Re: Data compression

 BBS: Inland Empire Archive
Date: 10-04-92 (09:01)             Number: 347
From: GLENN KINEN                  Refer#: NONE
  To: BOB EDWARDS                   Recvd: NO  
Subj: Re: Data compression           Conf: (2) Quik_Bas

> ->        This was all off  the  top  of  my  head,   but  you  should
> ->hopefully get the general idea of it.

> Rich, where does RLE fit in?

 I know I'm not Rich (Yep, I'm quite poor <g>), but here is a brief demo
of RLE-Run Length Encoding.

 Pick a character from the ascii set which is not in the file. (I'll
 pick '*')

      Now say you wanted to compress:

    aaaaBBBBBBBBccOOOOOOO;;;;;;opp

You find all letters which are repeated more than 3 times in a row (more
on this later). Next, you put '*' into the compressed file, as the
initializer, or for decompressor info. (The decompressor uses this so it
would know the next 2 bytes tell it what to do). Then you add the
character which is repeated more than 3 times (not 3 more than 3),
*a; then you add total number of times repeated; *a4. See you compressed
4 bytes in 3 bytes, you can't use this on 3 or more bytes becaus eyou
will get no compression, or actully make the file LARGER.

So the compressed version of the string I put above would be:

*a4*B8cc*O7*;6opp

31 was the original size - 17 the compressed. Any questions? ;-D

 -Glenn

 * SLMR 2.1a * Computers All Wait at the Same Speed.

--- Maximus 2.01wb
 * Origin: Miami Amateur Computer Club BBS  HST/V32b/V42b (1:135/110)