one likes to check (e.g. Version numbers)
   and which is otherwise not accessible through the tfm file.

You can only squezze that much into 6 characters.  And the encoding is
the most important by a long shot.  This was not an issue hen TeX started
since all CM fonts have fixed-hard wired encoding.  Today it is a *big*
issue.  Just like missing characters were not an issue in the good 
old days because CM fonts were `full'  now it is a big deal.  We need
to give users tools to help debug encoding problems and  missing character 
problems (which result from encoding problems).  

   --J"org Knappen.