Amiga Elysian Archive/AmigaElysianArchive.iso/compress/pcompres.lha/PCompress/P-Compress.doc

Text File | 1991-11-21 | 14KB | 283 lines

PRE1

                           P - C O M P R E S S V1.2
    INTRODUCTION

     P-Compress is a compression/de-compression tool designed to meet the great
  majority of the requirements of users efficiently and economically while
  being very easy to use.  It will compress single files, drawers or complete
  disks, preserving disk and drawer structures.  Individual files can be joined
  into a single PACK, similar to an archive and by using PACKs two uncompressed
  disks will normally fit on one.  Drawers and disks can be copied from one
  place to another, selected files or classes of files being compressed and the
  remainder just copied.  P-Compressed files, including sounds, pictures and
  animations, can be displayed by P-Reader without prior decompression, and P-
  Compressed texts can be loaded into and saved from P-Writer.  The latest
  version of P-Reader is being used to display this file.

    Two important areas not covered at present are:
      Hard-disk back-up. Use a specialised programme (eg BRU).
      Self-extracting executables.  Use Imploder from Fish 422.

    One of the main uses of P-Compress may be to reduce the size of your own
  personal library collection of utilities, data, games, code examples, stored
  away for occasional reference.  By just compressing all data, leaving icons
  and executables untouched, and using P-Reader as the basic text reader and
  display tool, my own "library" of 35 disks reduced to 25.  Caution is needed
  when doing this as data files used by the executables must be left
  uncompressed.  P-Compress is designed to make the selection process as easy
  as possible.

     P-Compress employs the latest LZH compression technique using code by
  Barthel and Krekel, modified to limit memory requirements.

     This release also includes the small utility P-Unpack, whose sole purpose
  in life is to unpack Packs.  Details are on Page 8.


   COMPARISON WITH ALTERNATIVE PROGRAMMES

    Whole disk compression tools:  eg LHWARP, Zoom.

     When used to PACK a complete disk P-Compress only compresses the files on
  the disk and not such additional data as boot-blocks.  As a result output
  will be smaller than that of true whole-disk tools. P-Unpack can write a
  standard boot-block to the re-constituted disk.  Speed is comparable but
  memory usage much lower.   If you really need to include everything on the
  disk, Zoom is recommended.

    Archivers:  eg  LHArc, PKAZip.

    To suit their role in the maintenance of archives these include a host of
  facilities which are of little or no use to most of us.  As a result they are
  not easy to use. One effect of the complexity is that with some combinations
  of commands and switches files can be lost. (Tip: always use the extended
  filenames switch)  As far as performance goes P-Compress sacrifices about
  0.5% in efficiency for the sake of decompression speed and low memory
  requirement for large files.  It is faster and uses less memory than LHArcA
  and much faster than LHArc.  PKAZip is very fast, efficiency sometimes better
  sometimes worse, memory useage greatly excessive.  Large archived collections
  of files cannot be handled by single-drive Amigas without expansion memory
  (unless a vast number of disk-swops are acceptable),  PACKS can.

     General compression tools: eg Power Packer

    An excellent programme in its day the current PD version of PowerPacker is
  completely outclassed by the new wave of LZH compression tools - although
  decompression is fast.  As far as ease of use is concerned users should form
  their own judgement.  PowerPacker has the ability to create self- extracting
  executables which P-Compress does not do at present, however Imploder handles
  this particular job better and more quickly.

   Some comparative performance figures are given at the end of these
  instructions.

   INSTRUCTIONS

   P-Compress opens a window on Workbench showing:

    On the left   Progress window.
    Top right     Decompress window.
    Centre right  Compress window.
    Bottom right  Execute window.

   If you have the Arp library installed the programme will use the Arp File-
  Requester, otherwise a simple string gadget requester will appear.  If you
  are using the latter to call a drawer the entry must end with a slash /.

  P-Compress can be started from the cli or by double-clicking its icon.

    DECOMPRESSION

  Click From.    File requester will come up over the progress window.
  Enter or select the drawer, or
  file to be de-compressed.  Click OK
  (or cancel).  Selected reference
  will be shown in the From box.

    Click To.   File requester will
  re-appear.  Enter/select a disk, file
  or drawer as required. If an existing
  file other than a PACK is selected
  but a drawer or disk was entered at From, a warning will appear.  Otherwise
  new files will be opened as necessary. A PACK can only be decompressed to a
  disk or drawer -  a file entered at To will be ignored and the programme
  will look at its path to decide where to place the unpacked output.
  Compressed files will be decompressed to the indicated location, uncompressed
  files will be just copied.  Name and size of the file being handled appears
  in the progress window.  On completion a summary will appear at the bottom of
  the Decompress window (except where only a single file has been called).
    #! 1 42 2 0 decompress.brush
    The programme will recognise whether the input is a normal file or a PACK,
  and will act accordingly.  PACK in the execute window should not be switched
  on.

    If you run out of disk space before decompression is complete you will be
  asked to insert a new disk.  On completion delete any empty drawers on the
  disks and transfer icons where necessary.

    Before decompressing compressed files a checksum (CRC) is read and checked
  - if an error is found an appropriate warning will be given and the
  offending file passed over.
  #! 1 42 15 0 compress.brush
    Before an existing file is overwritten you will be asked to OK it.
  Clicking OVERWRITE in the execute window suspends this feature, which is
  also  suspended when a PACKed file is being decompressed.  Click GO in the
  execute window to start decompression, CANCEL to cancel the process, and QUIT
  to close down.


    COMPRESSION

   Select From and To in turn as
  before and enter or select the source
  and destination references.  Either a
  disk, drawer or individual file may be
  selected. If a disk or drawer is to be
  compressed click on one or more of the
  boxes below to indicate the types of
  file to be compressed, the remainder
  will just be copied.  Copied files are
  not provided with Checksums.

     DATA  "Project" type data files such as texts, IFF pics, animations etc.
     ICONS You may want to leave icons uncompressed.
     EXEC  Libraries and all executables.

    If you need to select specific individual files to be compressed or just
  copied use ASK - the programme will halt at each file and ask for
  instructions.

    Normally when compressing a file or drawer each file is transferred to an
  equivalent place at the output location, new drawers being opened as needed,
  so that the original structure of drawers and their contents is preserved.
  Alternately a PACK can be created in which all the files are joined into one
  compendium file or PACK.  An individual checksum is provided for each of the
  files contained.  The name PACK will be appended to any filename that may be
  inserted at To.  On decompression the original structure is re-created.

   If you run out of disk space before compression is complete you will be
  asked to insert a new disk (except where a PACK is being made - a file
  cannot be split between two disks).

    Click OVERWRITE, PACK as necessary, and then GO to start compression.
  #! 1 42 7 0 exec.brush
    Progress and final summary will be shown as before.


    EXECUTION

   Click OVERWRITE if existing files are to be overwritten.
   CLICK PACK if you wish to put all the individual files into a single PACK.
   Click GO to start compression or decompression, CANCEL to cancel the
  process and QUIT to close down.



     COMPARISONS

     Three files have been used:
       File 1 is a HAM picture.  Length 92872 bytes.
       File 2 is an executable file.  Length 28792 bytes.
       File 3 was made up by joining a general mixture of texts, executables
         and icons into a single large file.  Length 608440 bytes.

                               Size            Compress        Decompress
  File 1
    LHArcA                    51812            1min.08secs     33secs
    PowerPacker (fastest)     64412            2min.37secs     17secs
    PowerPacker (best)        54196            23mins.45secs   16secs
    PKAZip                    53407            45secs          21secs
    P-Compress                52136            49secs          21secs

  File 2
    LHArcA                    15788            26secs          11secs
    PowerPacker (good)        17122            2min.11         9secs
    PKAZip                    15919            24secs          7secs
    P-Compress                15816            17secs          8secs

  File 3
    LHArcA and PKAZip failed - out of memory.
    PowerPacker not tried - out of patience.
    P-Compress                287372           6m.28           1m.48

  In all cases compression/decompression was from disk to RAM: using an Amiga
  500 with 1M of memory.



                         P - U N P A C K V1.2

    When sending out a disk containing a PACK you will normally include on the
  disk the means of decoding it.  This can of course be P-Compress itself, but
  the considerably smaller P-Unpack may be used instead.  The end result is
  the same but P-Unpack provides two further advantages:

     It provides the efficient disk-swopping facilities needed by single-disk
    -drive Amigas with memory that is not sufficient for the whole pack to be
    copied to and decompressed from ram.

     By writing the icon with the ToolType "boot" the decompressed output disk
    is made bootable.  (Not functional for the single-floppy-drive user).

    P-Unpack is called as the Default Tool of a Project icon for a PACK file.
  When the icon is clicked the PACK will be decompressed and the original
  structure of files and drawers copied to a disk.

  Preparation - Sender

    The Pack should be created in the normal way with P-Compress.  Prepare
  a PROJECT Icon for the Pack, and write P-Unpack as the Default Tool. Include
  a path (e.g :c/P-Unpack) if necessary.  If the output disk is to be made
  bootable write the single word boot into the Tool Types space.  Include
  P-Unpack on the disk along with the Pack or Packs.  It is a good idea to
  name the pack "CLICK-ME" or incorporate "click-me" into the icon so that the
  recipient knows what to do. The recipient should not need any other
  instructions.

  Use - Recipient

   The recipient will boot the received disk normally and faced with an icon
  that incorporates the instruction Click-me will double-click it.  P-Unpack
  will check the number of floppy drives connected.

    If there is more than one floppy drive connected a requester will appear
  asking the user to select one, insert an empty disk, and click go.  Once
  decompression is under way an Abort gadget is added.  Clicking on this will
  stop the programme on completion of the current file.  If the pack includes
  a disk icon, this will be adopted and seen if the disk is removed and
  re-inserted.  If the Tool Type boot was written into the icon the output disk
  will be bootable.  If the expanded PACK is larger than a single disk, a
  notice will call for a new disk when the first is full.

    Where P-Unpack finds only one floppy drive a different requester will
  appear asking the user to insert the source disk and click go.  Decompression
  to RAM will continue for as long as memory is available and the user will
  then be asked to insert the output disk - ram will be copied to this.  Disk
  swopping will continue until decompression is complete - four or five swops
  may be needed.  No early warning will be given of a full disk, but a new
  disk can be inserted at any of the disk-swops. The output disk can not be
  made bootable, otherwise the  final result is the same.


           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    P-Compress and P-Unpack are Freeware.  They may be copied and distributed
  freely and used without charge for non_commercial purposes.  Authority for
  commercial use should be obtained from the author below.

    No responsibility can be accepted for any loss occasioned by use of these
  programmes.

    Comments, suggestions, bug-reports all welcome.
   Chas A. Wyndham,
   1265 Canning Mills Road,
   Roleystone,
   WA 6111.
   Australia