social.noyu.me

these last few weeks, @lynn and me have been working on a c compiler for uxn, based on rui ueyama's “chibicc”. it's been a lot of fun! it's such a cute little vm… assembly for this tiny stack machine involved so many little puzzles.

i made a demo https://github.com/lynn/chibicc/blob/uxn/examples/star.c :3

the fact it's a stack machine makes it really fun to write (or generate!) assembly for. you never have to remember register numbers, all the inputs and outputs are implicit. the magic of concatenative programming~

one of the challenges was that uxn doesn't have signed integer operations, but they're essential for c code, so i had to write some little helper routines that emulate signed operations. for example, this does sign extension (char->int conversion):

#80 ANDk EQU #ff MUL SWP

the single most complicated thing to emulate was, believe it or not, argc and argv: https://github.com/lynn/chibicc/blob/uxn/routines/argc_argv.tal

don't let that scare you though, most of the compiler isn't anywhere near that complex, hehe

writing c code with this compiler also involves a lot of problem solving. there's no floats, no 32-bit integers, almost no C runtime, and only 64KiB of ROM space. the compiler can't do much optimisation of your code. you'll have to be creative!

related: https://social.noyu.me/@hikari/statuses/01H2G44V6QJ7BB9Y3J25QCEPB8

btw, uxn/varvara is a really impressive vm. what amazes me is how small it manages to keep its api surface while still providing everything you could want: graphics, sound, mouse input, keyboard input, gamepad input, file i/o, a real-time clock, stdin, stdout and stderr!

it does all of that while having far fewer api entrypoints than posix or wasi or the browser or any api you can think of, and they're all defined in such simple and constrained ways that there's very little room for incorrect implementations (though still some: i have found bugs)

so i think uxn apps will have fantastic portability. better even than famicom roms, and yet they can do more!

it'll never replace wasm: apps can only use 16-bit integers, a 64KiB address space and 2-bit color. but that's still a whole universe of creative potential. i love it.

the limits aren't without advantages: it's a universe where you can store your whole app collection on a floppy disk, or run it on a gba…

i am pleased to announce oneko-uxn: a port of oneko-sakura to #uxn. this is a version of the classic software ”Neko”! 🐈🖱

https://github.com/hikari-no-yume/oneko-uxn

日本語版も有ります。

this all was made possible with chibicc-uxn, the c compiler for uxn that @lynn and i have worked on together.

have fun!

i painstakingly preserved the structure, comments, and feature set to the greatest extent possible… parts of this codebase are several years older than i am, and i wanted to respect the history. it's the most faithful port of this program that is possible, i think!

i found a bug in oneko-uxn: the 16-bit Euclidean distance calculation can overflow even for 8-bit inputs :(

but @lynn found a great alternative: the average of the L1 norm and L∞ norms is within ~6% of the Euclidean distance, and way easier to compute!

https://github.com/hikari-no-yume/oneko-uxn/commit/060bc664e647e3ea6d1362fa5d882c1d1b95a87c

this has to be a known algorithm, right? it's so much easier to compute on a system with only integer arithmetic, and gets amazingly close to the right answer…

smol neko window (upcoming feature teaser)

new version of oneko-uxn. two fixes + two new features.

now the window size can be customized.

https://github.com/hikari-no-yume/oneko-uxn/releases/tag/1.2.sakura.5.uxn.2

日本語版も有ります。

#uxn

@lynn @neauoire (cc)

this will probably be the final version, fwiw. i wasn't intending to have more than one version, but i wanted to fix that movement vector bug, and that made it clear the premise i had for not allowing window size customisation was wrong, so i added that too

oops, i forgot to recompile when i bumped the version number. i fixed that now, but this means someone out there might have a copy of the rom that reports a lower version number, but has the new features and fixes 👻

@hikari

In another time this would've been the basis for a creepypasta.

@hikari 👀

@hikari @lynn What's the red curve represent?

@cr1901 @hikari @lynn it's the direction of the cat :)

@neauoire @hikari @lynn The cat has flower on the brain, apparently :o...

@cr1901 @lynn

0 ≤ x ≤ 2π

cx = cos(x)
sx = sin(x)

i plot a point at (cx, sx)

interpreting (cx, sx) as a vector from (0, 0), the euclidean distance is always going to be 1, right

i then calculate the same distance with our approximation, and plot a point at (cx * distance, sx * distance)

so the red line shows how far it strays from euclidean distance at various angles

@cr1901 @lynn you can see that at 0°, 90°, 180° and 270°, there's no difference, which should be intuitive considering that these are exactly the directions for which euclidean distance, L1/manhattan distance and L∞/chebyshev distance are identical, so an average of these last two should be the same as the first of these

@hikari

That is so lovely! Incant wait to download it when I get home.

I remember playing with a version of Neko on my Mac SE circa 1990. Neko stayed on the desktop and followed the mouse everywhere.
Actually, I believe it came on Bob Levitus' book (and floppy), "Stupid Mac Tricks." It flickered a lot, bit was cute. 😁

@RL_Dane I had many old PDAs growing up. my first experience of Neko was a PalmOS port <3

@hikari

Ah, I missed that one. That would've been neat.

A lot more wholesome than that bizarre app where you give a monkey crack cocaine and he does unspeakable things to a bunny.

Some of those PalmOS apps were deranged, lol

@hikari @lynn ah! I knew it. When you said you were working on an unannounced port this porting, I crossed my fingers it'd be neko <3 amazing.

@neauoire @lynn wow, that's some coincidence! but to be honest i was slightly surprised when i couldn't find an existing port to uxn. it felt obvious, hehe. I'm glad you like it!

my first exposure to Neko was playing a PalmOS port of it as a kid, around two decades ago, so i've had a lifelong fondness for it at this point.

@hikari @lynn Coincidentally I also recently used the old neko bitmaps for a personal project! If anyone wants code snippets for displaying them on Wayland using pixman, let me know. It is straight-forward, but pixman enforces a minimum stride and a minimum buffer size, which means you can't use the original sizes of the bitmap sprites. I ended up stitching them together into a texture atlas.

@hikari I've been thinking about adding 32-bit int support (by deferring to the library that's linked on the README), but I don't want to start a new project rn.

So if either you or @lynn intend to add it at some point, I leave it to you.

@cr1901 @lynn i can't really speak for lynn but i think the feeling is that we'd rather not have something requiring such heavy runtime support. it's not something most applications need, you should only use it sparingly, and you can just call it via asm, or maybe via improved extern support in the future

@cr1901 @lynn with that said i have wondered myself about writing a float library, but i probably wouldn't integrate that into the compiler for the same reason

@hikari Whenever I can, in the morning usually, I go over the changes you two made over chibicc. It has taught me a lot. I really appreciate you working on this, it even helped me elucidate a few questions I had about how C worked.

@neauoire thank you! i'm glad it's been so interesting. re: how C works, one reason i've enjoyed this project is that i've been able to practically apply a lot of my more obscure knowledge about C… for example, the rules about what type (signed)a + (unsigned char)b should use

@hikari Where do you get the answers to these sorts of question, do you have a sort of reference? If so, could I have a link to it?

@neauoire a lot of this stuff i've just gradually accumulated in my head over time so i don't know how i first learned most of these things, but i do have references i use to check my knowledge:

• the C standard isn't available for free, sadly, but you can usually find a copy of the last draft before a particular published version

• https://en.cppreference.com/w/c is the best online C documentation I know about

@neauoire my power is really in knowing what info exists, and what it is called, so i know what to look up. i know some magic keywords, like “usual arithmetic conversion” and “integer promotions”

@hikari @neauoire There's also #c on Libera, but...

Look, I've not experienced this personally since I'm not a regular, but I've heard in the past that it's full of egos who like wielding minutiae of C standard as a sort of cudgel/way to feel superior (Just like emulation lmao).

@neauoire @hikari Stack Overflow also is _filled_ with Q and A about "what does the C Standard say about X".

However many answers you think there are about the C standard on SO, multiply it by 10.

So that's ends up being a good way to jump into the parts of the spec you care about :D!

@cr1901 @neauoire C is one of those complex things that people on the internet are often wrong about, so my one piece of advice is to look for answers that tell you what part of the standard to check, and then check that part of the standard, rather than trusting the answer itself