Re: Data compression (in Ada)

[tojst1+@pitt.edu (Tore Joergensen)]

Mike Roske (mroske@mailgw.sanders.lockheed.com) wrote:
: I am looking for an Ada 83 implementation of a file
: compression/decompression algorithm (a la Zip).  It doesn't have to be
: compatible with Zip.

: I have a need to take a file, compress it, and store it on an embedded
: file system (part of the load process).  At run-time I will be
: uncompressing the file into RAM in order to access the data.  There 
: isn't enough EEPROM to store the uncompressed file, but I have enough
: RAM once I get started.

Try to find some information on LZW compression. This is the compression
algorithm Zip is based on, and it's fairly easy to implement. I'd 
recommend to use a table index-size of two bytes and a data-size of
one byte (then you will avoid having to shift the bits), unless this
doesn't make sense for your program. I made a LZW compression program
in Ada as an assignment in a course, but I don't have the code anymore.
It is really easy to implement, and the nice thing about it is that
it builds the compression-table while you write and read the file, so
you don't have to store the table with the file.
-- 
+-------------------------+-------------------------------------------+
| Tore B. Joergensen      | e-mail : tore@lis.pitt.edu                |
| Centre Court Villa      | web    : http://www.pitt.edu/~tojst1      |
| 5535 Centre Avenue # 6  |                                           |
| Pgh, PA 15232, USA      | Norwegian MSIS-student at Univ. of Pgh.   |
+-------------------------+-------------------------------------------+