Rinia (1/14/04)

Rinia is a tool for embedding CRCs in text files.  No need to assign
strange file names or package .SFVs with your files!  Rinia will
insert a human-readable checksum string in the text itself!  ^_^

0. Usage                                                                   `

   rinia <infile> <layout> <outfile>

   All three arguments may reference the same file.  All files is
   assumed to be of ASCII character set.

1. Input                                                                   %

   Any file larger than 8 bytes is valid.  Upper limit on file size is
   limited by memory.

   If input file can't be loaded for any reason, Rinia will say "bad
   input" and exit immediately.

2. Layout                                                                  _

   The layout file contains a map of where Rinia can patch.  The
   content consists of marker characters (where Rinia is allowed to
   change in the original text) and other characters (where the
   original text will stay as is).  Rinia will select the marker
   character using these heuristics:

   1. Ignore all space/control/extended characters.
   2. Select characters that appeared 8 times in a row.
   3. Of those selected characters, pick one with the lowest
      frequency.

   One way to create the layout file is to make a copy of the original
   file, replace where you want Rinia to match with a rare character,
   then replace the remaining ones with space.  Often it's possible to
   write the original file in such a way that it can be used as a
   layout.

   Example file/layout:

      file:                layout:
         crc = ########       ... . XXXXXXXX
         patch = ######       ..... . XXXXXX
         other text here      ..... .... ....

   And Rinia may generate a file similar to this:

      crc = 1bad73cf
      patch = #FR-QQ
      other text here

   Note that the original file by itself is a valid layout file, since
   Rinia will recognize that only # marks enough space to hold the
   checksum, and has the lowest frequency.

   If layout file can't be used for any reason, Rinia will say "bad
   layout" and exit immediately.

3. Output                                                                  m

   If Rinia finds a usuable checksum, she will say "OK." and write to
   the specified output file.  Otherwise the exit message is "fail"
   and nothing is written.

   Chances of success and how long it takes to run to completion is
   completely dominated by the layout file design.  In general, Rinia
   runs faster if the checksum is placed before the other marker
   characters rather than after, e.g.:

       a: X X XXX      b: XXXXXXXX     c: XXXXXXXX
          XXXXXXXX        X X XXX         XXXXX

   "a" usually takes the longest time, while "c" usually is the
   fastest.

   That said, each run is randomized with respect to system time, so
   it's not always certain whether Rinia will succeed in a short time
   or not.  In general, 5 marker characters is sufficient, and takes
   a few minutes.

   For reference, rinia.c was produced on a 1.7GHz machine (the
   checksum is at line 17).  Out of 25 runs, the shortest was 2
   seconds while the longest took 5 minutes.  Average was about a
   minute.  Checksum for this file (b7a81524) took about 4 minutes.

4. Algorithm                                                               3

   Inserting a checksum in the file you are computing the checksum of
   isn't quite trivial, since changing the file content would change
   the final checksum value.

   To insert the checksum, Rinia first assumes a random final
   checksum, insert that string, then modify other parts to compensate
   for the change in content.

   The compensation bytes are very easy to compute for binary files
   with enough consecutive scratch areas, but for text files with
   non-consecutive areas and limited degrees of freedom, Rinia has to
   try out all character combinations.  This is done in a hierarchical
   fashion, computing only smallest partial checksum after each
   change.

   For computers few years ago, this is probably still too slow to be
   acceptible... but at the speed the IOCCC judges run the contest
   these days, I am sure you have enough patience for it ^_^;

5. Source code                                                             =

   rinia.c should compile anywhere (but with a few warnings).  I don't
   have a big-endian machine to test but Rinia should work there as
   well.  ASCII character set required though.

   Code is formatted to the shape of "Rinia" from the anime/game
   "Moekko Company".  Of course at 90x50 it's hard to recognize anything
   ^_^;

   Rinia is the slow but hardworking android.  On some jobs she does
   very well, on others she would spend lots of time and effort but
   still fail...
