PPMD(1)PPMD(1)NAMEppmd - file-to-file compressor
SYNTAXppmd <e|d> [switches] <FileName[s] | Wildcard[s]>
DESCRIPTION
PPMD is written for embedding in user programs mainly and it is not
intended for immediate use. The author was interested in speed and per‐
formance improvements of abstract PPM model [1-6] only, without tuning
it to particular data types, therefore compressor works good enough for
texts, but it is not so good for nonhomogeneous files (executables) and
for noisy analog data (sounds, pictures etc.). Program is very memory
consuming, you can choose balance between execution speed and memory
economy, on one hand, and compression performance, on another hand,
with the help of model order selection option (-o).
OPTIONS-d <delete file[s] after processing, default: disabled>
-s <silent>
-fName <set output file name to Name>
-mN <use N MB memory - [1,256], default: 10> The PPMII algorithm
might need a lot of memory, especially when used on large files
and/or used with large model order. If ppmd needs more memory
than you give it, the compression will be worse. The exact
effect is dependent on the -r option.
-oN <set model order to N - [2,16], default: 4> Bigger model
orders almost surely results in better compression and surely
more memory and CPU usage.
-r{0,1,2} <>
Methods of restoration of model correctness at memory insuffi‐
ciency:
'-r0 - restart model from scratch'. This method is not opti‐
mal for any type of data sources, but it works fast and effi‐
cient in average, so it is the recommended method (default).
'-r1 - cut off model'. This method is optimal for quasista‐
tionary sources when the period of stationarity is much larger
than period between cutoffs. As a rule, it gives better
results, but it is slower than other methods and it is unstable
against fragmentation of memory heap at high model orders and
low memory.
'-r2 - freeze model'. This method is optimal for stationary
sources (show me such source when You will find it ;-)). It is
fast and efficient for such sources.
EXAMPLES
To run this program the standard way type:
ppmd e /tmp/myfile
Alternatively you can run it as:
ppmd-e -o 16 /tmp/myfile
AUTHORS
PPMd was written by Dmitry Shkarin <dmitry.shkarin@mtu-net.ru> and
Dmitry Subbotin.
SEE ALSOgzip(1), bzip2(1).
PPMD(1)
