71–80 of 233 posts
The worst thing that strikes fear into me is seeing floating points used for real world currency. Dear god. So many things can go wrong. I always use unsigned integers counting number of cents. And if I gotta handle multiple currencies, then I'll use or make a wrapper class.
Earlier quoted context omitted.
> 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…
> (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.
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.
I get the feeling that the real problem here are the IEEE specs themselves. They include a huge bunch of restrictions that each individually aren't relevant to something like 99.9% of floating point code, and probably even in aggregate not a single one is relevant to a large majority of code segments out in the wild. That doesn't mean they're not important - but some of these features should have been locally opt-in,…
How does IEEE 754 prevent auto-vectorisation?
The worst thing that strikes fear into me is seeing floating points used for real world currency. Dear god. So many things can go wrong. I always use unsigned integers counting number of cents. And if I gotta handle multiple currencies, then I'll use or make a wrapper class.
How do you store negative numbers?
“Nothing brings fear to my heart more than a floating point number.” - Gerald Jay Sussman Is there any IEEE standards committee working on FP alternative for examples Unum and Posit [1],[2]. [1] Unum & Posit: https://posithub.org/about [2] The End of Error: https://www.oreilly.com/library/view/the-end-of/978148223986...
Is this sarcasm? If not, the proposed posit standard, IEEE P3109.
I helped design an API for "algebraic operations" in Rust: https://github.com/rust-lang/rust/issues/136469 >, which are coming along nicely. These operations are 1. Localized, not a function-wide or program-wide flag. 2. Completely safe, -ffast-math includes assumptions such that there are no NaNs, and violating that is undefined behavior . So what do these algebraic operations do? Well, one by itself doesn't do much…
The library has some merit, but the goal you've stated here is given to you with 5 compiler flags. The benefit of the library is choosing when these apply.
Earlier quoted context omitted.
How does IEEE 754 prevent auto-vectorisation?
If you write a loop `for x in array { sum += x }` Then your program is a specification that you want to add the elements in exactly that order, one by one. Vectorization would change the order.
The worst thing that strikes fear into me is seeing floating points used for real world currency. Dear god. So many things can go wrong. I always use unsigned integers counting number of cents. And if I gotta handle multiple currencies, then I'll use or make a wrapper class.
I always have a wrapper class to put the logic of converting to whole currency units when and if needed, as well as when requirements change and now you need 4 digits past the decimal instead of 2, etc.
The worst thing that strikes fear into me is seeing floating points used for real world currency. Dear god. So many things can go wrong. I always use unsigned integers counting number of cents. And if I gotta handle multiple currencies, then I'll use or make a wrapper class.
Should I be running my accounting system on units of 10 billionths of a dollar?