- Assembly 78.8%
- JavaScript 17.8%
- HTML 2%
- C 0.7%
- Makefile 0.7%
| Filename | Latest commit message | Latest commit date |
|---|---|---|
Brooke Vibber
65563b0e79
Noticed that the separate addition for the low 1 bit case was doing some dupe memory loads. Ended up making separate code paths for even and odd values so the even saves two cycles (from 52 down to 50 cycles) and the odd saves 14 cycles (from 69 down to 55 cycles). nice! This gets the XE runtime on default view down from 3m38s to 3m33s, a 5 second runtime improvement |
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| .gitignore | ||
| .mailmap | ||
| atari-asm-xex.cfg | ||
| atari-xex.cfg | ||
| bitmul.s | ||
| fixed.js | ||
| Makefile | ||
| mandel-core.s | ||
| mandel.c | ||
| mandel.h | ||
| readme.md | ||
| sim.html | ||
| sim.js | ||
| tables.js | ||
| testme.js | ||
| todo.md | ||
Mandel-6502
Work-in-progress Mandelbrot fractal viewer for Atari 8-bit home computers. Mostly an excuse to write an integer multiplication routine for the 6502 for practice.
Goals:
- have fun learning 6502 assembly
- make an old machine do something inefficient as efficiently as possible.
- post cool screenshots of low-res fractals
Non-goals:
- maintain anything long-term (but feel free to copy/fork if you want to make major changes!)
Enjoy! I'll probably work on this off and on for the next few weeks until I've got it producing fractals.
-- brooke, january 2023 - december 2024
Current state
Basic rendering is functional, with interactive zoom/pan (+/-/arrows) and 6 preset viewports via the number keys.
The 16-bit signed integer multiplication takes two 16-bit inputs and emits one 32-bit output in the zero page, using the Atari OS ROM's floating point registers as workspaces. Inputs are clobbered.
- 16-bit multiplies are decomposed into 4 8-bit unsigned multiplies and some addition
- an optimized case for squares uses a table of 8-bit squares to reduce the number of 8-bit multiplication sub-ops
- when expanded RAM is available as on 130XE, a 64KB 8-bit multiplication table accelerates the remaining multiplications
- without expanded RAM, a table of half-squares is used to implement the algorithm from https://everything2.com/title/Fast+6502+multiplication
The mandelbrot calculations are done using 3.13-precision fixed point numbers with 6.26-precision intermediates.
Iterations are capped at 255.
The pixels are run in a progressive layout to get the basic shape on screen faster.
There is a running counter of ms/px using the vertical blank interrupts as a timer, used to track our progress. :D
There's a check for cycles in (zx,zy) output when in the 'lake'; if values repeat, they cannot escape. This is a big time saver in fractint.
There's some cute color cycling.
Deps and build instructions
I'm using ca65 as a macro assembler, and have a Unix-style Makefile for building. Should work fairly easily on Linux and Mac. Might work on "raw" Windows but I use WSL for that.
Currently produces a .xex executable, which can be booted up in common Atari emulators and some i/o devices.
Todo
See ideas in todo.md.