Re: Compressing ProDOS File Type Table

[Mike Pfaiffer <mike@digitalcivilization.ca>]

Jonathyn Bet'nct wrote:
> I'm writing a program launcher in assembly language, and I want to
> have a table of all 136 defined ProDOS file types (found at
> http://www.geocities.com/jonrelay/software/a2info/abftypes.htm) as
> part of it.
>
> To keep the program small and simple, I want to compress the table
> like BASIC.SYSTEM compresses its keywords (or at least how I _think_
> it does). For example, I can take the types AWP, WPF, PFS, FST, STN,
> TNJ, JAP, PTX, TXT, and TOL (totaling 30 bytes) and compress it into
> AWPFSTNJAPTXTOL (which is only 15 bytes).
>
> Doing this by hand, the shortest string I came up with was 277 bytes
> long. I want one that's 256 bytes or less (so I can fit it in a
> single page of memory).
>
> Here's my question: Is there a program out there that can compress
> strings this way into the shortest string possible so I don't have
> to?
>
	There is something else you can do. If you won't care about speed you 
could take the letters (normally 8 bits), disgard the MSB and compress 8 
bytes into 7.

	You could also come up with a code describing the 26 letters A - Z and 
the numbers 0 - 9 and perform a similar compression. Looking at an ASCII 
table it could handle from 0 - 63 characters (with some left over) very 
nicely. This should compress down to about 25% of the size. You may want 
to consider taking the number of possible characters down to 0 - 47 and 
get a tighter compression but at 0 - 63 you get four characters per byte 
which should make uncompression easier.

				Later
				Mike



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