Sierpiński Triangle? In My Bitwise and?

https://lcamtuf.substack.com/p/sierpinski-triangle-in-my-bitwise

by guiambros • 1 year ago

217 60 1 year ago

lcamtuf.substack.com

jcul2• 1 year ago

I can't dismiss the cookie popup on this page. After rejecting or accepting cookies it reloads and reappears.

Apologies for a comment not related to the content, but it makes it difficult to read the article on mobile.

jcul2• 1 year ago

Really interesting, and surprising article though!

IceDane• 1 year ago

Same problem here. Firefox on Android.

Jolter• 1 year ago

Same. Safari on iPhone.

adrian_b• 1 year ago

This might be a Firefox problem.

I have never seen it before, but today I have seen it in 3 or 4 sites linked from HN.

What has worked for me is to click "Accept all", then, after the pop-up reappears, click "Only necessary", which makes the pop-up disappear.

Clicking "Only necessary" without clicking before that "Accept all" has not worked. Likewise, clicking multiple times one of those options has not worked.

jrockway• 1 year ago

Substack is kind of a weird site, but this newsletter in particular is worth subscribing to and getting in your email.

peterburkimsher• 1 year ago

Wolfram did a lot of research into cellular automata, and the Sierpinski Triangle kept showing up there too:

https://www.wolframscience.com/nks/

GuB-42• 1 year ago

This one in particular: https://en.wikipedia.org/wiki/Rule_90

jesuslop• 1 year ago

You get those also doing a Pascal triangle mod 2, so a xor. Is a zoom-out fractal as oposed to Mandelbrot set.

anthk2• 1 year ago

True. pas.f in Forth

    : .r u.r ;
    : position  ( row -- )  cr  33 swap 2 *  - spaces  ;
    : pas ( 0 ... 0 -- 0 ... 0 )    0 >r begin
    over + >r  dup 0= until
    begin  r> dup while  dup 4 .r  repeat  ;
    : pass  ( -- )    0 1 0    18 0 ?do  dup position  >r  pas  r>  1+  loop      drop  ;
    : pax  ( 0 ... 0 -- )  drop begin 0= until ;
    : pascal  ( -- )  pass pax ;

    pascal
    cr

The same mod2:

    : .r u.r ;
    : position  ( row -- )  cr  33 swap 2 *  - spaces  ;
    : pas ( 0 ... 0 -- 0 ... 0 )    0 >r begin
     over + >r  dup 0= until
     begin  r> dup while  dup 2 mod 4 .r  repeat  ;
    : pass  ( -- )    0 1 0    18 0 ?do  dup position  >r  pas  r>  1+  loop     drop  ;
    : pax  ( 0 ... 0 -- )  drop begin 0= until ;
    : pascal  ( -- )  pass pax ;

    pascal
    cr

A Forth for people in a hurry:

     git clone https://github.com/howerj/subleq
     cd subleq
     sed -i 's,0 constant opt.control,1 constant opt.control,g' subleq.fth
     gmake subleq
     ./subleq subleq.dec < subleq.fth > new.dec
     ./subleq new.dec < pas.f

kragen4• 1 year ago

Output from `cr pascal` in GForth:

                                    1
                                  1   1
                                1   0   1
                              1   1   1   1
                            1   0   0   0   1
                          1   1   0   0   1   1
                        1   0   1   0   1   0   1
                      1   1   1   1   1   1   1   1
                    1   0   0   0   0   0   0   0   1
                  1   1   0   0   0   0   0   0   1   1
                1   0   1   0   0   0   0   0   1   0   1
              1   1   1   1   0   0   0   0   1   1   1   1
            1   0   0   0   1   0   0   0   1   0   0   0   1
          1   1   0   0   1   1   0   0   1   1   0   0   1   1
        1   0   1   0   1   0   1   0   1   0   1   0   1   0   1
      1   1   1   1   1   1   1   1   1   1   1   1   1   1   1   1
    1   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   1
   1   1   0   0   0   0   0   0   0   0   0   0   0   0   0   0   1   1 ok

By changing `4 .r` to `bl + dup dup dup emit emit emit emit` I get this:

                                      !!!!
                                    !!!!!!!!
                                  !!!!    !!!!
                                !!!!!!!!!!!!!!!!
                              !!!!            !!!!
                            !!!!!!!!        !!!!!!!!
                          !!!!    !!!!    !!!!    !!!!
                        !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
                      !!!!                            !!!!
                    !!!!!!!!                        !!!!!!!!
                  !!!!    !!!!                    !!!!    !!!!
                !!!!!!!!!!!!!!!!                !!!!!!!!!!!!!!!!
              !!!!            !!!!            !!!!            !!!!
            !!!!!!!!        !!!!!!!!        !!!!!!!!        !!!!!!!!
          !!!!    !!!!    !!!!    !!!!    !!!!    !!!!    !!!!    !!!!
        !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
      !!!!                                                            !!!!
    !!!!!!!!                                                        !!!!!!!! ok

But this is not using bitwise AND, just the Pascal's triangle approach. (Interestingly, you can reformulate that as a neighborhood-2 2-state 1-dimensional cellular automaton pretty easily; it occurs in a couple of different guises in Wolfram's catalog.)

Here's an ASCII-art version that uses AND as Michał describes:

    32 value size  : line cr size 0 do dup i and if bl else [char] # then dup emit emit loop drop ;
    : pasand size 0 do i line loop ;

Running `pasand` then yields this:

    ################################################################
    ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  
    ####    ####    ####    ####    ####    ####    ####    ####    
    ##      ##      ##      ##      ##      ##      ##      ##      
    ########        ########        ########        ########        
    ##  ##          ##  ##          ##  ##          ##  ##          
    ####            ####            ####            ####            
    ##              ##              ##              ##              
    ################                ################                
    ##  ##  ##  ##                  ##  ##  ##  ##                  
    ####    ####                    ####    ####                    
    ##      ##                      ##      ##                      
    ########                        ########                        
    ##  ##                          ##  ##                          
    ####                            ####                            
    ##                              ##                              
    ################################                                
    ##  ##  ##  ##  ##  ##  ##  ##                                  
    ####    ####    ####    ####                                    
    ##      ##      ##      ##                                      
    ########        ########                                        
    ##  ##          ##  ##                                          
    ####            ####                                            
    ##              ##                                              
    ################                                                
    ##  ##  ##  ##                                                  
    ####    ####                                                    
    ##      ##                                                      
    ########                                                        
    ##  ##                                                          
    ####                                                            
    ##                                                               ok

dvt2• 1 year ago

Just a heads up, all (binary?) logical operators produce fractals. This is pretty well-known[1].

[1] https://icefractal.com/articles/bitwise-fractals/

wang_li• 1 year ago

The change rate in binary notation is fractal.

Timwi• 1 year ago

Ask yourself why you added the “pretty well-known” phrase, and consider xkcd 1053.

marginalia_nu• 1 year ago

It would be interesting to see how this generalizes to other bases.

Base 3 has nearly 20,000 operators, of which 729 are commutative.

dvt2• 1 year ago

Yeah, I'm pretty sure as long as you have symmetry somewhere (e.g. a commutative operation), you'll get self-similar patterns.

eru2• 1 year ago

That's more or less, because binary numbers are already fractal.

zX41ZdbW• 1 year ago

Sierpinski also sounds nice in music. Examples here: https://github.com/ClickHouse/NoiSQL

gjm115• 1 year ago

Here's a possibly-too-highbrow explanation to complement the nice simple one in the OP.

"As everyone knows", you get a Sierpinski triangle by taking the entries in Pascal's triangle mod 2. That is, taking binomial coefficients mod 2.

Now, here's a cute theorem about binomial coefficients and prime numbers: for any prime p, the number of powers of p dividing (n choose r) equals the number of carries when you write r and n-r in base p and add them up.

For instance, (16 choose 8) is a multiple of 9 but not of 27. 8 in base 3 is 22; when you add 22+22 in base 3, you have carries out of the units and threes digits.

OK. So, now, suppose you look at (x+y choose x) mod 2. This will be 1 exactly when no 2s divide it; i.e., when no carries occur when adding x and y in binary; i.e., when x and y never have 1-bits in the same place; i.e., when x AND y (bitwise) is zero.

And that's exactly what OP found!

coderatlarge4• 1 year ago

i really love the result you quote about the carries. do you know where it has been applied by any chance?

gjm115• 1 year ago

I don't know of applications offhand, sorry. For me it's in the "appreciated for its own sake" category :-).

ethan_smith• 1 year ago

This elegantly explains why (x & y) == 0 produces Sierpinski triangles: it's equivalent to checking whether (x+y choose x) mod 2 equals 1, directly connecting bitwise operations to binomial coefficients.

tomrod• 1 year ago

I prefer mine au naturale 3-adic.

https://m.youtube.com/watch?v=tRaq4aYPzCc

Just kidding. This was a fun read.

kragen4• 1 year ago

The 31-byte demo "Klappquadrat" by T$ is based on this phenomenon; I wrote a page about how it works a few years ago, including a working Python2 reimplementation with Numpy: http://canonical.org/~kragen/demo/klappquadrat.html

I should probably update that page to explain how to use objdump correctly to disassemble MS-DOG .COM files.

If you like making fractal patterns with bitwise arithmetic, you'll probably love http://canonical.org/~kragen/sw/dev3/trama. Especially if you like stack machines too. The page is entirely in Spanish (except for an epilepsy safety warning) but I suspect that's unlikely to be a problem in practice.

userbinator• 1 year ago

Sierpinski triangles are definitely a common sight in demoscene productions, to the point that they're acceptable in the smaller sizes, but others will think you're not good enough if that's all you do for a 64k or above entry.

marvinborner• 1 year ago

Very cool! This basically encodes a quad-tree of bits where every except one quadrant of each subquadrant recurses on the parent quad-tree.

The corresponding equivalent of functional programming would be Church bits in a functional quad-tree encoding \s.(s TL TR BL BR). Then, the Sierpinski triangle can be written as (Y \fs.(s f f f #f)), where #f is the Church bit \tf.f!

Rendering proof: https://lambda-screen.marvinborner.de/?term=ERoc0CrbYIA%3D

zabzonk• 1 year ago

I draw these with paper and pen when I am extremely bored in meetings.

susam• 1 year ago

I’d like to share some little demos here.

Bitwise XOR modulo T: https://susam.net/fxyt.html#XYxTN1srN255pTN1sqD

Bitwise AND modulo T: https://susam.net/fxyt.html#XYaTN1srN255pTN1sqN0

Bitwise OR modulo T: https://susam.net/fxyt.html#XYoTN1srN255pTN1sqDN0S

Where T is the time coordinate. Origin for X, Y coordinates is at the bottom left corner of the canvas.

You can pause the animation anytime by clicking the ‘■’ button and then step through the T coordinate using the ‘«’ and ‘»’ buttons.

kragen4• 1 year ago

Gorgeous!

msarnoff• 1 year ago

Munching squares!

ttoinou• 1 year ago

Thank you for sharing. The third one has some kind of trippy 3d effect in the first seconds

Recursing• 1 year ago

Shadertoy link: https://www.shadertoy.com/view/MllcW2

And, xor, and or are red, green and blue

anyfoo• 1 year ago

Ah. Is that why LFSRs (linear feedback shift registers) and specifically PRBS generators (pseudo-random binary sequences) produce Sierpinski triangles as well?

PRBS sequences are well-known, well-used "pseudo-random" sequences that are, for example, used to (non-cryptographically!) scramble data links, or to just test them (Bit Error Rate).

I made my own PRBS generator, and was surprised that visualizing its output, it was full of Sierpinski triangles of various sizes.

Even fully knowing and honoring that they have no cryptographic properties, it didn't feel very "pseudo-random" to me.

modeless2• 1 year ago

Try this one liner pasted into a Unix shell:

  cc -w -xc -std=c89 -<<<'main(c){int r;for(r=32;r;)printf(++c>31?c=!r--,"\n":c<r?" ":~c&r?" `":" #");}'&&./a.*

It used to be cooler back when compilers supported weird K&R style C by default. I got it under 100 characters back then, and the C part was just 73 characters. This version is a bit longer but works with modern clang. The 73-character K&R C version that you can still compile today with GCC is:

  main(c,r){for(r=32;r;)printf(++c>31?c=!r--,"\n":c<r?" ":~c&r?" `":" #");}

Terr_• 1 year ago

Instructions unclear, machine rooted. :p

modeless2• 1 year ago

Hey, at least it's not doing `curl | bash` like some people's installers do. It's only 109 characters, you can review that right? :-P

_7acn• 1 year ago

Sierpinski pirated it from Razor 1911 :)

lenerdenator• 1 year ago

It's more likely than you think.

ChuckMcM• 1 year ago

Y'all would really like https://www.gathering4gardner.org/ :-)

I tend to like lcamtuf's Electronics entries a bit better (I'm an EE after all) but I find he has a great way of explaining things.

msephton• 1 year ago

I first saw these sorts of bitwise logic patterns at https://twitter.com/aemkei/status/1378106731386040322 (2021)

fiforpg• 1 year ago

the magic is the positional numeral system

— of course. In the same way the (standard) Cantor set consists of precisely those numbers from the interval [0,1] that can be represented using only 0 and 2 in their ternary expansion (repeated 2 is allowed, as in 1 = 0.2222...). If self-similar fractals can be conveniently represented in positional number systems, it is because the latter are self-similar.

pacaro• 1 year ago

There are so many ways to produce sierpinski gaskets.

It you specify n points and the pick a new point at random, then iteratively randomly select (uniformly) one of the original n points and move the next point to the mid point of the current point and the selected point. Coloring those points generates a sierpinski triangle or tetrahedron or whatever the n-1 dimensional triangle is called

linschn• 1 year ago

That's called a simplex :)

The same as in the simplex algorithm to solve linear programming problems.

CrazyStat• 1 year ago

I programmed this on my TI-83 back in the day and spent many hours watching it generate triangles during boring classes.

You can generate many other fractals (e.g. fern shapes) in a similar way, though the transformations are more complicated than “move halfway to selected point”.

deadfoxygrandpa• 1 year ago

yes, those are called iterated function systems (IFS) fractals

tikili• 1 year ago

Munching squares: https://tiki.li/show/#cod=VYxLCoAwDET3PcWsFWql4s7D1Fo/oBZqkf...

immibis• 1 year ago

basically, whenever a shape contains 3 connected couples of itself, you get a deformed Sierpinski triangle.

gitroom• 1 year ago

been down the bitwise fractal rabbit hole more times than i can count and honestly, i never get tired of these patterns - you think people start seeing shapes like this everywhere after a while or is that just me

tpoacher• 1 year ago

I reached a similar result when researching all possible "binary subpixel" configurations that would give a pixel its fuzzy value. Arranging the configurations in ascending order row-wise for one pixel and column-wise for the other, performing an intersection between the two pixels, and plotting against their resulting fuzzy value results in a sierpinski triangle.

(if interested, see fig 4.3, page 126 of my thesis, here: https://ora.ox.ac.uk/objects/uuid:dc352697-c804-4257-8aec-08...)

Cool stuff. Especially the bottom right panel, you might not have expected that kind of symmetry in the intersection when looking at the individual components.

Sierpiński Triangle? In My Bitwise and?

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