[ajross]

> I get the feeling that the real problem here are the IEEE specs themselves.

Well, all standards are bad when you really get into them, sure.

But no, the problem here is that floating point code is often sensitive to precision errors. Relying on rigorous adherence to a specification doesn't fix precision errors, but it does guarantee that software behavior in the face of them is deterministic. Which 90%+ of the time is enough to let you ignore the problem as a "tuning" thing.

But no, precision errors are bugs. And the proper treatment for bugs is to fix the bugs and not ignore them via tricks with determinism. But that's hard, as it often involves design decisions and complicated math (consider gimbal lock: "fixing" that requires understanding quaternions or some other orthogonal orientation space, and that's hard!).

So we just deal with it. But IMHO --ffast-math is more good than bad, and projects should absolutely enable it, because the "problems" it discovers are bugs you want to fix anyway.

[chuckadams]

> (consider gimbal lock: "fixing" that requires understanding quaternions or some other orthogonal orientation space, and that's hard!)

Or just avoiding gimbal lock by other means. We went to the moon using Euler angles, but I don't suppose there's much of a choice when you're using real mechanical gimbals.

[ajross]

That is the "tuning" solution. And mostly it works by limiting scope of execution ("just don't do that") and if that doesn't work by having some kind of recovery method ("push this button to reset", probably along with "use this backup to recalibrate"). And it... works. But the bug is still a bug. In software we prefer more robust techniques.

FWIW, my memory is that this was exactly what happened with Apollo 13. It lost its gyro calibration after the accident (it did the thing that was the "just don't do that") and they had to do a bunch of iterative contortions to recover it from things like the sun position (because they couldn't see stars out the iced-over windows).

NASA would have strongly preferred IEEE doubles and quaternions, in hindsight.