Subject: GROB Compression Programs (HP48SX)
Organization: Chalmers University of Technology, Gothenburg, Sweden
Lines: 64


GROB COMPRESSION / UNCOMPRESSION PROGRAMS
=========================================

Here is two small programs that compresses and uncompresses GROBs. The
compression method is simple Run-Length Encoding, which means that a number 
of equal nibbles will be compressed into three nibbles saying "here comes
57 nibbles of zeroes" for example.

The efficiency of the programs depend largely on the type of GROB that you
are using. A picture with large areas of a single pattern and horizontal
lines will perhaps be compressed to 1/20 of the original size, but a very
complex picture may not be compressed at all (or even increase in size).

Since UPGROB is very small (145 bytes) and fast, it can easily be imple-
mented in games and other programs, where you wish to have nice screens
without running out of memory. It will probably save memory even if you
only have one screen GROB.

The programs behave nicely with all necessary error checking.


PGROB (compress GROB)
-----
1: GROB  -->  1: Binary Integer


UPGROB (uncompress GROB)
------
1: Binary Integer  -->  1: GROB


(Note: the binary integer that PGROB returns is never 16 nibbles long.
This means that you cannot edit it, and therefore you cannot crash
UPGROB this way.)


PGROB in ASC-format


Happy graphing!

Erik Bryntse
erikmb@cd.chalmers.se