War story: the hardest bug I ever debugged

And somewhere out there is a person reading this post and coming to the conclusion "How can Google be stupid enough to hire people stupid enough to have abs() return a negative value."

Love the story! There is so much complexity in the world around as that seemingly obviously wrong things happen through the most unlikely chains of dependency.

> And somewhere out there is a person reading this post and coming to the conclusion "How can Google be stupid enough to hire people stupid enough to have abs() return a negative value."

Weird things can happen anywhere but I was wondering why this issue wasn't caught by test cases before it escaped to production? I would think that a compiler team would have low-level tests for such common functions.