WriteUp: 16 Bytes of x86 that turn Matrix rain into sound
hellmood.111mb.de87 points by HellMood 8 hours ago
87 points by HellMood 8 hours ago
I thought this was going to convert a matrix rain into sound but it does visual and sound. Amazing. And it is almost like a decent track, music is going round in my head now.
Is this a program or a secret key that unlocks a beast? Not sure!
Quite incredible. This comment is larger.
It must be magic. I don't believe it's possible in such short snippet of code.
It kind of still is! The pure sound shouldnt even sound like that, so i have to still dig around memory configurations and initalizations (graphics card wise) to 100% explain why it sounds a tad different than it should.
How does the sierpinski fractal relate to the rain effect?
TLDR: Each time step, another sierpinski triangle line is a) played on the speaker b) drawn to the screen with stepsize of 56. You can sense the motion, but not really see it, since it's 8192 "pixels wide" but one line of chars is just 80 bytes. One a much much much bigger screen, you could see the triangle. Or, if you dont "skip pixels" and draw it all at once, you would see it as well. In fact, i did a version at the very the same party that does that, but the specific sound gets lost on that one
https://www.pouet.net/prod.php?which=106206 https://www.youtube.com/watch?v=OVk-iP93ZEs
"wake up! 16b" (Outline Demoparty, May 2026, Ommen, NL) is a 16-byte MS-DOS production that uses video memory to calculate a Sierpinski fractal and play it as audio.
Video: https://youtu.be/MvycyU-kLjg | Pouet: https://www.pouet.net/prod.php?which=106210
The 16-Byte Code:
int 10h ; Init Video Mode 0
mov bh, 0xb8 ; Setup VRAM segment
mov ds, bx
L: lodsb ; Load [SI] to AL, inc SI
sub si, 57 ; Move pointer backward
xor [si], al ; Cellular Automaton
out 61h, al ; PC Speaker output
jmp short L ; Infinite loop
2. The Fractal (Rule 60): If this loop used `add`, it would create a binomial prefix sum:
A^(p)[k] = 2 \* C(k+p, p-1) mod 256
Cell^(p)[k] = Cell^(p-1)[k] XOR Cell^(p)[k-1]
P1: X X X X X X X X
P2: . X . X . X . X
P3: X . . X X . . X
P4: . . . X . . . X
P5: X X X . . . . X
P6: . X . . . . . X
P7: X . . . . . . X
4. The -56 Byte Step: The pointer's net movement is -56 bytes per loop. - Visuals: On an 80-byte wide grid, this offset shears the fractal diagonally into 10 evenly spaced, ascending vertical pillars. - Audio: 56 does not divide the 64KB segment evenly, requiring 8,192 steps (7 full wraps) to complete a cycle. Doubling the macro-cycle halves the fundamental frequency, dropping the audio exactly one octave.
5. Hardware Quirks: The theoretical math expects zeroed memory, but the XOR operation violently collides with the BIOS's 0x20/0x07 initialization. This mutates the pure triangles into a cascade of pseudo-random ASCII glyphs. Because it relies entirely on raw RAM states, the visual and auditory output is highly sensitive to the specific machine or emulator, turning a simple mathematical quirk into a unique audiovisual fingerprint.
Well done! What were you exploring that seeded this in your mind?
Actually a) polymorphic asm instructions, like "add [bx+si],al" which is 0x0000 b) jumping into middle of instructions to save bytes and reuse opcodes
In hundreds of tiny experiments, this one stuck out, just by the sound of it. When i unfolded what's left and removed "the rest" i had a hard time to grasp what's really going on. i myself didnt expect that the explanation would go this deep for just these few bytes xD