Building a RAR compressor using LLMs: A 5-week reverse-engineering project
By
davidsong
A five-star bake. Worth schmearing, sharing, saving.
Summary
A developer documents their experience using LLMs (OpenAI Codex 5.5 and Claude Opus 4.7) to reverse-engineer the RAR compression format and build a RAR compressor from scratch. What would normally take 5 years of work was accomplished in 5 weeks of evenings and weekends, costing roughly £40 in subsidized tokens and producing 55k lines of code. The project pushed the limits of what LLMs can do for complex reverse-engineering tasks, though the author notes the code is "slop" and not particularly fast.
Key quotes
· 3 pulledA RAR compressor for every version of RAR ought to have taken about 5 years, which is why nobody has ever bothered. Today, it takes 5 weeks of evenings and weekends, clanking OpenAI Codex 5.5 and Claude Opus 4.7, and cost roughly £40 in (heavily subsidised) tokens.
Yes it's 55k lines of slop, no it's not that fast, and it almost earned me an OpenAI ban. But it works.
I've done a few different reverse-engineering projects with LLMs, and figured it's time to push the clankers to their limits.
You might also wanna read
Developer Builds Mac and iOS Dictation App with AI Assistance
A developer shares their experience building a Mac and iOS dictation app using Claude's assistance, despite initial skepticism about whether
news.ycombinator.com·1d ago
How AI-Assisted Coding Enabled Shipping a Go Service Without Prior Language Expertise
A technical architect shares his experience using AI tools (like GitHub Copilot and ChatGPT) to build a working service in Go, a programming
How AI Coding Models Are Outpacing Our Context Control Systems
The author reflects on how their coding process has evolved over the past year while using AI models to write code. They note that while mod
Vibe Coding Explained: How AI Lets You Create Software by Describing What You Want
Vibe coding is a method of creating computer code using artificial intelligence where users describe what they want built rather than writin
techlearning.com·3d ago
Vibeocus Lens: A developer tool that streams live DOM data from browser to AI coding agents
Vibeocus Lens is a developer tool created by solo maker Ekhtiram that solves a common friction point in "vibe-coding" workflows. When buildi
Product Hunt·3d ago
Building a Software Factory with Claude Code: From AI-Assisted Coding to Agentic Development
This article provides a comprehensive guide on building a software factory using Claude Code and other AI coding tools. It covers the evolut
freecodecamp.org·3d ago