I’ve done a few different reverse-engineering projects with LLMs, and figured it’s time to push the clankers to their limits. A 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. SPECIF~1.RAR RAR was originally an LZSS compressor for DOS, which peaked in popularity as the warez scene’s format of choice. Fighting with WinZip for feature parity and supremacy, WinRAR boasted multi-volume support, recovery records and even an internal VM, but its USP was always superior compression. It’s a middle-aged format that never stopped growing up, it’s as big as a house.…