[keithnz]

I find it funny that people enjoy the nostalgia of things like 6502... I loved my Atari 800XL, but wistfully dreamed that computers might one day be able to handle 320x240 with 256 colours.... boy... that would be good! Meanwhile I was hand assembling 6502 into data sections in basic so I could try and draw a circle... who knew drawing circles was so ridculously difficult and slow?

Having said that, I do like this stuff in hindsight :)

[pvg]

I liked this piece for the attempt to imagine what using an early personal computer was like and getting it wrong in good and interesting ways - statistically nobody had an Apple I and everything later had BASIC and higher level (i.e. not just monitor) CLIs - that was the big selling point. Later there's a bit about maybe using a decimal FP representation and my first thought was 'no, that's nuts' but your mention of the 800XL sent me to the wikipedia page:

"The first is that all numeric values in [Atari] BASIC are stored in floating-point binary coded decimal (BCD) format"

[cmrdporcupine]

Having spent many hours recently futzing writing code for the 65816, including writing an emulator for a machine based around it, and spending many hours investigating writing a C compiler for it...

I think I might have cured myself of my 6502 nostalgia. I don't want to look at one again for a while.

[markrages]

Were you using a CORDIC algorithm? Bit shifts and adds, no multiplies required.

[djmips]

You don't need CORDIC to draw a circle. BTW, I implemented a CORDIC routine in 6502. It would really benefit from a barrel shifter which the 6502 does not have. https://atariage.com/forums/blogs/entry/3385-atan2-in-6502/

In gist form https://gist.github.com/djmips/29a8fa9099bf92b31a7259da65915...

[pascal_cuoq]

Using a CORDIC algorithm would mean having many iterations to compute trigonometric functions for each drawn point (well, for each 8 points considering the symmetries). A variant of the Bresenham line algorithm for circles lets you draw a circle using only a few operations per 8 points (and the operations are also limited to add and shift):

https://en.wikipedia.org/wiki/Midpoint_circle_algorithm

[keithnz]

no, I had hardcoded lookup tables. I was a teen with no real way to find out information about anything and just applied my high school math to the problem :)