From ed79c80b167607f0c59d7c8f33569f9bf3e981f5 Mon Sep 17 00:00:00 2001 From: Brooke Vibber Date: Mon, 30 Dec 2024 16:50:25 -0800 Subject: [PATCH] update readme --- readme.md | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-) diff --git a/readme.md b/readme.md index 873793f..f297d60 100644 --- a/readme.md +++ b/readme.md @@ -14,15 +14,18 @@ Non-goals: 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 - february 2024 +-- brooke, january 2023 - december 2024 ## Current state -Basic rendering is functional, but no interactive behavior (zoom/pan) or benchmarking is done yet. +Basic rendering is functional, with interactive zoom/pan (+/-/arrows) and 4 preset viewports via the number keys. -The 16-bit signed integer multiplication works; it 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. +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. -The main loop is a basic add-and-shift, using 16-bit adds which requires flipping the sign of negative inputs (otherwise you'd have to add all those sign-extension bits). Runs in 470-780 cycles depending on input. +* 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 4.12-precision fixed point numbers. It may be possible to squish this down to 3.13. @@ -30,17 +33,18 @@ Iterations are capped at 255. The pixels are run in a progressive layout to get the basic shape on screen faster. -## Next steps +There is a running counter of ms/px using the vertical blank interrupts as a timer, used to track our progress. :D -Add a running counter of ms/px using the vertical blank interrupts as a timer. This'll show how further work improves it! +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. -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. - -I may be able to do a faster multiply using tables of squares for 8-bit component multiplication. -(done) +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`. \ No newline at end of file