Hello everyone, I have been trying to figure out the best way to work with arrays in assembly, and I have been running into some problems. I would like to add a column to this 2D array, but I am not sure of the best way to do it. Would I have to copy the original data to a separate area of memory, or is there an easier way, simply by counting the original amount of columns per row, and then adding a 0 onto the end of every line?


Code:


To something like this:


Code:


Any help is much appreciated!
(yes, this is really not how the bytes will appear in memory, it is just easier for me to think this way.)

Assuming that in the original data space you have enough extra free memory to store the extra data, you could do the following:

Start at the last row of the 12x8 array. Move the last row of 12 bytes forward 8-1 (7) bytes.
Go to the start of the second last row, and move this forward 8-2 (6) bytes.
Go to the start of the third last row, move this forward 8-3 (5) bytes.
Continue until you've moved the second from the top row forward 8-7 (1) byte.

These above loops could be accomplished using a B register counter, and then working with HL, DE, BC & the ldir instruction. In each loop, the DE destination would have to be calculated to be n bytes ahead of HL (the source), depending on the value of the B register counter (don't forget to push bc / pop bc at the start/end of your loop, as you'll be using BC for the ldir instruction).

You will then have 1 byte space between each row. These values won't necessarily be zero, so if you want this you will need to go through and zero these, or you could incorporate this into the above loop.

Sorry, that's probably a really bad explanation and just off the top of my head, but hopefully it's a starting point

Actually, if you're moving data forward, you'll need to do a reverse copy with LDDR to make sure you don't overwrite part of the row before copying it. But that actually makes things a lot easier anyway, because then it goes like:


Code:

Yes, my bad. What calc84maniac said

Great, thank you guys so much! I had tried before hand to do this with LDIR... It didn't come out to great. I imagine that I could simply restructure this to take out a column using LDIR. Once again, thank you!