The pitch sounded simple: take a well-known open-source library, port it to a new language, prove it behaves identically. Port Mortem 2026. 72 hours. I worked alone.
At kickoff, the organizers released a curated pool of 100 eligible open-source repositories for participants to choose from. Most people went for something manageable. I scrolled the list until I found the one that scared me the most.
This is the story of what I built, what broke me, how I proved correctness, and the bugs I didn't expect to find.
What I Picked From the List — And Why It Was Probably Stupid
decimal.js is a JavaScript library for arbitrary-precision decimal arithmetic. Not a toy. Not a utility. A full numeric engine:
