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Wednesday, 2nd July 2025

Mandelbrot in x86 assembly by Claude. Inspired by a tweet asking if Claude knew x86 assembly, I decided to run a bit of an experiment.

I prompted Claude Sonnet 4:

Write me an ascii art mandelbrot fractal generator in x86 assembly

And got back code that looked... like assembly code I guess?

So I copied some jargon out of that response and asked:

I have some code written for x86-64 assembly using NASM syntax, targeting Linux (using system calls for output).

How can I run that on my Mac?

That gave me a Dockerfile.

I tried running it on my Mac and... it failed to compile.

So I fired up Claude Code (with the --dangerously-skip-permissions option) in that directory and told it what to run:

Run this: docker build -t myasm .

It started crunching. It read the errors, inspected the assembly code, made changes, tried running it again in a loop, added more comments...

Terminal window showing code diff for Mandelbrot fractal program. • Now I need to fix the Mandelbrot iteration logic as well. The current fixed-point arithmetic has issues: • Read(program.asm) └ Read 30 lines (Ctrl+r to expand) • The Mandelbrot iteration logic also has issues with fixed-point arithmetic. Let me fix this too: • Update(program.asm) └ Updated program.asm with 18 additions and 12 removals showing assembly code diff with line numbers 63-91, including removed lines marked in red for fixed point multiplication calculations and added lines in green with 64-bit arithmetic conversions, comments describing z_real and z_imag calculations, and mandel_done logic checks.

...and eventually produced an ASCII art image of a fractal! Claude Code proudly declared:

Success! The Docker container ran and generated a Mandelbrot set visualization using ASCII characters. The output shows all @ symbols, which indicates the algorithm is working but all points are inside the set (high iteration count). The program compiled and executed successfully on x86_64 architecture via emulation.

Yeah... I was not satisfied with an image that was entirely @ symbols! I said:

That is a bad result - it is just @ signs, I cannot see the fractal

Claude made a few more changes and gave me the result I wanted:

A terminal window showing a pleasing ASCII art Mandelbrot set, zoomed to the expected level

Here's the finished assembly code, the Dockerfile to run it on a Mac and the full transcript of the Claude Code session that got it there.

# 4:35 am / mandelbrot, ai, generative-ai, llms, ai-assisted-programming, anthropic, claude, vibe-coding, claude-code

On two occasions I have been asked, — "Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out ?" In one case a member of the Upper, and in the other a member of the Lower, House put this question. I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.

— Charles Babbage, Passages from the Life of a Philosopher, 1864

# 3:04 pm / charles-babbage

2025 » July

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