Huffman Compress: Perform Huffman compression on plaintext files

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+
+	HUFFMAN STATIC COMPRESSION
+	A PHP Implementation
+
+	by Exaton (exaton@free.fr)
+
+	Released as Freeware.
+	Use & modify as you see fit, no guarantee provided.
+
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VERSION INFO :

+	version 0.1 (22/nov/2003)
+	version 0.2 (18/dec/2003)
		Proper Huffman tree transmission


ABSTRACT :

This class is intented to perform Huffman static compression on files with a
PHP script.

Such compression is essentially useful for reducing the size of texts by about
43% ; it is at its best when working with data containing strong redundancies
at the character level -- that is, the opposite of a binary file in which the
characters would be spread over the whole ASCII alphabet.

It is questionable whether anyone would want to do such an operation with PHP,
when C implementations of much stronger and more versatile algorithms are
readily avaible as PHP functions. The main drawback of this script class is
slowness despite processing intensiveness (7 to 8 seconds to compress a 300Kb
text, about 25 seconds to expand it back).

This class will therefore probably find more of a pedagogical purpose more
than anything else. That's the context it was written in, anyway.


TERMS OF USE :

This class is provided as is, WITH NO GUARANTEE WHATSOEVER. It'll be slow, 
even if the code is optimised, very processor-intensive, probably memory-guzzling
(all output is entirely stored in memory before being written out to file),
and who knows what else Murphy might make it do to a computer.

And even if it's a canonical lossless algorithm, there even isn't any
guarantee that it'll really restore your texts properly, even though the small
battery of tests it was subjected to turned out positive.

The single redeeming quality of this class is that it is distributed as
freeware. Use it, modify it, redistribute it as you see fit, just don't say
you weren't warned that it might just not work at all, or worse. I would
appreciate your leaving my author notice in place, albeit possibly completed
by your own, but I'm not even holding you to that.


USE AND FUNCTION REFERENCE :

The 4 PHP files having been placed in the same directory, the only ones you
have to include are compress.inc.php and/or expand.inc.php according to your
needs.

-----------------
-- Compression --
-----------------

Once a CPRS_Compress object has been constructed, the following functions
are available :

+ SetFiles("path/to/source/file", "path/to/destination/file") :

This step is mandatory, as you give the paths to the file you want to
compress, and the file you want the compressed output written to. These
paths will be passed to the PHP fopen() function, see its reference for
details. Note that the paths, if local, should be relative to the location
of _your_ script, i.e. the one that has included this compression class.

+ SetDebug(string options) :

This step is optional. It enables you to ask for certain debug info to be
written to the standard output at the end of the operation. The options
string should be made up of any combination of "time", "scodes" and/or
"ratio", seperated by spaces, noting however that the selected info will
always appear in that order.
"time" will output the time taken to compress, in milliseconds.
"scodes" will output the data codes used for the characters in the
constituted alphabet.
"ratio" will show compression ratio information.

+ SetTimeLimit(int seconds) :

This step is optional. It allows you to force a certain timeout limit
for the PHP script, presumably longer than the default configuration on
your server, should the job take too long. It simply calls the PHP
set_time_limit() function.

+ Compress() :

This is the function that actually executes the job. It receives no
parameters, and is of course obligatory.

---------------
-- Expansion --
---------------

Once a CPRS_Expand object has been constructed, the following functions
are available :

+ SetFiles("path/to/source/file", "path/to/destination/file") :

This step is mandatory, as you give the paths to the file containing the
compressed data, and the file you want the expanded output written to. These
paths will be passed to the PHP fopen() function, see its reference for
details. Note that the paths, if local, should be relative to the location
of _your_ script, i.e. the one that has included this compression class.

+ SetDebug(string options) :

This step is optional. It enables you to ask for certain debug info to be
written to the standard output at the end of the operation. The only option
available is "time", to output the time the expansion operation took, in
milliseconds.

+ SetTimeLimit(int seconds) :

This step is optional. It allows you to force a certain timeout limit
for the PHP script, presumably longer than the default configuration on
your server, should the job take too long. It simply calls the PHP
set_time_limit() function.

+ Expand() :

This is the function that actually executes the job. It receives no
parameters, and is of course obligatory.


NOTE : typical use for each type of operation can be found at the
beginning of the compress.inc.php and expand.inc.php files.


EXTRA NOTICE :

This class has been tested essentially functional on PHP 4.3.3 . No
certainty is to be had for any version of PHP lower than that.

Please also note that some technical considerations apart from the core
Huffman static algorithm have probably not been implemented after
any standard in this class. That means that any other compressed file,
even if you have reason to be certain that it was produced using the
Huffman static algorithm, would in all probability not be usable as
source file for data expansion with this class.
In short, this class can very probably only restore what it itself
compressed.

Anyway, thanks for using ! No feedback would be ignored. Feel free
to tell me how you came in contact with this class, why you're using
it (if at liberty to do so), and to suggest any enhancements, or of
course to point out any serious bugs.