Programming

At midnight UTC on January 1, 2017, deep inside Cloudflare’s custom RRDNS software, a number went negative when it should have always been at least zero. This single value caused DNS resolutions to fail across Cloudflare’s global network. The culprit? A leap second—one extra tick of the clock that most people never noticed. The bug revealed a fundamental truth that every programmer eventually learns the hard way: time is not what you think it is. It doesn’t flow uniformly forward. It jumps, skips, and occasionally rewinds. And if your code assumes otherwise, it will break in ways that are nearly impossible to predict. ...

Type 0.1 + 0.2 into any browser console, Python REPL, or JavaScript runtime. The answer comes back as 0.30000000000000004. This isn’t a bug. It’s not an error in your programming language. It’s the inevitable consequence of a fundamental tension: humans count in base 10, but computers count in base 2. The IEEE 754 floating-point standard, adopted in 1985, unified how computers represent decimal numbers. Before this standard, different machines handled floating-point arithmetic differently—code that worked on one system could produce completely different results on another. William Kahan, the primary architect of IEEE 754, designed a system that traded perfect precision for predictability. Every programmer would get the same answer, even if that answer wasn’t mathematically exact. ...