Hello all,

In C you might use initialize an array such as:



In assembly you would basically 'set aside' a chunk of memory and use the syntax of your compiler to tell it what values should fill that chunk like:



How is this accomplished in Forth? I can use:



so set aside some memory for an 'array' but what is the Forthy way to initialize the values therein?

Thanks!

DOH! I swear I searched for an answer before posting. I glanced through ''Starting Forth' again and found the section cryptically labeled 'Initializing an array'

There is one detail about that to remember (bit me at one point): The comma saves a whole cell, but if you want to save a byte (say, characters), you need "c-comma". For the most 6502 machines, a cell is two bytes, though I think on my Ubuntu computer with Gforth it's 8 bytes (64 bit CPU), so this can save serious space.

Thanks! I had not realized there was a c, but it makes sense as it is analogous to c@ and c!. For what I was thinking about I did need a double so I had not considered there might be a byte version of the same command.

I was doing a simple plot to the screen memory and when you use the standard x+n*y to calculate the memory address you pay a dear price for the multiplication on a small system like the C64. In the past if I was only moving one line in Y I would just add the appropriate offset for a line (40 in this case) which is much faster. I dawned on my that if one could spare 50 bytes (two bytes for 25 screen lines) to save the offset of the start of each line in an array [0, 40, 80, 120...] then the Y position could be used to index into the array to retrieve the correct offset (using a lshft since we have to index two bytes at a time. So typing form the top of my head:



I'm not sure if this would actually be any faster but I guess there is nothing to do but try it and see.

Charlie H. has been doing some awesome work in PETTIL. You should check it out, because a lot of his meticulous optimizations can be easily ported to the C=64.

https://github.com/chitselb/pettil

https://pettil.tumblr.com/

(it looks like his tiddlywiki is no longer working, but maybe that's just a temporary or treatable condition ... it happens to the best of us as we get older ...).

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Got a kilobyte lying fallow in your 65xx's memory map? Sprinkle some VTL02C on it and see how it grows on you!

Mike B. (about me) (learning how to github)

Forth on the PET. That would be pretty cool. Might give me a good excuse to dig out my PET and see if I can fix whatever it was that popped and stunk up my house last time I used it. lol

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Cat; the other white meat.

Thanks, I'll give that a read tonight. I have been using: https://github.com/jkotlinski/durexforth for the C64