More progress on the Finite Projective Plane (incidence matrix) generation from last week. There already exists an algorithm to generate boards of order p+1 where p is prime. It is stateless, so with CUDA we can generate huge boards in seconds since all you need is the x, y position and board size. 258x258 under 3s!

However, p+1 isn’t the only sequence. It seems by our observations that the fermat numbers also generate valid boards, using our “naïve” algorithm.

Unfortunately 3x3, 5x5, and 17x17 might not contain all the nuggets of generality to find a nice algorithm like the p+1, so we’re gonna generate the next up: 257x257. We’ve been improving the naïve algorithm since it is too slow. (The resulting image would be 65793x65793)

• Rather than allocating the 2d boolean grid, we represent where the true elements would be using row and column indexes. This is okay because of the constraint which limits how many true elements can be in a row/column
  • benefit 1 — less memory usage: “O(2n)” vs O(n²) ((for 257x257: 129MiB vs 4GiB))
  • benefit 2 — faster column-major lookups (flamegraph spent a lot of time sitting in iterators)
  • overall speedup: about 2.7x
• Speed up index lookup with binary search
  • The index list is sorted by nature. To exhaustively check a dot is valid, it checks n² spots in 2 lists of size n. Slightly more expensive than the grid given the 2 index lists. Rather than slice::contains, use slice::binary_search(...).is_ok()
  • overall speedup: about 2.1x

Next steps:

• Assume a square grid and exploit its diagonal symmetry to treat row lookups as column lookups
• Use multi threading to gain a partial speedup
  • Essentially if row 1 is 50% completed, row 2 can be up to 50% completed.
  • I think you get different speeds depending whether the threads and symmetry folds are both row/column major or one is row-major and the other is column-major. My gut says both need to be aligned because there’s less waiting involved.

Apparently generating “Finite Projective Planes”. For context on how I got here, I went camping with my family and brought the game Spot It. My brother was analyzing it and came up with the same type of pattern.

When we got home he made a python script to generate these boards, but it was quite slow, so he half joked asking me to rewrite it in Rust.

I kinda struggled a bit since I didn’t fully understand what it was doing. Near the end I even got a segfault using safe code😃! (i was spawning a thread with a large stack size, and allocating huge slices on its stack, rather than you know… boxing the slice Lol.) When I finally got it working, it ended up being in the ballpark of a 23x speedup. Not bad for changing the language choice!

There’s lots of room for improvement left for sure. The algorithm could benefit with some running statistics about cols/rows and the algorithm itself is quite naïve and could maybe be improved too :P

If they aren’t equal, there should be a number in between that separates them. Between 0.1 and 0.2 i can come up with 0.15. Between 0.1 and 0.15 is 0.125. You can keep going, but if the numbers are equal, there is nothing in between. There’s no gap between 0.1 and 0.1, so they are equal.

What number comes between 0.999… and 1?

(I used to think it was imprecise representations too, but this is how it made sense to me :)

Imagine they have an internal tool to check if the hash exists in their database, something like

"SELECT user FROM downloads WHERE hash = '" + hash + "';"

You set the pdf hash to be 1'; DROP TABLE books;-- they scan it, and it effectively deletes their entire business lmfaoo.

Another idea might be to duplicate the PDF many times and insert bogus metadata for each. Then submit requests saying that you found an illegal distribution of the PDF. If their process isn’t automated it would waste a lot of time on their part to find the culprit Lol

I think it’s more interesting to think of how to weaponize their own hash rather than deleting it

I was thinking that the user intentionally chose their distro, because of the Ubuntu character.

Cool, more free stuff

Arch, you want more free stuff faster

Not again!

Debian, you want to set and forget, so any updates that do come up are still a nuisance

/dev/sdX is a file, and both dd, cat can read files in full. You can even try something like zstd to compress it too.

One of the nice things about dd though is you can see the progress with --status=progress

I think it is so that the subvolume can be mounted with different options. You can of course have a mixed layout which might be more convenient, so that say root and home subvolumes mount with the same options, but swap mounts with different options. And the top level never gets mounted at all.

toplevel (not mounted)
+-- @ (subvolume mounted on /)
    +-- home (subvolume, looks like a folder, same mount options as @)
    +-- usr (folder, gets snapshotted by @)
    +-- ...
+-- @swap (subvolume with different options, mounted on /swap)

I set mine up with a purely flat layout so I haven’t verified this is true, but it sounds reasonable.

Here’s the documentation I was looking at:

https://web.archive.org/web/20220103010302/https://btrfs.wiki.kernel.org/index.php/SysadminGuide#Flat

Screenshot woulda been better just so everyone sees the same thing lol. I wasn’t sure what it would look like because on browser it highlighted some things green, and on Voyager it seems to highlight 4+ space indented as gray. No clue what is going on there :D

vim with :set virtualedit=all gets pretty close being able to “paint” text anywhere… unfortunately i was on my phone and didn’t think to use it

o Windows 10
|
o Linux Mint
|
|\__
|   \
|    o Manjaro KDE
|    |
o Fedora KDE
|    |\__
|    |   \
x    |    o Windows 11
     |    o Windows 11 + Arch Linux
     |    |
     o Arch Linux
     |    |
     |    |
     |    o Windows 11 + Debian KDE
     |    |

hopefully it renders well on your client :D

Woahh thats so cool!!

I think your QMK config counts (for now;)) What are some useful things you’ve changed?

Yeah, im a bit worried about vim binds for alternative layouts as well. I think some people use a layer mod to keep normal mode as QWERTY (or a “normal mode” layer) but insert mode uses their regular layout. Others apparently use their non-qwerty layout for everything (but i guess change hjkl). Apparently it’s not too bad… but probably depends on the person.

The clamps lol, i love it!

I’ve had this type of itch to keyboardize my workflow more. I learned about colemak keyboard mods, and started following the rabbit hole haha. Did you design your keyboard pcb too? or just wrote custom firmware?

Ooo cool, thanks for sharing!

Not having Paint.NET sucked when I switched to Linux. I got very used to it and that was the one I missed most… it took a few years bouncing between programs but I’m happy with Krita now. GIMP just never clicked for me unfortunately.

I sometimes think about making a Paint.NET clone for linux but i have too many other projects and hobbies i wanna do instead yk

XWayland normally runs x11 apps seamlessly (more or less) in Wayland

XWayland rootful spawns a window which is like a virtual monitor running a full x11 session inside it. You spawn apps inside of the window using the DISPLAY variable