diff --git a/readme.md b/readme.md index f297d60..873793f 100644 --- a/readme.md +++ b/readme.md @@ -14,18 +14,15 @@ 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 - december 2024 +-- brooke, january 2023 - february 2024 ## Current state -Basic rendering is functional, with interactive zoom/pan (+/-/arrows) and 4 preset viewports via the number keys. +Basic rendering is functional, but no interactive behavior (zoom/pan) or benchmarking is done yet. -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 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. -* 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 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. The mandelbrot calculations are done using 4.12-precision fixed point numbers. It may be possible to squish this down to 3.13. @@ -33,18 +30,17 @@ 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 +## Next steps -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. +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 some cute color cycling. +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) ## 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 diff --git a/todo.md b/todo.md index 1281de7..4aaedc0 100644 --- a/todo.md +++ b/todo.md @@ -2,13 +2,14 @@ things to try: * patch the entire expanded-ram imul8xe on top of imul8 to avoid the 3-cycle thunk penalty :D +* optimize out a store/load with mul8_add16 and mul8_add24 + * try 3.13 fixed point instead of 4.12 for more precision * can we get away without the extra bit? * y-axis mirror optimization * 'wide pixels' 2x and 4x for a fuller initial image in the tiered rendering - * maybe redo tiering to just 4x4, 2x2, 1x1? * extract viewport for display & re-input via keyboard