                  unice68 - ice packer and depacker
                                   
                 unice68 is part of the sc68 project
                       
                    (C) 1998-2015 Benjamin Gerard


ABOUT UNICE68

  unice68 project  is a  "C" library  and a  command line  program for
  packing and depacking !Ice compressed files.

  Both the packer and depacker are buffer based only, you can't stream
  them.

  The depacker is based on the  original ICE unpack public source file
  version 2.40.  The  packer is based on the  original PACKICE version
  2.35.  This difference does not  really matter as the file generated
  by the 2.35  cruncher are compatible with the  2.40 decruncher.  The
  only problem is the magic 4CC identifier being different ('Ice!' for
  the version 2.35 / 'ICE!'   for the version 2.40).  Unice68 depacker
  will accept both.  Unice68 packer  will generate the 2.40 by default
  for  compatibility  issue, even  if  it  should  not.  It  is  still
  possible to force the header with the library and the cli program.

  In the begin  unice68 was a front-end to the  original *native* ICE!
  depacker  routine written  in  68000 assembler.   It was  functional
  enough  but pretty  much  slow so  I decided  to  convert the  68000
  assembly to "C"  code. This conversion is straight  forward and kind
  of ugly.

  In 2013 the packer source which was not available until then came to
  my  attention  (I  think  it  was  released  in  2011  but  I'm  not
  sure). Because sndh files is the  dominant format sc68 need the best
  possible support for  them. Also it save me the  time to maintaining
  the sc68 music database. A few sndh files are bugged and too many of
  them  lack  the  duration  information  in  their  header,  this  is
  something I  really don't like with  them so I intended  to fix that
  and   submit   the   modified   file  back   to   their   respective
  maintainer. SNDH files being by convention  ICE! packed I can now do
  that  without launching  a ST  (simulator or  real) to  achieve this
  goal.

  Just like the depacker I have first tried a simulated version but it
  was clearly too slow  so I decided to do the same  I had done before
  with the  depacker: to  convert the m68k  assembler source  into "C"
  code straight  forward. Maybe  someday I  will take  the time  to do
  something cleaner but do not expect too much.

  To perform  the first simulated try  with the ice packer  the source
  had to  be cleaned.  Mainly  stripping every thing  unnecessary like
  TOS/GEM/AES calls to keep only the  main crunch routine. Also in the
  process it has become PIC (position independent code) and re-entrant
  (variables are stored in the stack rather than globally).


ABOUT ICE!

  ICE was a  common compressor running on Atari  ST(tm) and compatible
  machines made by  Axe of Superior. sc68 project needs  to handle the
  many ICE! compressed Atari ST music files (namely sndh files).

  From the source files you can read:

    PACK-ICE is simply  the best packer that's available on  the ST. I
    used especially  much time to  get the depacking-routine  as small
    and fast (!!!) as possible
