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Lhwarp
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1990-02-14
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LHWARP 1.21
6th January, 1990
A disk tracker for the Amiga
Written by Jonathan Forbes
What is Lhwarp?
(Pronounced L-H-WARP)
Lhwarp is a program which will read tracks directly from your floppy disk,
compress them, and output them to a file. The advantages of using Lhwarp are:
o The entire disk structure, including the boot block, is preserved.
o Lhwarp will always produce a smaller output file than ARC, ZOO or WARP.
(note: this is only true when the default compression algorithm is used)
o Lhwarp will only archive sectors which contain data, by using the disk's
bitmap (however, Lhwarp will gladly compress every single sector on
the disk, if you wish.)
o Using Lhwarp is much less hassle than archiving each and every file
individually.
o The bootblock of any disk being either read or written is displayed, so
that bootblock viruses can easily be found.
Lhwarp will produce files much smaller than those produced by Warp, due to
the fact that Lhwarp uses a more efficient compression algorithm (Adaptive
Huffman Encoding); the same algorithm used in LHARC. Typically, an Lhwarp
file will be 80% of the size of an equivalent Warp file, resulting in quite
reasonable hard drive space savings.
In addition, Lhwarp will only archive sectors which contain data; deleted
information is not archived (unless you explicity request this to be done.)
When compressing or decompressing data, sectors which contain data are marked
with a '.' character, while sectors which do not contain data are marked with
a '_' character. If the -m option is specified, all sectors will be marked
with '.' automatically.
Lhwarp's main (and perhaps only) disadvantage is that compression time is
very large; it can take from 20 to 25 minutes to compress an entire disk
(80 tracks.) There is not too much which can be done about this; you have to
pay a price for the extra power.
However, this is not as bad as it may seem; a disk only has to be Lhwarp'd
once; after Lhwarp'ing, the output file will be transferred via a modem, from
BBS to BBS. Because the file will be that much smaller than an equivalent
file produced by Warp, the file will take less time to transfer, resulting in a
lower phone bill. And, as mentioned before, it will occopy less space on the
destination system.
Algorithms
For those who simply must have a faster compression rate, Lhwarp provides
two additional compression algorithms; squeezing and vaporising (the latter is
the 14 bit version of UNIX Compress.) Both are much faster than the LHARC
Adaptive Huffman Encoding algorithm (called "freezing.") However, neither of
them comes close to the compression ratio of freezing.
Even so, the huge speed increase and reasonable compression rates should
appeal to those who are less concerned with compression efficiency, and more
concerned with speed.
Freezing remains the default compression mode. Using the -c switch will
cause the disk to be vaporised (not literally), while the -s switch will cause
the disk to be squeezed. The -b option will cause each individual track to be
either vaporised or squeezed, depending on which produces the smallest output.
The -q option will cause Lhwarp to use its fastest and most reasonable
algorithm on the disk. Currently, this is squeezing. Admittedly, vaporising
is faster, but vaporising often generates track output which is actually
larger than the track itself, and squeezing is almost as fast (certainly it's
faster than freezing.)
The most recommended option for speed, is the -b option, to select both
algorithms; compression time is only a few minutes longer than that of one of
the algorithms, and different algorithms sometimes work better for different
disks.
You cannot currently combine freezing with any other algorithm; this is for
your own benefit; I have yet to see freezing beaten by vaporising or squeezing
for any one track, ever! However, if you find that vaporising and squeezing
frequently do compress tracks more efficiently, please inform me.
To compress the NewTek DYNAMIC HI-RES demo disk:
Compression Size Time (approximate)
----------- -------- ------------------
Freezing 671630 20:00 minutes
Vaporising/Squeezing 770722 10:30 minutes
Squeezing 803714 07:30 minutes
Vaporising 869515 06:30 minutes
Warp program 796665 15:00 minutes
At this point in time, Lhwarp does not check to see if the output for a
track is larger than the input; this is why vaporising produced such a huge
file; many tracks compressed from 11k to 13k. This will be corrected in a
future version.
Viewing
Lhwarp also supports viewing; you may see how Lhwarp has compressed a disk
(which tracks are contained in the file, which algorithm was used to compress
them, the source and destination lengths of each track, the number of sectors
compressed, and the sector map of each track.) The viewing option will also
display any attached text.
After any attached text is displayed, you must press return; this was
implemented so that the displaying of the boot block won't scroll the text off
the screen.
More Information
Lhwarp output files have the suffix ".LHW". If the filename you give
Lhwarp does not end in ".LHW", Lhwarp will append ".LHW" to it. Please leave
the suffix alone, and don't change it to ".WRP".
The Adaptive Huffman Encoding algorithm was originally coded by Haruyasu
Yoshizaki, and is the same algorithm used in LHARC 1.13c. When the more
efficient LHARC 2.0 arrives from Japan, that algorithm will instead be used.
Lhwarp was compiled and very heavily optimised under Lattice C 5.04. Even
though Lattice produces very fast code, Lhwarp needs all the speed it can get.
I have rewritten a few of Lhwarp's compression functions in assembly language,
and performance has improved significantly.
Nevertheless, the Lzhuf routines, which are now a mixture of Lattice C 5.04
code and assembly language, are much faster than those in either Amiga Lharc,
or the previous versions of Lhwarp. When compressing an arbitrary 40k file:
Encode time(s) Decode time(s)
Lharc 60 15
Lhwarp 1.03 55 13
Lhwarp 1.10 47 11
Lhwarp 1.11 39 11
Lhwarp 1.20 39 10
Lhwarp 1.21 39 10
Parameters
To view Lhwarp's parameters, type "Lhwarp"; they are included within the
program. You will be presented with:
Usage: LHWARP <Command> [-option] <Unit> <Filename> <Start> <End> <TextFile>
<Command> Read or Write
-m: ignore bitmap
-q: quick compression
-s: squeeze
-c: compress-14 (vaporise)
-b: both squeeze/vaporise
-v: view output file
<Unit> Drive number (0 for internal, 1 ... 3 for external)
<Filename> Output|Input filename
<StartTrack> Track number (0 ... 79) [valid only in read mode]
<EndTrack> Track number (0 ... 79) [valid only in read mode]
<TextTFile> Append text in <TextFile> to output file [optional]
Examples are:
a) Lhwarp READ 0 mydisk 0 79
This will read tracks 0 to 79 of the disk in drive 0 (i.e. the entire
disk), and will output the result to "mydisk.lhw" Only sectors which contain
data will be archived.
b) Lhwarp READ 0 mydisk 0 79 mytext
This will read tracks 0 to 79 of the disk in drive 0 (i.e. the entire
disk), and will output the result to "mydisk.lhw". Only sectors which contain
data will be archived. The text from the file "mytext" will be imported to
the output file. Any text stored in the output file will be displayed when
the disk is unarchived.
c) Lhwarp -m READ 0 mydisk 0 79
This will read tracks 0 to 79 of the disk in drive 0 (i.e. the entire
disk), and will output the result to "mydisk.lhw". All sectors will be
archived, regardless of whether or not they contain data; the disk's bitmap
is ignored with the '-m' option.
d) Lhwarp WRITE 1 mydisk
This will output all tracks stored in mydisk.lhw to drive 1. If any
text was in the output file, it will be displayed.
e) Lhwarp -c READ 0 mydisk 0 79
Same as a), except that the disk will be "vaporised."
f) Lhwarp -s READ 0 mydisk 0 79
Same as a), except that the disk will be "squeezed."
g) Lhwarp -b READ 0 mydisk 0 79
Same as a), except that tracks will be either squeezed or vaporisied,
depending on which is more efficient.
h) Lhwarp -m -c READ 0 mydisk 0 79
Same as e), except that the bitmap will be ignored.
i) Lhwarp -v mydisk
View composition of the file MYDISK.LHW.
Please note that you must combine options in the format of:
'Lhwarp -a -b -c ...'
Not:
'Lhwarp -abc ...'
The latter may have unpredictable results (most probably all options but
'-a' will be ignored.)
Virus detection
Some people have complained about Warp in that it aids the spreading of
boot block viruses. It is for this reason that Lhwarp will display the
bootblock of any disk it reads or writes, so that one can see what is being
Lhwarp'd. Any non-standard looking bootblock should be viewed with suspicion.
If you see a non-standard bootblock in read mode, this means that the disk
you are reading from might possibly contain a virus. If you see this in write
mode, it means that the file you are writing out to your disk may contain a
virus. In either case, you should load a virus checker to make sure (such as
VirusX 4.0)
Specifications
Lhwarp uses ETD_READ and ETD_FORMAT to read/write directly from/to the
trackdisk.device. The 16 bytes of label information for each sector are saved
in the output file. A 32-bit CRC protects data integrity.
Future Possibilities
o Support for raw track reads and writes
o Merging output files
o Mix raw/normal tracks in a single file
Acknowledgements
Huffman routines - Haruyasu Yoshizaki (lzhuf.c, v1.13c)
Compress - S.Thomas, J.McKie, S.Davies, K.Turkowski, J.Woods,
and J.Orost (compress.c)
Squeezing - William Swan (sq.c/usq.c)
Bitmap information - Leo Schwab (diskmap2.c)
This Program
Lhwarp is a freely distributable, copyrighted piece of software. You do
not have to pay money to use it, and may upload it wherever you choose, but
you are not allowed to sell Lhwarp for profit, or include Lhwarp on a disk
which is sold for profit, without the author's (Jonathan Forbes) permission.
I can be contacted at 416-927-7844 (voice.)
Disclaimer
I am in no way responsible for anything this program does; you are using
it entirely at your own risk, so if you are kidnapped and held hostage by
Libyan terrorists, don't blame me!
Important note
The STACK SIZE requirements have increased again, slightly -15k or so
should be adequate. This will be corrected in a future version.
Conclusion
So there you have it; Lhwarp is faster and more efficent than Warp, and
Lhwarp is being updated; Warp isn't! All that's missing is the support for
raw track reads/writes, which will be implemented as soon as I find out how.