Light ROM 1/LIGHT-ROM 1 (Amiga Library Services)(1994).iso/ffdisks/d884.lha/P-Compress/P-Compress.doc

Text File | 1993-07-16 | 16KB | 324 lines

PRE1

                           P - C O M P R E S S V2.9
    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 unchanged.
  Alternatively if the P-Suite utility P-Fixlib is to be used (which allows DOS
  to treat compressed files as though they were uncompressed) the whole disk
  can be compressed, doubling its capacity.

     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 from line 229 on.

   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).  The P-Compress PACK option can be regarded as a very
  simple archiver and is faster and uses less memory than LHArcA  and much
  faster than LHArc.  PKAZip is very fast, efficiency usually poorer, memory
  useage greatly excessive.  The new Shrink sets a new standard in efficiency,
  and although it uses a lot of memory and is a bit slow it competes with LHA
  for the title of the best current archiver.  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.

   This version checks any file presented for compression or decompression to
  see if it has been compressed with PowerPacker.  If so it is automatically
  decompressed.  Self-executing executables are excluded.

   Some comparative performance figures are given at the end of this doc.

   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.

   Color selection gadget can be found at the top of the lower right P-Compress
  logo.  Click it to cycle the available color palettes.

   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.
   #! 1 42 6 0 decompress.brush
    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).

    The programme will recognise whether the input is a normal file or a PACK,
  and will act accordingly. PACK in the execute window need not be switched on.

    You can decompress back over the original - with the same reference entered
  at From and To.  Sufficient space must be available on the disk to take the
  file currently being decompressed as well as the original (later deleted).

    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.  Note that when checking for space
  no account is taken of whether an existing file is being overwritten.  This
  can mean that the request is made when not strictly needed.  Collect the
  extra file or files on another disk and copy back.

    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.

    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.
    #! 1 42 3 0 compress.brush
   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 listed 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.
     HEXEC Executables are stripped of any debug or symbol hunks. In normal
                       operation these are not needed.

    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.

    If HEXEC is selected the stripped file will be put into a temporary file
  RAM:S.  If EXEC is also selected RAM:S will then be compressed to the final
  destination, otherwise it will be just copied; the sizes of the original
  file, RAM:S, and the final output will be shown.

    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.
  HEXEC is not functional when compressing to a pack.  Note that the PACK that
  is to be created must be in a different drawer from that being packed (or a
  different disk if a whole disk is being packed), otherwise P-Compress will
  try to include the PACK within itself - and fail.

   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).  (But see the comment in the decompress
  section.)

    Click OVERWRITE, PACK as necessary, and then GO to start compression.

    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.
    #! 1 42 5 0 exec.brush
    Note that you may enter the same reference in From and To, allowing the
  direct replacement of a file by its compressed (or decompressed) image. An
  intermediate temporary file in RAM is used, which of course means that memory
  consumption is increased.  The original is not overwritten unless the
  compression or decompression operation returns correctly, however for safety
  's sake it is always better to have a backup.


   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.


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

    A large Byte of thanks to Steve Bolton of South Australia whose comments
  and suggestions have greatly improved this programme.

    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